Integrating Plant Physiology and Microbiome Engineering for Climate‐Resilient Crops: Bridging Knowledge Gaps in Multi‐Stress Tolerance

ABSTRACT

Climate change is intensifying the frequency and co‐occurrence of abiotic and biotic stresses, posing significant challenges to global crop productivity and stability. Conventional approaches based on single‐stress responses are increasingly insufficient for addressing complex field environments where plants experience multiple simultaneous stresses. This review synthesizes current knowledge on plant physiological responses, microbiome interactions, and emerging technological interventions to develop an integrative framework for climate‐resilient agriculture. It highlights how stress perception, hormonal regulation, metabolic adjustments, and epigenetic mechanisms collectively shape plant adaptation under multi‐stress conditions. The review further examines the role of plant‐associated microbiomes in enhancing nutrient acquisition, regulating stress signaling, and improving resilience through mechanisms such as phytohormone modulation, antioxidant activity, and induced systemic resistance. Advances in microbiome engineering, including synthetic microbial communities and computational prediction frameworks, are discussed as promising strategies for improving stress tolerance. In addition, emerging tools such as nanotechnology‐assisted delivery systems and biosensing platforms are considered for precision management of plant–microbe systems. By identifying critical knowledge gaps in multi‐stress physiology, microbiome assembly, and field‐level predictability, this review proposes an interdisciplinary approach that integrates plant physiology, microbial ecology, and technological innovations to support sustainable crop production under changing climatic conditions.

1. Introduction

Global agriculture is increasingly vulnerable as climate change intensifies environmental stresses affecting crop production systems. Rising atmospheric CO₂ concentrations, increasing temperatures, irregular rainfall, and more frequent extreme events such as droughts, floods, heat waves, and salinity intrusions are collectively reducing crop productivity and stability worldwide. Recent assessments by the IPCC (2023) and studies by Wheeler and von Braun (2013) highlight growing risks to global food systems, with projections indicating yield losses of 10%–25% for major staples such as wheat, rice, and maize by mid‐century if adaptive measures are not strengthened (Lobell et al. 2011). These impacts are particularly severe in developing regions where agriculture remains largely rain‐fed and closely linked to livelihoods. Conventional breeding and agronomic approaches, developed under relatively stable climatic conditions, are increasingly inadequate for addressing complex and interacting stress environments. This necessitates a shift toward integrative frameworks that prioritize resilience and sustainability alongside productivity.

Traditionally, plant stress research has focused on individual stress factors such as drought, salinity, or heat. However, crops in real‐world environments are exposed to multiple stresses simultaneously, producing responses that are often non‐additive and unpredictable. Studies by Mittler (2006), Ramegowda and Senthil‐Kumar (2015), and Suzuki et al. (2014) demonstrate that combined stresses trigger distinct physiological and molecular adjustments involving carbon allocation, hormonal crosstalk, redox regulation, and defense prioritization. These complex responses reveal a significant knowledge gap in understanding how plants coordinate adaptive mechanisms under concurrent stresses and how such mechanisms can be enhanced for agricultural resilience.

Parallel advances in plant biology have redefined plants as holobionts—integrated systems consisting of the host plant and its associated microbiome, including bacteria, fungi, archaea, and viruses inhabiting different plant compartments. Research by Vandenkoornhuyse et al. (2015), Berendsen et al. (2012), and Compant et al. (2019) highlights the critical role of microbial communities in nutrient acquisition, stress tolerance, and plant health. Beneficial microbes influence hormonal balance, enhance water and nutrient uptake, and prime defense pathways, suggesting strong potential for microbiome‐based interventions. Integrating plant physiological traits with microbiome engineering, therefore, represents a promising pathway toward climate‐resilient cropping systems.

This review synthesizes current knowledge linking plant physiology, microbiome science, and multi‐stress tolerance. It examines interactions between physiological processes and microbial functions under combined stress scenarios and explores emerging strategies such as microbial inoculants, synthetic communities, and microbiome‐informed breeding. By identifying knowledge gaps and future research priorities, the review proposes an integrative framework for harnessing plant–microbe interactions to support sustainable and climate‐resilient agriculture.

2. Plant Responses to Abiotic Stress

Plant adaptation to abiotic stress depends on a coordinated network of physiological, biochemical, and molecular processes that integrate multiple environmental signals into appropriate adaptive responses (Zandalinas et al. 2020; Li et al. 2024). As sessile organisms, plants have evolved sophisticated stress‐sensing and signaling networks involving hormonal regulation, calcium signaling, reactive oxygen species (ROS), transcriptional reprogramming, and metabolic adjustments that enable adaptation and survival under fluctuating environmental conditions (Hasanuzzaman et al. 2020; Li et al. 2024). Significant progress has been made in understanding plant stress physiology at molecular, cellular, and whole‐plant levels. However, much of this knowledge originates from single‐stress experiments conducted under controlled environments, which do not fully represent the dynamic and multi‐stress conditions typical of agricultural systems. Increasing evidence indicates that plant stress responses are governed not only by genetic programs but also by hormonal cross‐talk, metabolic trade‐offs, epigenetic regulation, and interactions with associated microbiomes, which collectively influence plant acclimation, resilience, and stress memory under changing environmental conditions (Verma et al. 2016; Trivedi et al. 2022; Lämke and Bäurle 2017). Despite significant advances in plant stress biology, major knowledge gaps remain in understanding how plants integrate multiple stress signals, distinguish stress‐induced responses from developmental regulation, and optimize resource allocation between growth and defense under complex environmental conditions (Mittler 2006; Suzuki et al. 2014; Ramegowda and Senthil‐Kumar 2015). This section summarizes the current understanding of abiotic stress responses across molecular signaling, hormonal regulation, metabolic adjustments, and epigenetic mechanisms, while highlighting unresolved challenges limiting the development of climate‐resilient crops. The integrated molecular pathways involved in stress perception, signaling crosstalk, metabolic reprogramming, and adaptive responses are summarized in Figure 1, whereas major physiological and biochemical responses are presented in Table 1.

FIGURE 1.

Integrated molecular pathways of plant abiotic stress perception, hormonal crosstalk, and metabolic acclimation. Abiotic stresses (drought, salinity, heat, cold, heavy metals) are perceived at the plasma membrane by receptor‐like kinases (RLKs) and Ca²⁺ channels, triggering cytosolic Ca²⁺ influx, reactive oxygen species (ROS) burst, and MAPK signaling cascades. These signals converge on a hormonal regulation hub, abscisic acid (ABA), ethylene (ET), jasmonic acid (JA), salicylic acid (SA), and auxin/cytokinin, whose crosstalk (bidirectional arrows) activates transcription factors (DREB/CBF, ERFs, WRKY, bZIP) via cis‐elements (ABRE, DRE/CRT). Downstream metabolic adjustments include osmolyte accumulation (proline, glycine betaine, trehalose), antioxidant enzyme activation (SOD, CAT, APX, GR), and stress‐protective protein expression (HSPs, LEA proteins), collectively enhancing root architecture, stomatal regulation, and whole‐plant stress tolerance.

TABLE 1.

Plant physiological responses to abiotic stress and knowledge gaps.

Physiological domain	Mechanistic and adaptive processes	Unresolved scientific challenges	References
Molecular signaling	MAPK/CDPK and SnRK2 kinase cascades. ROS/Ca2+ secondary messenger signatures. Activation of DREB/CBF, NAC, and WRKY transcription factors.	Decoding overlapping signatures during simultaneous multi‐stress events. Distinguishing stress‐induced vs. developmental hypoxia.	Rehman and Mahmood (2015), Agarwal and Ray (2020), Feng and Xia (2025)
Hormonal crosstalk	ABA‐mediated stomatal closure and osmoprotection. SA/JA/ethylene coordination for defense. Auxin/brassinosteroid‐driven growth maintenance.	Mapping multidimensional hormone integration under concurrent, heterogeneous field stresses.	Rhaman et al. (2025), Ullah and Junjun (2025), Yetgin et al. (2025)
Metabolic adjustments	Biosynthesis of compatible solutes (e.g., proline, trehalose). Enzymatic and non‐enzymatic ROS detoxification. Stress‐induced carbon–nitrogen reallocation.	Optimizing growth vs. defense resource trade‐offs under prolonged or recurrent multifactorial stress.	Cui et al. (2024), Climent et al. (2024), Zhang et al. (2025)
Epigenetic memory	DNA methylation and histone modifications. Chromatin remodeling and sRNA‐directed post‐transcriptional regulation.	Elucidating triggers of memory formation, temporal persistence, and transgenerational inheritance mechanisms.	Carbó et al. (2019), Fitz‐James and Cavalli (2022), Del Vecchio (2025)

Recent studies indicate that plant responses to abiotic stress involve highly coordinated interactions among molecular signaling networks, transcriptional regulation, phytohormonal crosstalk, and metabolic reprogramming. Under drought, salinity, heat, and oxidative stress conditions, plants activate complex signaling cascades involving reactive oxygen species (ROS), calcium signaling, mitogen‐activated protein kinases (MAPKs), and stress‐responsive transcription factors such as Dehydration‐Responsive Element‐Binding (DREB) proteins, NAM, ATAF1/2, and CUC2 (NAC) transcription factors, WRKY‐domain‐containing (WRKY) transcription factors, and Basic Leucine Zipper (bZIP) families (Zandalinas et al. 2020; Li et al. 2024). These integrated responses regulate osmotic adjustments, antioxidant defense, stomatal conductance, ion homeostasis, and cellular protection, thereby enhancing plant resilience under fluctuating environmental conditions.

2.1. Metabolic and Physiological Adjustments

Plant adaptation to abiotic stress is first manifested through physiological and metabolic adjustments that maintain cellular homeostasis, water balance, energy metabolism, and photosynthetic functions. These responses represent the integrated outcome of stress perception and signaling processes and provide the functional basis for survival under adverse environmental conditions (Zandalinas et al. 2020). Understanding these physiological adaptations is therefore essential before examining the underlying molecular and regulatory mechanisms that govern stress responses.

Abiotic stress disrupts cellular homeostasis, energy balance, and metabolic fluxes, necessitating extensive physiological and metabolic reprogramming (Hasanuzzaman et al. 2020; Zandalinas et al. 2020). One of the earliest responses is the accumulation of compatible solutes such as proline, glycine betaine, trehalose, and soluble sugars, which stabilize proteins and membranes, maintain osmotic balance, and contribute to ROS scavenging (Ashraf and Foolad 2007). These metabolites also function as signaling molecules influencing stress‐responsive gene expression. For example, in rice ( Oryza sativa ) and wheat ( Triticum aestivum ) exposed to drought and salinity stress, proline accumulation has been associated with ABA‐mediated signaling, ROS detoxification, and activation of stress‐responsive genes involved in osmotic adjustments and antioxidant defense (Hayat et al. 2012; Kaur and Asthir 2015). In Arabidopsis thaliana , proline functions as a regulatory metabolite influencing mitochondrial redox balance and stress‐induced gene expression during osmotic and oxidative stress (Szabados and Savouré 2010). Similarly, glycine betaine acts as both an osmoprotectant and signaling metabolite in maize ( Zea mays ) and tomato ( Solanum lycopersicum ) under salinity and heat stress by stabilizing photosynthetic machinery, modulating antioxidant enzyme activity, and enhancing stress signaling pathways linked to cellular protection (Ashraf and Foolad 2007; Annunziata et al. 2017). Other metabolites such as trehalose and soluble sugars have also been reported to participate in stress signaling by regulating carbon metabolism, ROS homeostasis, and hormone crosstalk under drought and temperature stress conditions (Paul et al. 2008; Sami et al. 2016).

Stress conditions frequently lead to oxidative stress due to excessive ROS production in chloroplasts, mitochondria, and peroxisomes (Majumdar et al. 2023). Plants counteract oxidative damage through antioxidant defense systems comprising enzymatic components such as superoxide dismutase, catalase, and ascorbate peroxidase, along with non‐enzymatic antioxidants including ascorbate, glutathione, carotenoids, and phenolic compounds (Gill and Tuteja 2010; Gupta et al. 2022). Maintaining a balance between ROS signaling and detoxification is essential for effective stress tolerance. Abiotic stress also induces extensive metabolic reconfiguration to maintain cellular homeostasis and energy balance. Accumulation of osmoprotectants such as proline, glycine betaine, soluble sugars, and polyamines contributes to osmotic adjustments and membrane stabilization. Simultaneously, activation of enzymatic and non‐enzymatic antioxidant systems helps minimize oxidative damage caused by excessive ROS generation (Sun et al. 2025). Recent studies further highlight the role of metabolic flexibility and carbon‐nitrogen balance in sustaining plant growth and stress acclimation under climate‐induced environmental variability (Cui et al. 2024). It also reduces photosynthetic carbon assimilation through stomatal closure and metabolic limitations, resulting in altered carbon–nitrogen partitioning and reallocation of resources toward protective metabolites and stress‐related proteins (Flexas et al. 2016).

Beyond their damaging effects, reactive oxygen species (ROS) also function as essential signaling molecules that regulate stress perception, acclimation, and defense gene activation. Therefore, strategic manipulation of ROS signaling and the antioxidant machinery represents a promising approach for improving plant resilience under multifactorial stress conditions. Controlled enhancement of enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) through transgenic approaches, genome editing, or stress‐inducible promoters has been shown to maintain cellular redox balance and improve stress tolerance without severely compromising growth (Mittler 2017). Recent studies further demonstrate that modulation of ROS‐responsive transcription factors including WRKY, NAC, DREB, and bZIP families can fine‐tune stress signaling networks and improve tolerance to drought, salinity, and heat stress (Zandalinas et al. 2020). In addition, the exogenous application of signaling molecules, osmoprotectants, and microbial biostimulants can induce antioxidant priming, thereby enhancing ROS scavenging capacity and membrane stability under stress. Plant growth‐promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) are particularly important because they regulate antioxidant enzyme activity, improve osmotic adjustments, and modulate ROS–phytohormone crosstalk, collectively contributing to sustained plant growth under adverse environments (Vurukonda et al. 2016; Begum et al. 2019). From an applied perspective, future climate‐resilient crop improvement strategies should integrate redox engineering, microbiome‐assisted stress management, and precision breeding approaches to optimize ROS homeostasis while minimizing oxidative injury.

While these adjustments enhance survival, they often reduce growth and yield. A key unresolved challenge is to understand how plants optimize metabolic resource allocation between growth and defense under prolonged or recurring stress conditions, particularly in multi‐stress environments.

2.2. Hormonal Regulation in Stress Adaptation

Plant hormones function as central integrators of stress signals, coordinating physiological responses while maintaining growth and development. Rather than acting independently, phytohormones operate through interconnected networks that enable context‐dependent adaptation. Among these, abscisic acid (ABA) is a primary regulator of responses to drought, salinity, and osmotic stress. Stress‐induced ABA accumulation promotes stomatal closure, osmoprotective gene expression, and root system plasticity through the PYR/PYL–PP2C–SnRK2 signaling pathway (Cutler et al. 2010). ABA signaling further activates several stress‐responsive osmoprotective genes that contribute to cellular dehydration tolerance and osmotic adjustments under drought and salinity stress. Important ABA‐inducible genes include Responsive to Desiccation 29A (RD29A), RAB18, Late Embryogenesis Abundant (LEA) proteins, and dehydrin‐encoding genes, which help stabilize cellular membranes and proteins during water deficit conditions (Yamaguchi‐Shinozaki and Shinozaki 2006; Cutler et al. 2010). ABA also regulates genes involved in osmolyte biosynthesis, particularly Δ1‐pyrroline‐5‐carboxylate synthetase (P5CS), a key enzyme in proline accumulation that supports osmotic balance and reactive oxygen species scavenging under stress (Szabados and Savouré 2010). In addition, ABA‐responsive transcription factors such as AREB/ABF and DREB coordinate downstream stress‐responsive gene networks, thereby enhancing plant adaptation to complex environmental stresses (Fujita et al. 2013; Ali et al. 2020).

However, sustained ABA signaling often suppresses growth and photosynthesis, emphasizing the need for precise spatial and temporal regulation. Hormones traditionally associated with biotic stress, including salicylic acid (SA), jasmonic acid (JA), and ethylene, also contribute to abiotic stress tolerance by modulating antioxidant defense, thermotolerance, senescence, and root architecture (Verma et al. 2016). SA, JA, and ethylene are increasingly recognized as critical regulators of abiotic stress adaptation through complex hormonal crosstalk and signaling coordination. In wheat and rice, SA has been reported to enhance drought and salinity tolerance by improving antioxidant enzyme activities, maintaining membrane stability, and regulating osmolyte accumulation, thereby reducing oxidative damage under stress conditions (Khan et al. 2015; Nazar et al. 2015). Jasmonic acid contributes significantly to abiotic stress resilience by modulating defense metabolism, antioxidant systems, and stress‐responsive gene expression. For example, exogenous JA application improved heat and salinity tolerance in tomato and soybean through enhanced photosynthetic stability and reactive oxygen species detoxification (Wani et al. 2016; Wasternack and Song 2017). Ethylene also plays a dual regulatory role in abiotic stress responses depending on stress intensity and developmental stage. In Arabidopsis and rice, ethylene signaling has been associated with improved adaptation to drought and flooding stress through regulation of stomatal behavior, senescence, and stress‐responsive transcription factors (Van de Poel et al. 2015; Nazir et al. 2024). These findings collectively demonstrate that hormonal interactions are central to plant acclimation under multiple environmental stresses. Growth‐promoting hormones such as auxins and brassinosteroids further influence stress adaptation by maintaining growth, regulating antioxidant activity, and supporting photosynthetic efficiency (Nolan et al. 2020).

The interactions of SA, JA and ethylene with ABA enable prioritization of stress responses but may also create antagonistic effects under combined stresses. Abiotic and biotic stresses converge on central signaling hubs involving reactive oxygen species (ROS), Ca²⁺ fluxes, MAPK cascades, and phytohormonal crosstalk among abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA), and ethylene (ET). Under drought and osmotic stress, ABA acts as a dominant regulator promoting stomatal closure, osmotic adjustment, and stress‐responsive gene expression; however, elevated ABA signaling frequently antagonizes SA‐mediated defense pathways that are essential for resistance against biotrophic pathogens. This antagonism is mediated through suppression of NPR1‐dependent signaling and modulation of WRKY transcription factors, leading to reduced expression of pathogenesis‐related (PR) genes (Cutler et al. 2010; Berens et al. 2017; Verma et al. 2016). In contrast, ABA often interacts synergistically with JA and ethylene signaling pathways, enhancing defense responses against necrotrophic pathogens and herbivorous insects through coordinated activation of stress‐responsive transcription factors and defense metabolites (Pieterse et al. 2012; Verma et al. 2016). Moreover, JA–ET signaling can counterbalance ABA‐mediated growth restriction and stomatal regulation under certain combined stress environments, highlighting the complex trade‐offs between drought adaptation, growth maintenance, and pathogen defense. Such hormonal crosstalk demonstrates that plant responses to simultaneous stresses are highly context dependent and cannot be explained through single‐hormone pathways alone.

Figure 1 further highlights the extensive hormonal crosstalk among ABA, jasmonic acid, salicylic acid, ethylene, and auxin pathways that collectively regulate adaptive responses under combined stress conditions. Emerging evidence suggests that stress adaptation is largely governed by phytohormonal crosstalk involving abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA), ethylene, auxins, cytokinins, and brassinosteroids. ABA acts as a central regulator of stomatal closure, osmotic balance, and stress‐responsive gene expression, whereas interactions among SA, JA, and ethylene mediate stress signaling integration between abiotic and biotic stress pathways. Such hormonal interactions enable plants to fine‐tune growth‐defense trade‐offs under combined stress environments (Gupta et al. 2020; Vishwakarma et al. 2017). Despite extensive characterization of individual hormonal pathways, a major knowledge gap persists in understanding how plants integrate multiple hormonal signals under concurrent stresses. Current models derived from single‐stress conditions remain insufficient for predicting plant behavior in complex field environments where multiple stresses often occur simultaneously.

Recent evidence further indicates that beneficial rhizosphere microorganisms play an important role in improving plant performance under combined abiotic stresses, although such studies remain comparatively limited and are often conducted under controlled conditions. Plant growth–promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi (AMF), and stress‐adapted microbial consortia can alleviate the detrimental effects of simultaneous drought, salinity, and heat stresses through multiple complementary mechanisms. These include modulation of phytohormonal balance, enhancement of antioxidant defense systems, osmolyte accumulation, improved nutrient uptake, maintenance of root hydraulic conductivity, and regulation of stress‐responsive genes (Khan et al. 2019). Several PGPR strains possessing ACC deaminase activity have been reported to reduce stress‐induced ethylene accumulation, thereby sustaining root growth and photosynthetic efficiency under combined drought–salinity or heat–drought conditions. Similarly, AMF associations contribute to improved water‐use efficiency, ion homeostasis, and membrane stability during multiple stress exposures by enhancing phosphorus acquisition and maintaining cellular redox balance (Begum et al. 2019). Emerging studies also suggest that microbial consortia may provide greater resilience than single inoculants because of functional complementarity among microbial taxa, enabling plants to better withstand fluctuating environmental conditions (Santoyo et al. 2021). Although many of these investigations have been performed in greenhouse or controlled systems, they collectively emphasize the critical role of the rhizosphere microbiome in shaping plant adaptation under complex multi‐stress environments and highlight the need for field‐scale validation under climate‐resilient agricultural systems.

2.3. Molecular Mechanisms of Abiotic Stress Perception and Signaling

Abiotic stress responses begin with rapid perception of environmental changes followed by signal transduction processes that reprogram cellular activity. Stress perception occurs through membrane‐bound receptors, organellar signals, and alterations in cellular homeostasis such as osmotic pressure, redox balance, calcium fluxes, and energy status (Zhu 2016). Plants detect stress through receptor‐like kinases, mechanosensitive ion channels, and intracellular sensors that respond to ionic, osmotic, oxidative, or temperature fluctuations. These early signaling events are essential because they allow plants to rapidly initiate protective responses before irreversible cellular injury occurs, thereby maintaining membrane integrity, photosynthetic efficiency, osmotic balance, and metabolic stability under stress conditions (Dodd et al. 2010; Zhu 2016).

Stress perception activates interconnected signaling cascades involving mitogen‐activated protein kinases (MAPKs), calcium‐dependent protein kinases (CDPKs), SNF1‐related protein kinase 2 (SnRK2), CBL‐interacting protein kinases (CIPKs), and SNF1‐related kinase 1 (SnRK1), which together orchestrate early adaptive responses. MAPK cascades rapidly transduce extracellular stress signals into transcriptional responses by phosphorylating downstream transcription factors such as WRKY33, WRKY25, ERF6, and members of the DREB family, which regulate genes associated with osmotic adjustment, antioxidant defense, and abiotic stress acclimation. MAPK signaling also targets stress‐responsive proteins including heat shock proteins (HSP70 and HSP90), antioxidant enzymes such as ascorbate peroxidase (APX) and superoxide dismutase (SOD), as well as regulators of programmed cell death and cellular protection (Sinha et al. 2011; Jalmi and Sinha 2015). Through these coordinated phosphorylation events, MAPKs integrate reactive oxygen species, calcium, and hormonal signals to enhance stress adaptation under drought, salinity, heat, and oxidative stress conditions (Meng and Zhang 2013; Danquah et al. 2014). CDPKs decode calcium signatures generated during stress and regulate ion channels, ROS‐scavenging enzymes, and ABA‐responsive genes that contribute to stomatal regulation and cellular protection (Schulz et al. 2013). The ABA‐dependent SnRK2 pathway activates stress‐responsive transcription factors such as AREB/ABF proteins and regulates genes associated with osmoprotection, dehydration tolerance, and antioxidant defense (Cutler et al. 2010). Similarly, CIPK signaling modules interact with calcineurin B‐like (CBL) proteins to regulate ion transporters and maintain ionic homeostasis during salinity and nutrient stress (Quan et al. 2007).

Under salt stress, the well‐characterized Salt Overly Sensitive (SOS) pathway involves the calcium sensor CBL4 (SOS3), which interacts with CIPK24 (SOS2) to activate the plasma membrane Na⁺/H⁺ antiporter SOS1, thereby promoting Na⁺ extrusion and maintaining cellular ion balance (Shi et al. 2002). The CBL4–CIPK24 complex has also been implicated in the regulation of vacuolar Na⁺/H⁺ exchangers (NHX), facilitating intracellular Na⁺ sequestration and enhancing salt tolerance (Ragel et al. 2015). In addition, potassium homeostasis is regulated through specific CBL–CIPK modules, including CBL1/CBL9–CIPK23 and CBL1/CBL4–CIPK6, which modulate the activity of AKT1 and other potassium transporters involved in K⁺ uptake, transport, and retention under stress conditions. These signaling networks enable plants to maintain optimal Na⁺/K⁺ balance, a critical determinant of abiotic stress tolerance (Luan 2009; Quan et al. 2007; Shi et al. 2002; Xu et al. 2006; Ragel et al. 2015). In parallel, SNF1‐related kinase 1 (SnRK1), represented by KIN10 and KIN11 in Arabidopsis, functions as a master cellular energy sensor that reprograms metabolism during stress by coordinating carbon utilization, starch degradation, autophagy, and stress‐responsive gene expression under energy‐limiting conditions. During hypoxia, flooding, and anaerobic germination, SnRK1 promotes carbohydrate remobilization through activation of α‐amylase genes and associated starch‐degrading enzymes, thereby maintaining cellular ATP supply and supporting seedling establishment under oxygen‐deficient conditions. SnRK1 also activates autophagy pathways through regulation of autophagy‐related genes including ATG1, ATG6, ATG8, and ATG18, facilitating degradation and recycling of damaged proteins and organelles during prolonged stress. Furthermore, SnRK1 regulates several stress‐responsive transcription factors and protective proteins such as bZIP63, DREB2A, WRKY, and NAC family members, as well as heat shock proteins (HSPs), thereby integrating energy status with hormonal signaling, antioxidant defense, and adaptive stress responses. Through these functions, SnRK1 serves as a critical hub linking metabolic homeostasis, nutrient remobilization, and stress acclimation under drought, salinity, flooding, and other adverse environmental conditions (Baena‐González and Sheen 2008; Jamsheer et al. 2021; Soto‐Burgos and Bassham 2017; Cho et al. 2012).

Secondary messengers further amplify these responses, where calcium signatures encode stress‐specific information decoded by calcium sensors, while reactive oxygen species (ROS) act both as damaging molecules and essential signaling intermediates regulating gene expression and hormonal pathways (Mittler 2017). Key calcium‐binding proteins involved in abiotic stress signaling include calmodulins (CaMs), calcineurin B‐like proteins (CBLs), CBL‐interacting protein kinases (CIPKs), and calcium‐dependent protein kinases (CDPKs/CPKs). These calcium sensors decode transient cytosolic Ca²⁺ signatures generated in response to drought, salinity, heat, flooding, and oxidative stress, thereby activating downstream phosphorylation cascades, transcriptional regulators, and ion transport systems. For example, the CBL–CIPK network regulates ionic homeostasis during salinity stress through modulation of Na⁺/H⁺ antiporters, whereas CDPKs integrate calcium and reactive oxygen species signaling to regulate antioxidant defense and stress‐responsive gene expression. Calmodulin‐mediated signaling further coordinates hormonal cross‐talk involving abscisic acid (ABA), jasmonic acid, and ethylene pathways. The temporal and spatial specificity of calcium oscillations enables plants to distinguish among different stress combinations and rapidly prioritize adaptive responses, making calcium signaling an essential early integrative mechanism for acclimation under multiple abiotic stress conditions (Dodd et al. 2010; Kudla et al. 2018; Thor et al. 2020).

However, the mechanisms by which calcium‐mediated signals are integrated with ROS, hormonal, and kinase‐dependent pathways during simultaneous stress exposure remain poorly understood. Addressing this knowledge gap is critical for understanding plant adaptation under complex field environments. Downstream signaling networks converge on transcription factor families such as DREB/CBF, NAC, WRKY, MYB, and bZIP, which regulate genes involved in osmotic adjustment, antioxidant defense, and cellular protection. The interconnected signaling pathways involved in stress sensing, calcium influx, ROS generation, MAPK activation, and downstream transcriptional regulation are collectively illustrated in Figure 1. Reactive oxygen species (ROS) act as a double‐edged component of plant stress responses, exerting both signaling and cytotoxic effects depending on their concentration, duration, and cellular localization. Under moderate or transient stress, ROS such as hydrogen peroxide (H₂O₂), superoxide radicals (O₂•−), and singlet oxygen function as important secondary messengers that regulate stress perception, stomatal movement, hormonal crosstalk, gene expression, and activation of antioxidant defenses. Controlled ROS accumulation can initiate acclimation responses by activating MAPK cascades, calcium signaling pathways, transcription factors, and stress‐responsive genes involved in osmoprotection and cellular repair (Mittler 2017; Gill and Tuteja 2010). However, excessive ROS production under prolonged or severe abiotic stress disrupts redox homeostasis, causing lipid peroxidation, protein oxidation, membrane injury, DNA damage, and programmed cell death. Therefore, maintaining ROS balance is critical for plant survival under combined stresses. Plants regulate ROS homeostasis through coordinated enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase, together with non‐enzymatic antioxidants including ascorbate, glutathione, carotenoids, and flavonoids. Emerging studies further demonstrate that ROS signaling can be strategically manipulated to improve climate resilience through microbiome‐assisted antioxidant enhancement, exogenous priming agents, nanotechnology‐based protectants, and genetic engineering of redox‐sensitive signaling networks. Beneficial microbes including PGPR and endophytes can modulate ROS detoxification pathways and maintain cellular redox balance under drought, salinity, and heat stress, thereby improving stress tolerance and physiological performance under multi‐stress environments (Vurukonda et al. 2016).

Although cross‐regulation among transcription factors provides flexibility in stress responses, redundancy and pleiotropic effects complicate their application in crop improvement. In addition, plants experience hypoxia both under environmental stresses such as flooding or waterlogging and during normal developmental processes including seed germination and meristematic growth. Since several oxygen‐sensing mechanisms and hypoxia‐responsive genes are shared between these conditions, distinguishing stress‐specific responses from developmentally regulated hypoxia remains challenging. This overlap complicates the identification of regulatory pathways that can be selectively targeted for engineering flood‐tolerant crops without adversely affecting normal plant growth and development (van Dongen and Licausi 2015; Bailey‐Serres and Voesenek 2008).

Recent advances in omics technologies have significantly improved the understanding of plant stress adaptation mechanisms. Transcriptomic, proteomic, metabolomic, and epigenomic studies reveal that abiotic stress tolerance is regulated through dynamic gene expression, chromatin remodeling, alternative splicing, and stress memory mechanisms. Epigenetic modifications, including DNA methylation and histone modifications, are increasingly recognized as important regulators of transgenerational stress adaptation and stress priming in plants (Boyko et al. 2010; Sani et al. 2013; Hasanuzzaman et al. 2020).

2.4. Epigenetic Regulation and Stress Memory

Plants exhibit remarkable phenotypic plasticity that enables acclimation to recurrent environmental stresses through mechanisms collectively referred to as stress memory. Stress memory allows plants to respond more rapidly and effectively to subsequent stress exposure by maintaining physiological, transcriptional, and metabolic preparedness (Bruce et al. 2007; Crisp et al. 2016). Epigenetic regulation provides a reversible and heritable layer of gene expression control without altering the underlying DNA sequence, thereby facilitating adaptive responses to repeated stress events through DNA methylation, histone modifications, chromatin remodeling, and stress‐induced transcriptional memory (Kinoshita and Seki 2014; Lämke and Bäurle 2017; Friedrich et al. 2019). DNA methylation plays a central role in regulating stress‐responsive genes, with abiotic stresses inducing dynamic changes in methylation patterns that influence transcriptional activity (Kinoshita and Seki 2014). Some methylation changes persist after stress removal, suggesting a role in stress priming. Histone modifications, including acetylation and methylation, regulate chromatin accessibility and facilitate rapid activation of stress‐responsive genes during repeated exposure (Lämke and Bäurle 2017). Several stress‐responsive genes have been reported to be regulated through epigenetic modifications during abiotic stress adaptation. For instance, drought‐responsive genes such as DREB2A (Dehydration Responsive Element Binding Protein 2A) and RD29A are activated through histone acetylation and reduced DNA methylation, thereby enhancing transcriptional responsiveness under water‐deficit conditions (Kim et al. 2015; Lämke and Bäurle 2017). Similarly, the salinity‐responsive transporter gene HKT1 is regulated through RNA‐directed DNA methylation pathways that influence sodium homeostasis and salt tolerance (Baek et al. 2011). Genes involved in abscisic acid biosynthesis and osmotic adjustment, including NCED3 and P5CS1, also exhibit chromatin remodeling and histone modification‐mediated regulation during drought and heat stress acclimation (Kinoshita and Seki 2014). In addition, heat stress memory has been associated with sustained histone H3K4 methylation at loci such as HSP70 and APX2, allowing plants to maintain a primed transcriptional state upon recurrent stress exposure (Liu et al. 2022). These findings demonstrate that epigenetic regulation of key stress‐responsive genes plays a crucial role in plant adaptation, stress memory, and climate resilience under fluctuating environmental conditions.

Chromatin remodeling further enhances transcriptional flexibility by altering nucleosome positioning. Small RNAs, particularly microRNAs and small interfering RNAs, contribute to stress memory through post‐transcriptional regulation and maintenance of genome stability (Sunkar et al. 2012). Evidence also indicates that certain stress‐induced epigenetic changes may be transmitted across generations, providing enhanced tolerance in progeny (Herman and Sultan 2011). The integration of plant signaling pathways with microbiome‐mediated stress modulation and defense priming is conceptually represented in Figure 1. Plant's cellular stress signals that are genetically inherited as memories can trigger signaling cascades; however, such mechanisms are not fully understood yet. Addressing these gaps is essential for harnessing epigenetic regulation in breeding and engineering climate‐resilient crops.

3. Plant–Microbiome Interactions in Stress Alleviation

Plants function as holobionts, hosting diverse microbial communities in roots, internal tissues, and aerial organs. These microbiomes influence plant adaptation to drought, salinity, heat, and nutrient limitations by modulating stress perception, hormone signaling, and nutrient acquisition (Sivakumar et al. 2020). The effects of microbial associations depend on community composition, spatial organization, and functional traits (Willing et al. 2024; Ning et al. 2024; Bernardin et al. 2025). Understanding these interactions is increasingly important for developing climate‐resilient crops under multifactorial stress conditions where single‐stress models are inadequate (Liang, Yu, Ju, et al. 2025; Gelaye et al. 2026; Figure 2). The understanding of interactions between plants and beneficial microbes remains poorly resolved, as environmental variation of stressors and mechanisms of tolerance are also partially unresolved (Tariq et al. 2025; Wankhade et al. 2025).

FIGURE 2.

Plant–microbiome interactions across the rhizosphere, endosphere, and phyllosphere: Root exudation‐driven microbiome recruitment and stress alleviation. The three compartments of the plant microbiome are depicted in cross‐section. Phyllosphere: Epiphytic bacteria provide UV protection, pathogen suppression, and volatile organic compound (VOC) exchange, triggering induced systemic resistance (ISR). This figure shows a perspective view of a model plant‐microbial association on the phyllosphere (in the inset). Endosphere: Endophytic bacteria perform N₂ fixation, phytohormone production (IAA, cytokinins), ACC deaminase‐mediated ethylene reduction, siderophore‐based Fe³⁺ chelation, and phosphate solubilization. Rhizosphere: Root‐secreted exudates, sugars, organic acids, flavonoids, strigolactones, and mucilage create concentration gradients that selectively recruit beneficial microorganisms: Flavonoids recruit Rhizobium spp., organic acids attract Pseudomonas spp., sugars recruit Bacillus spp., and strigolactones stimulate arbuscular mycorrhizal fungi (AMF). Recruited PGPR form biofilms on root surfaces, immobilize heavy metals (As, Cd, Pb) via EPS binding, and confer induced systemic tolerance (IST) and biocontrol functions.

3.1. Microbiome Assembly and Plant Recruitment Strategies for Stress Alleviation

The plant microbiome is spatially organized into the rhizosphere, endosphere, and phyllosphere, each shaped by distinct abiotic filters and host‐driven selection pressures (Zhao et al. 2026). These compartments function as an interconnected system, where metabolites, signals, and microbes move across interfaces, generating emergent properties especially under fluctuating stress. Spatial compartmentalisation is particularly important under multi‐stress scenarios because each niche contributes distinct functional roles in stress mitigation, including nutrient acquisition, osmotic adjustments, antioxidant regulation, and pathogen suppression (Compant et al. 2019; Trivedi et al. 2022). The differential microbial assembly and activity across these compartments enhance the ecological buffering capacity and allow plants to coordinate localized and systemic responses to simultaneous abiotic and biotic stresses, thereby improving the overall resilience of the plant holobiont (Berendsen et al. 2012; Vandenkoornhuyse et al. 2015).

The rhizosphere, structured by root exudates and mucilage (Nazari et al. 2023), is the most taxonomically diverse compartment. It hosts bacteria, fungi, archaea, and protists involved in nutrient cycling, hormone modulation, and detoxification. Under stress, communities shift toward stress‐tolerant taxa, including osmoprotectant‐producing bacteria and melanized fungi, buffering the microenvironment relative to bulk soil (Munir et al. 2022; Wang et al. 2023; Goszcz et al. 2025). The endosphere comprises microbes that successfully colonize internal tissues after overcoming host barriers (Adeleke and Babalola 2022). Within this buffered niche, endophytes influence vascular function, hydraulic conductance, and hormonal gradients, roles that intensify under stress (Pandey et al. 2023). The phyllosphere, exposed to UV radiation and thermal extremes, supports specialized microbial assemblages (Mir et al. 2022; Negi et al. 2026) that regulate cuticular traits, stomatal behavior, and ROS homeostasis, contributing to resilience under heat and high light.

Microbiome assembly draws from soil, air, and seed pools and reflects both deterministic (genotype, development, exudation, soil traits) and stochastic processes (drift, dispersal limitation, historical contingency; Robert et al. 2025; Martins et al. 2026; Liu et al. 2025). Stress reshapes filters and host signals, favoring stress‐adapted, biofilm‐forming taxa and reinforcing priority effects (Portas et al. 2024; Roganovic et al. 2025). Functional guilds are central to stress mitigation. PGPR enhance nutrient solubilization and phytohormone production (Vocciante et al. 2022; Bhat et al. 2023; Hasan et al. 2024), arbuscular mycorrhizal fungi extend nutrient and water access (Wang et al. 2022), and endophytes enhance plant stress tolerance through the accumulation of osmoprotectants and the activation of antioxidant defense systems (Pandey et al. 2023; Shaffique et al. 2022; Byregowda et al. 2022).

Beyond direct phytohormone synthesis, several PGPR and rhizosphere‐associated microorganisms improve plant resilience through nutrient solubilization and biochemical modulation of stress responses. Phosphate‐solubilizing bacteria such as Bacillus, Pseudomonas, and Rhizobium mobilize insoluble phosphorus through the secretion of organic acids and phosphatases, while potassium‐ and zinc‐solubilizing microorganisms enhance micronutrient availability and nutrient uptake efficiency under nutrient‐deficient or stress‐prone conditions (Hasan et al. 2024; Bhat et al. 2023). Siderophore‐producing PGPR improve iron acquisition and suppress pathogen proliferation by limiting iron availability in the rhizosphere (Sarwar et al. 2022). In addition, ACC deaminase‐producing bacteria lower stress‐induced ethylene accumulation, thereby sustaining root elongation and photosynthetic activity during drought and salinity stress (Vocciante et al. 2022). Beneficial microbes also produce phytohormones such as indole‐3‐acetic acid (IAA), cytokinins, gibberellins, and salicylic acid that regulate root system architecture, stomatal behavior, osmotic adjustments, and antioxidant metabolism, collectively contributing to an improved stress adaptation (Aloo et al. 2023; Altaf et al. 2023). These microbial traits can be strategically targeted through microbiome engineering, microbial consortia development, and bioinoculant‐based crop management to enhance nutrient use efficiency, maintain rhizosphere stability, and improve crop resilience against combined abiotic and biotic stresses. Despite profiling advances, spatiotemporal dynamics across tissues and stress cycles remain insufficiently resolved. Longitudinal sampling, imaging, isotope tracing, and environmental integration are needed to link colonization dynamics with plant physiological responses.

Plant‐associated microbial communities are dynamically assembled through coordinated interactions among root exudates, host signaling pathways, and environmental stress cues, collectively shaping microbiome composition and function under adverse conditions. Root exudation is a primary mechanism by which plants structure rhizosphere microbiomes and dynamically reshape community composition in response to environmental cues (Robert et al. 2025). By modulating the quantity and chemistry of released metabolites, plants recruit beneficial microbes, suppress antagonists, and influence microbe–microbe interactions that feedback on host stress tolerance (Chen et al. 2024; Wankhade et al. 2025).

Abiotic stresses alter carbon allocation and the profile of sugars, organic acids, amino acids, phenolics, and secondary metabolites in the rhizosphere. Drought generally reduces total exudation but enriches osmoprotectants and antioxidants, whereas salinity often enhances organic acid release to chelate toxic ions and regulate pH (Thakar et al. 2025). These shifts act as selective filters, favoring microbes adapted to the revised chemical niche (Fracchia et al. 2024). Exudation is genotype‐dependent and influenced by development and nutrient status, with genotype × environment interactions shaping recruitment of stress‐mitigating consortia (Hafner et al. 2025; Fan et al. 2023).

Under non‐stress conditions, plant roots constitutively release a broad spectrum of metabolites including sugars, amino acids, organic acids, fatty acids, mucilage, vitamins, phenolics, flavonoids, and phytohormone‐associated compounds that collectively regulate nutrient mobilization, microbial attraction, and rhizosphere communication (Robert et al. 2025; Martins et al. 2026). These exudates support the establishment of mutualistic and commensal microbial communities involved in nutrient cycling, phytohormone production, and pathogen suppression. Under abiotic and biotic stress conditions, however, the composition and quantity of root exudates are dynamically altered to recruit stress‐adapted microbiota and enhance plant defense responses. Drought and salinity commonly stimulate the release of osmoprotective metabolites, organic acids, proline, sugars, abscisic acid‐related compounds, and antioxidant phenolics, whereas pathogen or herbivore attack often induces flavonoids, benzoxazinoids, coumarins, strigolactones, and other defense‐related secondary metabolites that selectively enrich beneficial microbial taxa (Sharma et al. 2023; Wankhade et al. 2025). Despite differences in stress specificity, many constitutive and stress‐induced exudates share common ecological functions as both carbon substrates and signaling molecules that mediate microbial recognition, chemotaxis, biofilm formation, and activation of induced systemic tolerance pathways.

The targeted manipulation of root exudate chemistry is increasingly being explored as a strategy to improve plant resilience and phytobiome stability (Korenblum et al. 2020). Breeding approaches aimed at optimizing exudation profiles, along with the application of microbial inoculants, biostimulants, and stress‐priming agents, can selectively enhance the recruitment of plant growth‐promoting rhizobacteria, arbuscular mycorrhizal fungi, and other stress‐alleviating microorganisms (Upadhyay 2025). Similarly, engineering exudate‐mediated signaling pathways may improve nutrient acquisition, ROS detoxification, osmotic adjustment, and disease resistance under adverse environmental conditions. Such approaches represent a promising avenue for developing climate‐resilient agroecosystems through deliberate rhizosphere microbiome engineering.

Beyond serving as substrates, exudates function as signaling mediators controlling recognition and compatibility (Upadhyay 2025). Flavonoids induce nodulation genes in symbionts and stimulate mycorrhizal hyphal branching, while microbial lipochitooligosaccharides activate receptor‐mediated pathways in roots (Bag et al. 2022; Kumar et al. 2024). Under stress, plants must balance symbiotic signaling with immune vigilance, as the susceptibility to opportunists increases (Pradeu et al. 2024; Hossain et al. 2025). Mutualists fine‐tune communication to maintain stress‐alleviating functions without triggering strong defenses (Gourmet et al. 2024).

The “cry for help” hypothesis proposes that stressed plants reprogram exudation to recruit beneficial partners (Wang and Song 2022; Fang et al. 2025). Selective enrichment of PGPR producing phytohormones, ACC deaminase, siderophores, or detoxifying enzymes can enhance tolerance (Vocciante et al. 2022; Shahid et al. 2023). While rapid restructuring is documented under controlled conditions (Yuan et al. 2025), consistency in complex field environments remains uncertain (Afridi et al. 2022; Nerva et al. 2022).

3.2. Microbial Mechanisms Enhancing Plant Stress Tolerance

Plant growth‐promoting rhizobzcteria (PGPR) alleviate stress through interconnected physiological and biochemical mechanisms rather than through isolated pathways. They are diverse root‐associated bacteria that enhance plant growth and resilience under adverse conditions (Sharma et al. 2025; Ansabayeva et al. 2025). These mechanisms frequently operate simultaneously under field conditions, where phytohormone modulation, antioxidant enhancement, osmotic regulation, and nutrient mobilization collectively contribute to plant resilience against combined stresses (Raza et al. 2022; Nazir et al. 2024; Figure 3).

FIGURE 3.

Mechanisms of PGPR‐mediated stress tolerance and arbuscular mycorrhizal associations in plant stress mitigation. The illustration depicts two complementary microbial strategies for enhancing plant abiotic stress resilience. Left panel—PGPR‐mediated stress tolerance: Plant growth‐promoting rhizobacteria colonize the root surface as biofilms and confer stress protection through direct mechanisms (N₂ fixation, phosphate solubilization, siderophore‐mediated Fe³⁺ chelation, IAA production, and ACC deaminase‐mediated ethylene reduction) and indirect mechanisms (biocontrol via antibiotics and lytic enzymes, induced systemic resistance (ISR) through JA/ET signaling, EPS‐mediated heavy metal sequestration (As³⁺, Cd²⁺, Pb²⁺), and growth‐promoting VOC emission). Right panel—Mycorrhizal stress mitigation: Arbuscular mycorrhizal fungi (AMF) colonize root cortical cells, forming arbuscules for bidirectional phosphorus–carbon exchange. Extraradical hyphae extend nutrient and water acquisition beyond the root depletion zone, produce glomalin for soil aggregate stabilization, sequester toxic metals in fungal vacuoles, enhance host ROS scavenging, and establish common mycorrhizal networks (CMNs) for inter‐plant resource and signal transfer. Center: Synergistic PGPR–AMF interactions are indicated, where helper bacteria enhance mycorrhizal colonization and vice versa, providing additive stress protection.

Many PGPRs synthesize or modulate indole‐3‐acetic acid (IAA), cytokinins, gibberellins, and abscisic acid (ABA), thereby influencing root architecture, shoot growth, and stomatal behavior. IAA‐producing strains enhance lateral root formation and root hair development, improving nutrient and water uptake under stress (Bhat et al. 2023; Feng et al. 2024). Regulation of cytokinins and gibberellins sustains shoot growth, while ABA‐producing or ABA‐modulating microbes improve stomatal control and water‐use efficiency under drought and salinity (Chen et al. 2023; Ali et al. 2020). Hormonal outcomes depend on developmental stage and hormone balance (Van de Poel et al. 2015; Jan et al. 2024).

Stress‐induced ethylene often suppresses growth and accelerates senescence (Baharudin and Osman 2023). PGPR with ACC deaminase degrade 1‐aminocyclopropane‐1‐carboxylate (ACC), lowering ethylene levels and alleviating growth inhibition (Gamalero et al. 2023). This sustains root elongation and cell division under moderate stress (Kurepa and Smalle 2023).

PGPRs produce compatible solutes (e.g., proline, trehalose), antioxidants, and exopolysaccharides (EPS), contributing to the osmotic adjustment and reactive oxygen species (ROS) detoxification. EPS‐mediated biofilm formation creates hydrated microenvironments that protect roots from desiccation and ionic stress (Renganathan et al. 2025). PGPR also stimulate plant antioxidant systems and osmolyte accumulation, stabilizing membranes and enzymes under severe stress (Ali et al. 2022; Sahu et al. 2022; Teiba et al. 2023).

Abiotic stress limits nutrient diffusion and uptake (Kumari et al. 2022; Bisht et al. 2023). Nitrogen‐fixing PGPR supply reduced nitrogen (Pradhan et al. 2025), phosphate‐solubilizing bacteria mobilize unavailable phosphorus (Ibrahim et al. 2022; Zhu et al. 2024), and siderophore producers enhance iron acquisition while restricting pathogen access (Sarwar et al. 2022).

PGPR‐induced systemic resistance (ISR) primes defense pathways, enabling faster and stronger responses to subsequent stress while minimizing energy costs (Zhu et al. 2022; Ali et al. 2024). ISR may confer cross‐tolerance in multi‐stress environments (Kamran et al. 2025), though growth–defense trade‐offs remain unclear (Guo et al. 2023). Despite a broad mechanistic potential, PGPR efficacy is context‐dependent, varying with soil, climate, genotype, and microbial competition (Al‐Turki et al. 2023; Philippot et al. 2024). Integrating strain traits with ecological and environmental parameters into trait‐based predictive frameworks is essential for predicting field performance under variable environmental conditions.

3.3. Mycorrhizal Networks and Functional Stress Adaptation

Mycorrhizal fungi, particularly arbuscular mycorrhizal fungi (AMF), form symbiotic associations with most terrestrial plants and play a critical role in plant adaptation to abiotic stresses. Mycorrhizal associations extend beyond nutrient acquisition by facilitating inter‐plant communication, hydraulic redistribution, and ecosystem‐level stress buffering under fluctuating environmental conditions (Ahmed et al. 2025; Figure 3).

AMF colonize root cortical cells and form arbuscules that enable a bidirectional exchange of nutrients and carbon (Duan et al. 2024). Their extraradical hyphae extend beyond root depletion zones, accessing nutrients unavailable to roots and improving phosphorus, micronutrient, and sometimes nitrogen uptake, particularly under drought, salinity, or soil compaction (Zhang, Liu, et al. 2023; Zhang, Xu, et al. 2023). Mycorrhizal colonization also enhances osmotic adjustments, modulates phytohormones such as ABA and jasmonates (Cao et al. 2025), and increases antioxidant activity, helping maintain photosynthesis and biomass production under stress (Faria et al. 2023).

Common mycorrhizal networks (CMNs) connect multiple plants, enabling transfer of nutrients and potentially signaling molecules. These networks may redistribute resources from less stressed to more stressed plants or transmit warning signals that prime neighboring individuals against stress (Karimi‐Jashni and Yazdanpanah 2023; Ullah et al. 2024). Such interactions enhance community‐level resilience and contribute to a spatial buffering under heterogeneous environmental stress (Rillig et al. 2025; Mony et al. 2024).

Mycorrhizal networks may also facilitate hydraulic redistribution by transferring water from deeper moist soil layers to drier zones via interconnected hyphae and roots (Antunes 2025). This process improves local moisture availability, stabilizes plant water status, delays stomatal closure, and sustains carbon assimilation during early drought phases (Sha et al. 2024; Sun et al. 2025; Sharma et al. 2021), thereby reducing negative impacts on growth and reproduction (Diagne et al. 2020).

3.4. Synergistic Interactions Between PGPR and Mycorrhizal Fungi Under Stress

Recent studies indicate that plant stress resilience is often enhanced more effectively by cooperative microbial consortia than by single microbial inoculants alone (Santoyo et al. 2021; Compant et al. 2019). Synergistic interactions between PGPR and AMF improve rhizosphere functioning through complementary physiological and ecological mechanisms. PGPR can stimulate AMF spore germination, hyphal growth, and root colonization through the production of signaling molecules, siderophores, vitamins, and extracellular enzymes, while AMF improve root surface area and carbon flow, thereby creating favorable niches for bacterial proliferation (Frey‐Klett et al. 2007; Artursson et al. 2006).

Under drought and salinity stress, PGPR–AMF consortia frequently enhance plant performance through a coordinated regulation of osmolyte accumulation, antioxidant activity, nutrient uptake, and hormonal homeostasis. AMF improve phosphorus and water acquisition through extensive extraradical hyphal networks, whereas PGPR contribute through nitrogen fixation, phosphate solubilization, ACC deaminase activity, and exopolysaccharide‐mediated rhizosphere stabilization. In maize ( Zea mays L.), combined PGPR–AMF inoculation has been reported to improve root hydraulic conductivity, maintain photosynthetic efficiency, and reduce oxidative damage more effectively than individual inoculants under drought and salinity stress conditions (Begum et al. 2019).

Synergistic microbial interactions also influence stress‐responsive signaling pathways and immune priming. Combined inoculation has been shown to modulate abscisic acid, jasmonic acid, salicylic acid, and ethylene signaling networks, thereby improving induced systemic resistance and metabolic plasticity under combined abiotic and biotic stress conditions. In addition, microbial consortia can enhance soil aggregation, carbon stabilization, and rhizosphere resilience, contributing to long‐term ecosystem stability under climate change scenarios (Barea et al. 2005; Singh et al. 2023).

Despite these advantages, the effectiveness of PGPR–AMF interactions remains strongly influenced by plant genotype, soil physicochemical properties, climatic variability, and microbial compatibility. Future research should prioritize the development of synthetic microbial communities (SynComs), which are rationally designed consortia of functionally complementary microorganisms assembled to provide stable and predictable plant benefits under diverse environmental conditions. Compared with single‐strain inoculants, SynComs offer greater ecological stability, functional redundancy, and resilience against multiple concurrent stresses. Their design should be guided by functional trait‐based selection (e.g., ACC deaminase activity, nutrient solubilization, phytohormone production, and antioxidant induction) and integrated with multi‐omics approaches to identify key microbial interactions and optimize community performance. Together, these strategies will improve the predictability, reproducibility, and field‐level consistency of microbiome‐assisted stress management in climate‐resilient agriculture.

4. Multi‐Stress Tolerance: Synergistic and Antagonistic Interactions

In agroecosystems, simultaneous stresses such as drought, heat, salinity, nutrient deficiency, pollutants, and biotic pressures interact in non‐additive ways, producing either synergistic effects that intensify damage, or antagonistic effects, where one stress partially offsets another. Understanding these interactions is essential for accurate performance prediction, climate‐resilient breeding, and microbiome engineering under field conditions (Amin et al. 2025; Misu et al. 2025). Current research highlights the need for predictive frameworks capable of integrating complex stress combinations rather than extrapolating from single‐stress responses (Zhang et al. 2024; Varadharajan et al. 2025; Figure 4).

FIGURE 4.

Abiotic–biotic stress cross‐talk in plants: Synergistic and antagonistic hormonal interactions governing multi‐stress tolerance. The illustration depicts the convergence of abiotic stresses (drought, salinity, heat, cold, heavy metals) and biotic stresses (bacterial, fungal, and viral pathogens; herbivory) on a central hormonal signaling network within the plant. Five major phytohormones, abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA), ethylene (ET), and auxin/cytokinin, form interconnected nodes with synergistic (green solid arrows: ABA–JA, ET–JA), antagonistic (red dashed lines: ABA–SA, SA–JA, auxin–SA), and context‐dependent (orange dotted lines: ET–SA) interactions. These cross‐talk pathways regulate downstream transcription factor families (DREB/CBF, WRKY, MYC2, ERF, NAC, bZIP/AREB), which orchestrate stress‐specific and shared defense outputs. Combined stress scenarios illustrate hormonal conflicts: Drought suppresses SA‐mediated pathogen defense via ABA dominance, while salinity–herbivory combinations create resource allocation trade‐offs partially compensated by JA–ABA synergy. Convergence points shared across both stress types, including ROS signaling, MAPK cascades, calcium waves, epigenetic modifications, small RNAs, and stress priming/memory, are shown as a common response platform enabling cross‐tolerance.

Plants exposed to multiple abiotic stresses such as drought, salinity, heat, and oxidative stress often exhibit a set of common physiological and molecular responses associated with cellular homeostasis and survival. The maintenance of tissue potassium (K⁺) retention has emerged as a critical determinant of stress tolerance because K⁺ plays central roles in osmotic regulation, stomatal conductance, enzyme activation, and maintenance of membrane potential under stress conditions (Shabala and Pottosin 2014). Similarly, the preservation of cellular energy homeostasis through efficient ATP generation, mitochondrial stability, and metabolic flexibility enables plants to sustain growth and defense processes during prolonged stress exposure (Baena‐González and Sheen 2008). Stress adaptation is further coordinated through conserved signaling pathways involving calcium signaling, ABA‐mediated responses, ROS signaling, and stress‐responsive transcriptional networks. Several gene families, including dehydration‐responsive element‐binding proteins (DREB/CBF), NAC, WRKY, bZIP, and heat shock proteins (HSPs), regulate osmotic adjustments, antioxidant defense, protein stabilization, and stress‐responsive gene expression under combined stress conditions (Ramegowda and Senthil‐Kumar 2015; Zhu 2016). In addition, ion transport‐related genes such as SOS1 (Salt Overly Sensitive 1), NHX (Na⁺/H⁺ exchangers), and HKT (High‐Affinity K⁺ Transporters) contribute significantly to ion homeostasis and salinity adaptation by regulating Na⁺ exclusion, vacuolar Na⁺ sequestration, Na⁺/K⁺ balance, and cellular compartmentalisation under salt stress conditions (Zhu 2003; Munns and Tester 2008; Deinlein et al. 2014). Collectively, these interconnected physiological traits and molecular networks represent promising targets for developing climate‐resilient crops with a broad‐spectrum tolerance to multiple environmental stresses.

4.1. Physiological and Molecular Responses to Combined Stresses

Concurrent abiotic stresses reshape plant signaling, physiology, and metabolism beyond individual stress effects. Combinations such as drought × heat or salinity × temperature generate distinct transcriptional and metabolic profiles that cannot be predicted from isolated treatments, largely due to competing demands on water status, carbon allocation, and redox balance (Xalxo et al. 2020; Zhang, Liu, et al. 2023; Zhang, Xu, et al. 2023).

Drought and heat commonly co‐occur under climate change, jointly impairing photosynthesis, membrane stability, and reproductive processes (Pang et al. 2025; Priya et al. 2025). Drought promotes stomatal closure to conserve water, limiting carbon fixation while activating osmotic and antioxidant defenses (Wang et al. 2016; Haghpanah et al. 2024). In contrast, heat stress increases the cooling demand and destabilizes cellular structures (Ul Hassan et al. 2022). Their combination creates a trade‐off between water conservation and heat dissipation, resulting in stricter stomatal regulation, accelerated senescence, and yield loss. This interaction induces unique transcriptional responses, ROS dynamics, and hormonal shifts, while microbiome contributions remain insufficiently understood (Haghpanah et al. 2024; Chachar et al. 2025; Li, Geng, et al. 2025; Li, Sun, et al. 2025). Recent studies have demonstrated that crop responses to combined drought and heat stress are highly species‐ and genotype‐dependent. In wheat ( Triticum aestivum L.), combined terminal heat and water deficit during grain filling significantly reduced photosynthetic efficiency, pollen viability, and grain weight compared with either stress alone (Priya et al. 2025). Similarly, field‐grown maize exposed to simultaneous drought and high‐temperature episodes showed altered stomatal conductance, reduced maximum quantum efficiency of PSII (Fv/fm), decreased effective quantum yield of PSII [ΦPSII; Y(II)], and accelerated senescence, ultimately reducing photosynthetic performance and yield stability (Lesk et al. 2022; Liang, Yu, Ju, et al. 2025; Liang, Yu, Meng, et al. 2025). In rice, drought × heat interactions during reproductive stages disrupted spikelet fertility and carbohydrate partitioning, particularly under low soil moisture and elevated nighttime temperature conditions (Li et al. 2024). However, resilience was improved in stress‐adapted genotypes possessing stronger antioxidant defense systems, enhanced osmolyte accumulation, and deeper root architecture, which collectively contribute to improved water acquisition, cellular protection, and maintenance of photosynthetic activity under combined drought and heat stress (Ramegowda and Senthil‐Kumar 2015; Zandalinas et al. 2020; Li et al. 2024). Furthermore, the strategic manipulation of these adaptive traits through microbiome‐assisted breeding, targeted application of phytohormones, and precision irrigation management has emerged as a promising approach for enhancing crop resilience and sustaining productivity under future climate‐change scenarios (Compant et al. 2019; Vishwakarma et al. 2017; Ullah et al. 2025).

Recent experimental evidence further demonstrates that crop responses to combined salinity and temperature stress are strongly influenced by genotype‐specific physiological traits and rhizosphere microbial associations. Salt‐tolerant cultivars generally maintain higher K⁺/Na⁺ ratios, stronger antioxidant defense systems, and better photosynthetic stability under elevated temperature conditions compared with sensitive genotypes. Moreover, inoculation with plant growth‐promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) have been shown to improve ion homeostasis, osmotic adjustment, nutrient acquisition, and reactive oxygen species detoxification under combined salinity–heat stress, thereby enhancing plant growth and productivity. These findings indicate that integrating stress‐tolerant germplasm with microbiome‐based interventions represents a promising strategy for improving crop resilience under compound environmental stresses (Zandalinas et al. 2020; Begum et al. 2019; Vurukonda et al. 2016). Salinity causes osmotic stress and ionic toxicity, whereas temperature extremes disrupt membrane function and enzymatic activity. Plants respond through ion regulation, compatible solute accumulation, and enhanced antioxidant activity (Joshi et al. 2022; Ali et al. 2022). High temperatures often intensify ionic toxicity by increasing membrane permeability and altering transporter activity, leading to oxidative stress and reproductive decline (von Weissenberg et al. 2022). Conversely, lower temperatures may reduce ion uptake and partially mitigate toxicity (Xu et al. 2022). Outcomes depend on stress intensity, timing, genotype, and microbiome composition (Ullah et al. 2025). Salinity and temperature extremes often co‐occur in irrigated and coastal agroecosystems, particularly affecting rice, tomato, and chickpea cultivation. In rice‐growing coastal regions, elevated salinity combined with high temperature reduced root hydraulic conductivity and disrupted ion homeostasis through excessive Na + accumulation (Joshi et al. 2022; Li et al. 2024). Tomato plants subjected to salinity × heat stress under greenhouse conditions exhibited severe oxidative damage and membrane instability, whereas inoculation with plant growth–promoting rhizobacteria (PGPR) improved antioxidant activity and nutrient uptake, leading to enhanced biomass retention (Hasan et al. 2024). Likewise, chickpeas exposed to saline soils under elevated temperature regimes showed improved stress tolerance when associated with arbuscular mycorrhizal fungi (AMF), owing to enhanced phosphorus uptake and osmotic adjustments. These findings indicate that manipulation of root‐associated microbiomes, combined with salt‐tolerant cultivars and optimized irrigation management, can substantially improve crop performance under compound salinity–temperature stress.

Field conditions frequently involve three or more simultaneous stresses. Multifactorial studies show emergent responses that cannot be predicted from dual‐stress experiments. In major cereal systems such as rice and wheat, multifactorial stress combinations involving drought, heat, and heavy metal toxicity are becoming increasingly common under climate change and anthropogenic contaminations. These combined stresses impose synergistic effects on membrane stability, photosynthetic efficiency, nutrient uptake, and reproductive development beyond those observed under individual stresses. For example, drought and heat stress can enhance heavy metal accumulation in plants by increasing root membrane permeability, altering transpiration‐driven metal transport, and modifying rhizosphere physicochemical properties that influence metal bioavailability (Rizwan et al. 2017). These changes often lead to greater uptake and translocation of toxic metals, resulting in excessive reactive oxygen species (ROS) generation, disruption of cellular redox homeostasis, impairment of photosynthetic machinery, and widespread metabolic dysfunction (Zandalinas et al. 2020; Rizwan et al. 2017). At the mechanistic level, these stress combinations trigger an excessive reactive oxygen species (ROS) generation, perturb mitochondrial and chloroplast electron transport chains, and activate complex hormonal cross‐talk involving abscisic acid (ABA), ethylene, salicylic acid (SA), and jasmonic acid (JA). Plants respond through coordinated antioxidant defense systems, osmolyte accumulation, heat‐shock proteins, metal chelation, and stress‐responsive transcriptional networks (Rizhsky et al. 2004; Suzuki et al. 2014). Emerging evidence further indicates that stress‐adapted rhizosphere microbiomes and plant growth‐promoting microorganisms can mitigate multifactorial stress impacts by improving ion homeostasis, antioxidant capacity, phytohormone balance, and heavy metal immobilization in the rhizosphere. These findings highlight the importance of integrating plant physiology, microbiome engineering, and multi‐omics approaches to improve crop resilience under realistic field‐level stress scenarios (Zandalinas et al. 2020). Heavy metals may weaken antioxidant defenses, increasing vulnerability to drought or heat, while nutrient limitation restricts synthesis of protective metabolites (Rao and Zheng 2025; Tariq et al. 2023). Antagonistic responses may arise through shared hormonal or antioxidant pathways, emphasizing the need for systems‐level approaches (Aloo et al. 2023; Altaf et al. 2023).

Most current predictive models assume additive stress effects and therefore fail to represent the complex interplay among signaling cross‐talk, metabolic trade‐offs, and plant–microbiome interactions. Since high‐throughput phenotyping and omics datasets are largely derived from single or dual stresses, predictive accuracy under field conditions remains limited. Addressing this gap requires controlled multifactorial experiments, advanced phenotyping, and computational tools such as network analysis and machine learning (Table 2) to support breeding and microbiome‐based resilience strategies.

TABLE 2.

Emerging technologies for holobiont engineering.

Technology platform	Innovations in multi‐stress resilience	Translational constraints	References
CRISPR and genome editing	Precision editing of host stress loci and microbial traits (e.g., ACC deaminase). Base and prime editing for fine‐tuning regulatory elements.	Fragmented global biosafety regulations. Potential risks of horizontal gene transfer.	Kumar et al. (2023), Alharbi et al. (2024)
Synthetic biology	Programmable holobionts via engineered interkingdom signaling. Synthetic biosensors for real‐time stress detection. Ecological memory systems for stress priming.	Maintaining genetic stability and functional resilience under competitive, non‐sterile field conditions.	Zhang, Liu, et al. (2023), Zhang, Xu, et al. (2023), Portal‐Gonzalez et al. (2025)
AI and machine learning	Multi‐omics integration to predict plant‐microbe‐stress outcomes. Network analysis to optimize Synthetic Microbial Communities (SynComs).	Dataset heterogeneity and varying sequencing pipelines. Lack of standardized data harmonization protocols.	De Souza et al. (2020), Kumar et al. (2023)
Nanotechnology	Nano‐encapsulation for targeted inoculant, nutrient, and ROS‐scavenger delivery. Nanoscale biosensors for spatiotemporal rhizosphere monitoring.	Assessing long‐term environmental persistence and nanotoxicity. Unintended broader ecosystem impacts.	Isibor et al. (2024), Rajpal et al. (2025)

Abiotic and biotic stresses frequently co‐occur in agroecosystems, creating complex interactions between stress‐response and immune pathways. Drought, nutrient imbalance, and temperature extremes often coincide with pathogen attack or herbivory (Singh et al. 2023), producing either cross‐tolerance (Lesk et al. 2022) or trade‐offs between abiotic adaptation and immunity (Leisner et al. 2023). The plant microbiome further modulates these outcomes by reshaping signaling and metabolic responses (Ullah et al. 2025).

Cross‐tolerance arises when activation of one stress‐response pathway enhances resilience to additional stresses through shared signaling networks or overlapping downstream mechanisms. For example, drought‐induced ABA and ROS can prime transcription factors and antioxidant systems that also reinforce pathogen resistance (Prakash et al. 2024). Mild heat stress induces heat shock proteins and chaperones that protect against thermal injury and certain pathogen toxins (Yang et al. 2022; Francis et al. 2025). Cross‐tolerance mechanisms have been widely documented in cereals and legumes exposed to sequential or simultaneous stresses. For example, drought‐preconditioned maize plants exhibited enhanced tolerance to subsequent pathogen infection through elevated ABA‐mediated antioxidant responses and primed defense signaling pathways (Ramegowda and Senthil‐Kumar 2015). In soybean, mild osmotic stress induced accumulation of osmoprotectants and stress‐responsive transcription factors that subsequently improved tolerance against heat and oxidative stress under controlled environmental conditions (Praveen et al. 2023). Rice plants colonized by beneficial Bacillus and Pseudomonas strains showed stronger induced systemic resistance (ISR), improved ROS scavenging, and maintenance of photosynthetic activity during combined salinity and pathogen stress. Such responses demonstrate that stress priming, microbial inoculation, and targeted hormonal regulation can be strategically manipulated to activate broad‐spectrum resilience pathways in crops exposed to multifactorial stress conditions.

Several stress‐responsive transcription factors (TFs) act as central regulators linking abiotic adaptation with biotic defense responses. Members of the WRKY family, particularly WRKY33, WRKY40, and WRKY70, are strongly induced under drought, salinity, and oxidative stress and regulate defense‐associated genes involved in salicylic acid (SA) and jasmonic acid (JA) signaling pathways, thereby enhancing resistance against fungal and bacterial pathogens (Chen et al. 2017; Birkenbihl et al. 2017). NAC transcription factors such as SNAC1 and ANAC019 contribute to drought and heat tolerance through stomatal regulation, ROS detoxification, and activation of defense‐related metabolites, while also modulating pathogen‐responsive signaling networks (Nuruzzaman et al. 2013). Similarly, dehydration‐responsive element‐binding proteins (DREB2A and DREB1A) improve osmotic stress tolerance and stimulate downstream protective genes associated with antioxidant defense and stress memory (Sakuma et al. 2006). MYB and bZIP transcription factors further coordinate flavonoid biosynthesis, ABA‐dependent signaling, and cellular redox homeostasis, thereby strengthening immunity under combined stress conditions (Ambawat et al. 2013; Alves et al. 2013). Ethylene‐responsive factors (ERFs), particularly ERF1 and ORA59, integrate JA–ethylene cross‐talk and activate pathogenesis‐related proteins that enhance tolerance to necrotrophic pathogens during abiotic stress exposure (Müller and Munné‐Bosch 2015). Collectively, these transcriptional regulators function as molecular hubs that integrate hormonal, oxidative, and defense signaling pathways to promote cross‐tolerance under multifactorial stress environments.

Beneficial microbes, including plant growth–promoting rhizobacteria (PGPR) and mycorrhizal fungi, enhance cross‐tolerance via induced systemic resistance (ISR), hormonal modulation, and improved nutrient uptake (Mashabela et al. 2022; Pandey et al. 2023). However, responses remain context dependent, varying with stress intensity and duration (Kamran et al. 2025). PGPR and beneficial soil microbes play a central role in nutrient acquisition and phytobiome resilience under degraded and stress‐prone environments. Several microbial genera including Pseudomonas, Bacillus, Rhizobium, Azotobacter, and Azospirillum enhance nutrient availability through biological nitrogen fixation, phosphate solubilization, potassium mobilization, and siderophore‐mediated micronutrient acquisition. Phosphate‐solubilizing bacteria such as Bacillus megaterium and Pseudomonas fluorescens release organic acids and phosphatases that convert insoluble phosphorus into plant‐available forms, whereas diazotrophic microbes like Azotobacter chroococcum and Azospirillum brasilense contribute significantly to nitrogen enrichment in the rhizosphere. In addition, AMF, particularly species of Glomus, improve nutrient and water uptake by extending the effective root surface area and facilitating phosphorus transport under nutrient‐deficient conditions (Backer et al. 2018). Many PGPR also synthesize phytohormones such as indole‐3‐acetic acid (IAA), produce ACC deaminase, and stimulate antioxidant defense systems, thereby improving root architecture, nutrient uptake efficiency, and tolerance to abiotic stresses (Glick 2012; Richardson et al. 2009). These multitrophic microbial interactions collectively contribute to soil fertility restoration, nutrient cycling, and enhanced climate resilience in conservation and degraded agroecosystems.

Abiotic and biotic stresses converge on central signaling hubs such as MAPK cascades, ROS bursts, Ca²⁺ fluxes, and phytohormones including ABA, SA, JA, and ethylene. These nodes integrate diverse cues to shape coordinated responses. Drought‐induced ABA can suppress SA‐mediated defense against biotrophs (Leisner et al. 2023; Verma et al. 2025) while promoting JA/ethylene pathways effective against necrotrophs. Conversely, pathogen attacks can alter ABA signaling and stomatal regulation, influencing subsequent drought or salinity responses (Du et al. 2024).

Mild abiotic stress can prime plants for enhanced defense against later challenges (Praveen et al. 2023). Priming involves partial pathway activation, accumulation of latent transcription factors, epigenetic modifications, and maintenance of poised chromatin states at defense loci (Mishra and Ivashkiv 2024). These changes enable faster and amplified responses and may sometimes be heritable. Beneficial microbes also induce priming via ISR (Yu et al. 2022), although prolonged or constitutive activation of ISR may impose substantial metabolic and physiological costs on plants. Sustained defense readiness requires continuous allocation of energy, carbon skeletons, amino acids, and reducing power toward the biosynthesis of defense proteins, phytoalexins, antioxidants, and signaling metabolites, often at the expense of growth, photosynthetic efficiency, and reproductive investment (Huot et al. 2014; Karasov et al. 2017). Persistent activation of jasmonic acid–, salicylic acid–, and ethylene‐mediated signaling networks may further disrupt hormonal homeostasis and resource partitioning, particularly under chronic or low‐intensity stress conditions where defense expenditure may exceed adaptive benefits (Heil and Baldwin 2002; Guo et al. 2023). From our perspective, ISR‐mediated priming is most beneficial when it remains inducible and transient rather than constitutively active, as dynamic regulation enables plants to balance stress preparedness with optimal growth and productivity under fluctuating environmental conditions.

Plant‐associated microbiomes undergo significant restructuring under multifactorial stress environments, with distinct crop‐specific recruitment patterns. In drought‐stressed maize rhizospheres, enrichment of Actinobacteria and Bacillus spp. was associated with improved osmoprotection and root growth maintenance under field moisture deficit conditions (Nazari et al. 2023). Rice cultivated under saline and waterlogged soils showed increased abundance of sulfur‐reducing and halotolerant microbial taxa that contributed to nutrient cycling and ionic balance (Misu et al. 2025). Similarly, wheat plants grown under combined heat and nutrient stress recruited microbial communities capable of phytohormone production and ACC deaminase activity, thereby reducing ethylene‐mediated growth inhibition. Manipulation of microbiome assembly through seed coating, synthetic microbial consortia, organic amendments, and rhizosphere engineering may therefore provide an effective strategy for stabilizing crop productivity under climate‐induced stress combinations (Compant et al. 2019; De Souza et al. 2020).

4.2. Nanotechnology‐Assisted Delivery Systems and Biosensing Platforms for Precision Plant–Microbiome Management

Recent advances in nanotechnology and biosensing are expanding the scope of microbiome engineering for climate‐resilient agriculture by enabling precise delivery, monitoring, and regulation of plant–microbe interactions under complex stress environments. Conventional microbial inoculants often suffer from poor survivability, limited rhizosphere colonization, and inconsistent field performance due to environmental fluctuations such as drought, salinity, temperature stress, and soil heterogeneity. Nanotechnology‐assisted delivery systems provide innovative solutions to these limitations through the development of nanoformulations, encapsulated microbial carriers, and controlled‐release systems that enhance microbial stability and targeted delivery within the rhizosphere (Kah et al. 2019; Shang et al. 2019).

Nanomaterials such as chitosan nanoparticles, silica nanoparticles, liposomes, nanoemulsions, and polymeric nanocarriers can protect beneficial microorganisms and bioactive compounds from environmental degradation while improving adherence to plant roots and facilitating gradual release of nutrients or signaling molecules. These systems can also enhance the efficiency of plant growth‐promoting rhizobacteria (PGPR), mycorrhizal inoculants, and biostimulants by improving their persistence and functional activity under abiotic stress conditions. In addition, nano‐enabled delivery of phytohormones, antioxidants, osmoprotectants, and micronutrients has shown considerable potential in mitigating oxidative stress, maintaining cellular homeostasis, and enhancing stress‐responsive signaling pathways in plants (Raliya et al. 2018; Usman et al. 2020).

Alongside nanotechnology, biosensing platforms are emerging as important tools for real‐time monitoring of plant physiological status and rhizosphere dynamics. Advanced biosensors integrating nanomaterials, electrochemical detection systems, and wireless technologies can detect stress biomarkers, nutrient fluctuations, microbial metabolites, phytohormones, and reactive oxygen species with high sensitivity and rapid response times. Such technologies provide opportunities for early stress diagnosis and precision management in climate‐smart agriculture systems (Shang et al. 2019). Integration of biosensors with artificial intelligence, Internet of Things (IoT)‐based monitoring, and predictive analytics may further support data‐driven decision‐making for optimizing microbial interventions and improving crop resilience under multiple concurrent stresses.

4.3. Microbiome Dynamics Under Multi‐Stress Conditions

The plant‐associated microbiome is highly dynamic and responds strongly to interacting abiotic and biotic stresses. Multifactorial stress regimes can restructure microbial communities, modify functional capacities, and alter interaction networks among microbes and between microbes and the host plant (Gao et al. 2022; Manzanera 2025). Such reorganization may enhance holobiont resilience by recruiting stress‐adapted taxa or, conversely, destabilize plant–microbiome interactions, thereby influencing crop performance under field conditions.

Combined stresses frequently produce microbiome configurations distinct from single‐stress conditions. Stress combinations such as drought × heat or salinity × heat tend to select taxa capable of tolerating osmotic and thermal stress, forming stable biofilms, and maintaining antioxidant activity (Dildar et al. 2025). These conditions may enrich plant growth–promoting rhizobacteria (PGPR) and extremotolerant fungi, but declining plant health can also enable opportunistic pathogens or saprophytes to proliferate (Zenteno‐Alegría et al. 2024). Multi‐stress exposure often reduces microbial diversity and evenness, lowering functional redundancy and increasing vulnerability to disturbance, although impacts depend on which functional groups are retained (Pedrinho et al. 2024; Shin et al. 2022).

Functional redundancy—where multiple taxa perform similar ecological roles—supports microbiome stability under stress by maintaining key processes despite compositional shifts (Ramond et al. 2025; Lin et al. 2025). Functions such as nitrogen fixation, phosphorus solubilization, osmolyte production, and antioxidant activity can buffer plant–microbiome systems during combined stresses (Zhang et al. 2025). However, redundancy is uneven; specialized symbioses and host‐specific signaling pathways depend on limited taxa, and their loss may substantially reduce resilience even when general functions persist (Yang et al. 2025; Dubé et al. 2025).

Microbiome assembly history strongly influences responses to multi‐stress environments. Early colonizers can shape niche availability, resource distribution, and root exudation patterns, thereby affecting subsequent microbial recruitment (Suteau et al. 2025). For instance, prior drought exposure may promote drought‐adapted PGPR that enhance root architecture and osmotic balance during later stresses, whereas early pathogen establishment can hinder beneficial recruitment and create maladaptive outcomes (Chen et al. 2025; Adedayo and Olorunkosebi 2025). Managing priority effects may therefore improve field resilience (Rezaee Danesh 2025).

5. Translational Challenges: From Laboratory to Field

Translating advances in plant physiology and microbiome engineering into durable field‐level climate resilience remains difficult (Riaz et al. 2025; Bursakov et al. 2025). Although controlled studies have elucidated tolerance mechanisms and beneficial microbial interventions (Meena et al. 2017), consistent agronomic performance across heterogeneous agroecosystems is uncommon (de Sousa et al. 2024). Environmental variability, overlapping stresses, and soil–plant–microbe complexity imposes strong translational constraints (Semenov et al. 2025). Addressing these gaps requires integrative, multidisciplinary frameworks linking molecular insights with ecological and management realities (Anyshchenko 2022).

5.1. Biological and Ecological Constraints in Field Translation

Despite progress in stress biology and breeding, broadly adaptable stress‐tolerant cultivars are limited. Laboratory and greenhouse studies often confirm resistance to single stresses, yet field performance (Table 3) under multifactorial conditions remains unstable (Liang, Yu, Meng, et al. 2025). Stress tolerance is a systems‐level property emerging from molecular, physiological, and ecological interactions (Satrio et al. 2024). Multiple stresses frequently converge on shared signaling networks (Zahra et al. 2023; Aryendu et al. 2025; Wang et al. 2025), complicating prediction and breeding outcomes.

TABLE 3.

Translational challenges: Bridging the laboratory‐to‐field gap.

Translational barrier	Ecological and biological drivers	Required strategic interventions	References
Genomic complexity and fitness trade‐offs	Polygenic nature of stress tolerance traits. Strong genotype × environment × management (G × E × M) interactions. Metabolic resource diversion from growth/yield to defense.	Transitioning from single‐stress lab models to multifactorial field assessments. Breeding for context‐responsive regulation rather than constitutive defense.	Anderson and Song (2020), Golan et al. (2023)
Inoculant colonization resistance	Intense environmental filtering and abiotic stress upon introduction. Strong priority effects and resource competition from indigenous taxa. Suboptimal inoculum density and formulation instability.	Developing systems‐based predictive models integrating soil diagnostics and climate projections. Optimizing dose–response relationships and matching application to plant phenology.	King and Bell (2022)
Regulatory and socioeconomic bottlenecks	Fragmented, unstandardized biosafety pathways for engineered/synthetic strains. Restrictive intellectual property (IP) regimes limiting equitable access. Inconsistent field efficacy elevating perceived economic risks for farmers.	Establishing harmonized, science‐based biosafety regulations. Promoting balanced IP frameworks and resilience subsidies. Implementing participatory, region‐specific field validation.	Ludlow et al. (2025), Kolega et al. (2026)
Methodological standardization deficits	Extreme heterogeneity in soil sterilization, stress imposition, and sequencing pipelines. Absence of universal benchmark soils and harmonized phenotyping metrics.	Widespread adoption of structured data harmonization protocols (e.g., STREAMS). Establishing reference microbial consortia and standardized multi‐stress assays.	Bernardin et al. (2025)

Stress tolerance is predominantly polygenic and quantitative. Traits such as drought, salinity, and heat tolerance depend on coordinated regulation of gene families controlling ion transport, osmolyte biosynthesis, antioxidant systems, transcription factors, and hormone signaling (Dos Santos et al. 2022; Li et al. 2024). Numerous small‐effect QTLs interact epistatically, forming complex regulatory networks that limit single‐gene strategies and challenge marker‐assisted selection (Chavhan et al. 2024). Pleiotropic interactions between stress pathways and growth or reproduction further constrain simultaneous gains in tolerance and yield (Dwivedi et al. 2024; Lokeshkumar et al. 2025).

Stress expression is strongly shaped by genotype × environment × management (G × E × M) interactions. Soil moisture, temperature fluctuations, microbial communities, and nutrient availability interact with plant genetics to influence physiological responses (Muhammad et al. 2025). Agronomic practices including irrigation, fertilization, planting density, and tillage alter metabolism and rhizosphere dynamics, modifying stress outcomes (Si et al. 2023; Majumdar et al. 2025). Such context dependency produces agroecology‐specific plasticity, so genotypes performing well under controlled conditions may underperform in diverse fields (Yadav et al. 2025). Breeding must therefore integrate environmental and management variability (Cooper et al. 2022).

Laboratory studies typically impose uniform, single stresses and exclude ecological complexity (Mori et al. 2025). Field environments, however, feature fluctuating stress intensities, heterogeneous soils, and dynamic biotic interactions (Cui et al. 2024). The absence of native microbiota in controlled systems limits predictive power regarding plant–microbe interactions (Liu et al. 2025). Moreover, laboratory physiological metrics do not always translate into yield stability or grain quality under field conditions (Jan et al. 2025).

Enhanced stress tolerance often incurs metabolic trade‐offs. Sustained activation of defense pathways, osmolyte synthesis, antioxidant maintenance (Mishra et al. 2023), and protective protein production divert resources from growth and reproduction (Feng et al. 2022). Under unfavorable conditions, such reallocation may reduce biomass or yield. Traits optimized for severe stress can also impair performance under variable climates (Dong et al. 2025), underscoring the importance of flexible, context‐responsive regulation rather than constitutive defense activation. While enhancement of antioxidant machinery is widely recognized as an effective strategy for improving plant tolerance against oxidative stress, constitutive overexpression of antioxidant enzymes may also impose significant metabolic trade‐offs. Continuous activation of ROS‐scavenging pathways requires substantial allocation of carbon skeletons, ATP, reducing equivalents, and nitrogen resources, which can ultimately divert energy from growth, reproduction, and yield formation under non‐stress conditions (Mittler 2017). Excessive suppression of ROS may additionally interfere with their essential signaling functions in cellular communication, stomatal regulation, hormonal crosstalk, and stress acclimation processes (Baxter et al. 2014). Several studies have demonstrated that constitutive activation of stress‐responsive pathways may impose significant growth and yield penalties under optimal conditions due to continuous metabolic expenditure and resource diversion toward defense‐related processes. For instance, constitutive overexpression of C‐repeat binding factor/dehydration‐responsive element‐binding (CBF/DREB) genes enhanced drought and cold tolerance in Arabidopsis and wheat but frequently caused dwarfism, delayed flowering, and reduced biomass accumulation under non‐stress environments (Kasuga et al. 1999; Morran et al. 2011). Similarly, overexpression of the rice NAC transcription factor SNAC1 improved drought resistance but was associated with altered growth and reduced productivity under favorable conditions when constitutively expressed (Hu et al. 2006). Enhanced ABA‐mediated stress signaling has also been linked with reduced stomatal conductance, photosynthetic limitations, and lower yield potential in the absence of stress (Skirycz and Inzé 2010). In Arabidopsis, constitutive activation of defense pathways through salicylic acid and jasmonate signaling resulted in substantial fitness costs and reduced reproductive allocation because of continuous investment in protective metabolism (Heil and Baldwin 2002). Likewise, overexpression of stress‐associated proteins and antioxidant defense systems has been reported to improve tolerance while simultaneously restricting growth owing to carbon and energy reallocation away from primary metabolism (Feng et al. 2022). Therefore, future stress‐management strategies should focus on inducible, tissue‐specific, or stress‐responsive antioxidant regulation rather than constitutive enhancement. In this context, microbiome‐mediated approaches offer a promising and energy‐efficient alternative, as beneficial rhizospheric and endophytic microorganisms can modulate ROS homeostasis dynamically through induced systemic tolerance, phytohormone regulation, osmolyte accumulation, and activation of antioxidant enzymes only during stress exposure (Vurukonda et al. 2016; Backer et al. 2018). Such targeted and adaptive antioxidant regulation may help maintain cellular redox balance while minimizing fitness penalties and preserving crop productivity under changing environmental conditions.

Despite the demonstrated potential of plant growth–promoting microbes and synthetic microbial consortia to enhance plant stress tolerance, their field performance remains inconsistent and highly context dependent. Introduced inoculants must function within complex and competitive soil environments characterized by fluctuating moisture, nutrient gradients, and established microbial networks (Fadiji et al. 2025; Wen, Tang, et al. 2025). Unlike controlled greenhouse conditions, field soils impose ecological resistance, resulting in discrepancies between experimental success and practical outcomes. These failures are often attributed to ecological complexity, formulation limitations, soil heterogeneity, and the inadequate predictive understanding of inoculant behavior (Ahmed et al. 2024).

Successful inoculation requires microbial survival during storage, application, and early establishment in soil (O'Callaghan et al. 2022; da Cunha et al. 2023). After introduction, inoculants encounter abiotic stresses including desiccation, temperature fluctuations, osmotic stress, UV exposure, and nutrient limitations (Yan et al. 2025). Native microbial populations, already adapted to local physicochemical conditions, frequently outcompete introduced strains through environmental filtering (Zhao et al. 2026). Additionally, stress‐induced shifts in root exudation patterns can reduce carbon availability necessary for microbial persistence (Sharma et al. 2023), limiting stable rhizosphere colonization and reducing stress‐alleviating functions.

The rhizosphere represents a highly competitive ecological niche where microorganisms compete for carbon, nutrients, and spatial occupancy. Established communities exert strong priority effects, restricting the establishment of later‐arriving inoculants (Debray et al. 2022; Hu et al. 2025). Native taxa often exhibit functional redundancy and strong integration within plant–soil systems (Li, Geng, et al. 2025; Li, Sun, et al. 2025). Antagonistic interactions, including antibiotic production, siderophore‐mediated iron competition, quorum‐sensing interference, and predation by protists and bacteriophages, further reduce inoculant persistence (Bulannga and Schmidt 2023), processes rarely captured under sterile experimental conditions.

Inoculant effectiveness depends on achieving adequate microbial density at the root–soil interface. Suboptimal populations may fail to establish, while excessive inoculum increases costs and may disrupt native microbial balance (Burns 2023; Ladau et al. 2025). Application timing relative to plant developmental stage and stress onset also influences performance (Ndlazi et al. 2026). Furthermore, formulation stability, carrier materials, storage conditions, and delivery methods significantly affect microbial viability at application (Parveen et al. 2023).

Soil properties strongly regulate microbial persistence and activity. Soil pH influences enzyme function and nutrient availability (Abay et al. 2024), while salinity imposes osmotic stress that restricts microbial growth. Soil texture controls pore structure, water retention, and oxygen diffusion, thereby affecting microbial movement and establishment (Pot et al. 2022). Organic matter availability alters carbon supply and competitive dynamics, and seasonal variations in temperature and moisture further influence microbial activity and gene expression (Bogati and Walczak 2022; Majumdar and Bose 2018), limiting generalization across environments. The transition from laboratory‐scale discoveries to field‐level implementation remains constrained by ecological variability, microbial establishment failures, genotype‐dependent responses, and inconsistencies in regulatory and commercialization frameworks.

5.2. Regulatory, Economic, and Standardization Challenges

Even when biological constraints are addressed, regulatory and socioeconomic factors strongly shape the deployment of microbiome technologies (Hukic and Hukić 2025). Agricultural innovation operates within policy, intellectual property (IP), and market systems that determine accessibility, scalability, and adoption (Degila et al. 2023). Microbiome‐based products must therefore satisfy regulatory approval, demonstrate economic value, and secure social acceptance to achieve meaningful impact.

Regulatory systems for microbial inoculants vary widely across countries and often lack standardized provisions for synthetic consortia or genetically modified strains (dos Reis et al. 2024). Approval typically requires verification of strain identity, biosafety, and agronomic efficacy, while CRISPR‐edited microbes may undergo additional biosafety assessments (Saffari Natanzi et al. 2025). Lengthy and uncertain approval timelines can delay commercialization and discourage private investment. Harmonized, science‐based regulations that balance risk management with innovation are therefore essential to enable responsible scaling.

IP regimes governing microbial strains, engineered constructs, and formulations influence both innovation incentives and equitable access. Although patents stimulate research investment, restrictive licensing may constrain affordability, particularly for smallholder farmers in climate‐vulnerable regions. Ethical concerns regarding ownership of microbial genetic resources and benefit‐sharing from biodiversity‐rich ecosystems remain insufficiently addressed (Nelliyat et al. 2024). Balanced IP frameworks that protect innovation while ensuring accessibility are critical for fair dissemination and global equity.

Farmer adoption depends on demonstrable and consistent economic returns under variable climatic conditions. Microbial technologies must reliably stabilize or enhance yields to offset input costs (Konzock and Nielsen 2024). Inconsistent field performance elevates perceived risk and discourages uptake. Adoption is further shaped by compatibility with existing agronomic practices, extension services, credit availability, and insurance mechanisms (van Asseldonk et al. 2023). Given socioeconomic heterogeneity among farming systems, region‐specific validation and participatory approaches are necessary to align technological innovation with farmer priorities.

Methodological heterogeneity limits reproducibility and translational progress in microbiome research. Establishing standardized experimental and analytical frameworks is fundamental for agronomic application. Differences in soil sterilization, stress imposition, inoculum preparation, sequencing depth, phenotyping metrics, plant genotypes, and bioinformatic workflows reduce comparability across microbiome studies and highlight the urgent need for standardized experimental and analytical frameworks (Amos et al. 2020; De Wolfe and Wright 2023). Standardized, multi‐stress designs that reflect realistic field conditions are required to enhance translational relevance. Comprehensive metadata reporting—covering soil properties, climate variables, plant genotypes, microbial traits, sequencing pipelines, and statistical approaches—improves transparency and reproducibility (Wen, Cao, and Wei 2025). Adoption of structured frameworks such as STREAMS enhances data harmonization and integrative modeling (Moinat et al. 2023). Variation in sequencing platforms, bioinformatics workflows, taxonomic resolution, and functional annotation methods creates inconsistencies across datasets, hindering identification of generalizable patterns (Gioula and Exindari 2025). Harmonized analytical standards are essential for predictive modeling. The absence of benchmark soils, reference consortia, standardized stress assays, and harmonized phenotyping metrics limits the objective comparison and cross‐laboratory validation (Tegegne and Savidge 2025). Establishing universal benchmarks is crucial to transition microbiome engineering from exploratory research to reliable, climate‐resilient agricultural practice.

6. Integrative Research Gaps and Future Perspectives

Despite substantial advances in plant stress biology, important questions remain about how plants respond to multiple stresses occurring at the same time. Most current knowledge derives from single‐stress experiments, whereas plants in field environments experience temporally dynamic and interacting stressors. Combined stresses induce non‐additive effects on redox homeostasis, hormonal balance, and metabolic reprogramming that cannot be predicted from isolated responses (Xalxo et al. 2020; Zhang, Liu, et al. 2023; Zhang, Xu, et al. 2023; Pang et al. 2025). A predictive framework linking signaling cross‐talk to whole‐plant performance under fluctuating conditions is still lacking.

Mechanistic integration of plant signaling with microbiome function represents a major unresolved challenge. Although stress‐induced restructuring of rhizosphere communities is widely reported (Dildar et al. 2025; Zenteno‐Alegría et al. 2024), causal links between microbial functions and host physiological resilience remain insufficiently demonstrated. Taxonomic shifts are frequently described without direct quantification of nutrient fluxes, antioxidant regulation, or hormonal modulation. While functional redundancy may buffer ecosystem processes (Ramond et al. 2025; Lin et al. 2025), specialized symbiotic interactions appear vulnerable under multi‐stress exposure (Yang et al. 2025; Dubé et al. 2025). Integrating factorial stress designs with transcriptomic, metabolomic, and physiological analyses is therefore essential to establish functional causality (Wen, Cao, and Wei 2025; Gioula and Exindari 2025).

Cross‐regulatory signaling networks further complicate stress integration. Reactive oxygen species, Ca²⁺ fluxes, MAPK cascades, and phytohormones function as shared regulatory hubs coordinating concurrent stress responses (Leisner et al. 2023; Du et al. 2024; Verma et al. 2025). However, their temporal hierarchy and metabolic trade‐offs remain poorly resolved. Although priming and induced systemic resistance may enhance tolerance (Yu et al. 2022; Praveen et al. 2023), cross‐talk can also impose growth penalties (Kamran et al. 2025), necessitating quantitative, time‐resolved analyses.

Epigenetic stress memory adds another layer of complexity. DNA methylation, histone modifications, and small RNAs contribute to acclimation and transgenerational plasticity (Kinoshita and Seki 2014; Lämke and Bäurle 2017; Herman and Sultan 2011), yet their stability under repeated or combined stresses and potential interaction with microbiome‐mediated signaling remain insufficiently characterized.

Finally, translation to agronomic systems is constrained by genotype × environment × management interactions (Cooper et al. 2022; Muhammad et al. 2025) and the context dependency of microbiome‐based interventions under heterogeneous soils (Debray et al. 2022; Fadiji et al. 2025; Zhao et al. 2026). Standardized protocols, reference reagents, harmonized sequencing pipelines, and reproducible reporting systems are increasingly recognized as essential for improving cross‐study reproducibility and translational reliability in microbiome research (Amos et al. 2020; Sergaki et al. 2022). Advancing plant resilience requires integrative, physiology‐centered approaches that connect molecular signaling, cellular homeostasis, whole‐plant performance, and rhizosphere dynamics under realistic multi‐stress scenarios.

7. Conclusions

Developing climate‐resilient crops requires a transition from reductionist, single‐stress perspectives toward integrative frameworks that recognize plants as dynamic holobionts interacting continuously with their environment and associated microbiomes. Evidence synthesized in this review demonstrates that plant physiological responses, microbial functions, and environmental factors are tightly interconnected, collectively determining crop performance under multi‐stress conditions. While substantial progress has been made in understanding individual stress mechanisms and beneficial microbial functions, major gaps remain in predicting plant responses under simultaneous stresses and in translating laboratory findings to field‐scale applications. Microbiome engineering, synthetic microbial communities, and emerging precision technologies offer promising pathways to enhance resilience, but their success depends on ecological compatibility, stability in non‐sterile soils, and careful assessment of environmental impacts. Future research should prioritize multi‐factorial experiments, systems‐level modeling, and integration of omics approaches with field validation to link mechanisms with agronomic outcomes. Strengthening interdisciplinary collaborations among plant physiologists, microbiologists, agronomists, and data scientists will be essential for developing scalable solutions. Ultimately, combining physiological understandings with microbiome‐informed strategies can enable sustainable intensification of agriculture and improved crop stability, supporting global food security under accelerating climate change.

Author Contributions

Sudip Sengupta: data curation, methodology, writing original draft. Subhadwip Ghorai: data curation, methodology, writing original draft. Suvojit Bose: data curation, methodology, writing original draft. Ankur Mukhopadhyay: formal analysis, visualization. Soham Hazra: writing – review and editing. Arnab Majumdar: visualization, validation, methodology, investigation, formal analysis, writing – review and editing. Tarit Roychowdhury: data curation, investigation, methodology, visualization, writing – review and editing.

Conflicts of Interest

The authors declare no conflicts of interest.

Sengupta, S. , Ghorai S., Bose S., et al. 2026. “Integrating Plant Physiology and Microbiome Engineering for Climate‐Resilient Crops: Bridging Knowledge Gaps in Multi‐Stress Tolerance.” Physiologia Plantarum 178, no. 5: e71088. 10.1111/ppl.71088.

Data Availability Statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.