Drought-tolerant Sedum for extensive green roofs: insights into visual performance selection and integrated responses to water withholding

Abstract

Background

Selecting drought-tolerant Sedum species based on visual performance is crucial for maintaining the plants’ favorable contribution to landscape and ecosystem services in extensive green roofs (EGRs) that are frequently subjected to long-term water withholding. Current understanding of the adaptive strategies of Sedum species in response to water withholding, particularly regarding transcriptomics and metabolomics, remains limited. In this study, the visual performance and morphological, biochemical, and physiological indicators of four Sedum species under 50-day water withholding were measured, and the transcriptomic, metabolomic, and integrated multi-omics analyses were further conducted on the leaves and roots of the optimal drought-tolerant Sedum species.

Results

S. lineare Thunb. with better visual performance under 50-day water withholding was identified as the optimal drought-tolerant species. Notably, the response strategies of the four Sedum species to water withholding exhibited species-specific patterns across different indicators, and root length, root-shoot ratio, leaf water content, and photosynthetic-fluorescence indicators (excluding phosphoenolpyruvate carboxylase activity) were their key response indicators correlated with visual performance and dominant in the water-depletion stage. Transcriptomic and metabolomic analyses revealed that roots primarily upregulated the gene expression of α-galactosidase, UDP-glucose 4-epimerase, and galactinol synthase to enhance the synthesis of sucrose, trehalose, and raffinose to adapt to water decline.

Conclusion

Our findings systematically advance the current understanding of water-withholding adaptation strategies in Sedum and provide reliable theoretical support for identifying prospective breeding targets and candidate genes for drought-tolerant Sedum, thereby promoting low-maintenance and sustainable EGR implementation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12870-026-08200-x.

Introduction

Green roofs (GRs), a form of greening implemented on building rooftops, have become an integral component of urban greening and urban ecosystems [1]. Among all GR types, extensive green roofs (EGRs), typically configured with succulents or herbaceous plants and a shallow substrate layer, have broader promotion potential, as they can be implemented on building roofs that are not originally designed for GR installation at low cost [2]. However, the distinct isolation of rooftops from the ground substantially increases the costs and difficulties associated with the irrigation and management of GRs, thus resulting in the water supply for plants in most EGRs being greatly dependent on rainfall [3]. Meanwhile, the design and water storage capacity of EGR substrates are strictly limited by building code requirements to ensure the structural safety of buildings. Furthermore, the extreme microclimate environments on rooftops can accelerate the substrate evaporation and plant transpiration, leading to a significantly higher water loss rate relative to the ground level [4]. Therefore, especially in the global context of increasingly frequent and intense droughts projected for the future, plants in EGRs are often subjected to long-term water withholding, with the substrate water content consistently declining to depletion and persisting for a certain period, thereby impairing their visual performance [5]. In this context, the reduced visual performance of plants, including leaf coverage, leaf color, and leaf status, not only significantly degrades the landscape and aesthetics of EGRs that are most concerned by non-professionals but also undermines their multiple ecological service benefits [6, 7].

Sedum generally exhibits adaptive phenotypic traits such as succulent leaves and shallow root systems, coupled with a unique crassulacean acid metabolism (CAM) photosynthetic pathway, which enables these species to efficiently conserve water and utilize atmospheric CO₂ [8]. These characteristics endow Sedum species with strong drought tolerance and prevent them from causing damage to building structures, thus becoming the most commonly used plant genus in EGR implementation [9]. In recent years, researchers worldwide have focused on native Sedum species and conducted several studies on the selection of drought-tolerant species and their adaptive responses to water withholding. Koźmińska et al. demonstrated that S. spurium had better drought tolerance than S. ochroleucum, S. sediforme, and S. album based on their growth parameters during a four-week water withholding period, and noted that the content of malondialdehyde (MDA) in the leaves of the tested Sedum species did not significantly increase under these drought stress conditions [10]. Song et al. compared the landscape changes and morphological responses of six Crassulaceae species suitable for GRs during a 40-day water withholding period, and the results showed that S. lineare exhibited the lowest wilting rate of 14% at the 30th day of the experiment [11]. In contrast, they noted that the content of MDA in the leaves of S. lineare and S. sarmentosum showed an increasing trend under the 40-day drought regime. Collectively, these inconsistent findings suggest that species-specific adaptive strategies may lead to significant variations in several stress-response indicators across varying water withholding durations and different Sedum species, which can even decouple from the plants’ drought tolerance. Moreover, in other relevant studies [12, 13], the selection of drought-tolerant Sedum species also relies on either plant growth parameters or the calculation of drought tolerance based on multiple plant stress-response indicators via the membership function method. Consequently, the drought-tolerant Sedum species selected based on those criteria rather than their visual performance, which is closely linked to both the landscape and ecosystem services of EGRs, may fail to achieve desirable application outcomes in practical EGRs. Thus, selecting drought-tolerant Sedum species capable of consistently maintaining favorable visual performance under long-term water withholding can promote the low-maintenance popularization and sustainable development of EGRs across broader climatic regions. Furthermore, elucidating the adaptive strategies of Sedum species in response to water withholding, including the dominant indicators associated with stress response and visual performance, can provide a robust theoretical basis for the evaluation and selection of drought-tolerant Sedum cultivars. Importantly, transcriptomic and metabolomic analyses can systematically reveal the key genes, metabolites, and their functional pathways involved in stress responses, thereby comprehensively and deeply unraveling the molecular mechanisms and regulatory networks underlying plant stress adaptation [14]. Similar integrative approaches, such as those combining morphological, biochemical, physiological, and molecular datasets, have been successfully applied to dissect the mechanisms underlying drought tolerance in other plants [15, 16]. To date, the visual performance-driven selection of drought-tolerant Sedum species and the current understanding of the adaptive strategies of Sedum species in response to water withholding, particularly in terms of transcriptomic and metabolomic analyses, remain limited.

To address these gaps, four local Sedum species commonly used in EGRs were selected to conduct a drought experiment with 50-day water withholding in a controlled greenhouse environment. Under the 50-day water withholding, the substrate relative water content (SRWC) in the pots for each Sedum species was monitored every day, and the experimental period was accordingly divided into two distinct drought stages: water-decline stage and water-depletion stage. Meanwhile, the visual performance, morphological, biochemical, and physiological response indicators of the Sedum species were measured at 5-day intervals. The differences in these indicators across water withholding durations and species, and the correlations between visual performance indicators, stress-response indicators, and drought stages were analyzed. Further, the transcriptomic, metabolomic, and integrated multi-omics analyses were performed on the leaves and roots of the Sedum species exhibiting optimal visual performance under water withholding. Overall, this study is the first to elucidate the integrated response of Sedum species to water withholding, identify dominant stress-response and visual performance indicators, and characterize key genes and metabolites involved in functional pathways. These findings fill the critical gap in Sedum stress regulatory mechanisms, provide a vital reference for drought-tolerant cultivar breeding and improvement, and further promote the sustainable and low-maintenance implementation of EGRs.

Materials and methods

Experimental design

The four Sedum species commonly used in extensive green roofs (EGRs), including S. lineare Thunb., S. sarmentosum Bunge, S. makinoi Maxim. and S. emarginatum Migo, were selected. These species were widely cultivated in China and their seedlings were purchased from a local horticulture company (Kunshan, Jiangsu Province, China) in March 2024. The seedlings with similar growth status were selected, and their roots were removed, with part of their stems trimmed to standardize the plant height to approximately 5 cm. Four hundred small square plastic pots (bottom length: 5.5 cm; top length: 6.5 cm; height: 6 cm) were prepared, each filled with a 5 cm-thick substrate mixture composed of 40% peat soil and 60% vermiculite (v/v). The substrate mixture was lightweight, with excellent water-holding and nutrient-retention capacities, rendering it an optimal selection for EGRs [17]. Specifically, the bulk density, field water capacity, pH value, total nitrogen, total phosphorus, and organic matter contents of the substrate mixture were 157.14 kg·m^{− 3}, 48.15%, 6.27, 2398.56 mg·kg^{− 1}, 120.61 mg·kg^{− 1}, and 315.39 g·kg^{− 1}, respectively. Then, one pretreated seedling was individually transplanted into each pot. To be specific, one hundred replicates were prepared for each Sedum species (a total of 400 plant pots).

Initially, the prepared plant pots were placed in a greenhouse with an average temperature of 30 °C, an average relative humidity of 50%, an illuminance of 53,000 lx, a photosynthetically active radiation (PAR) of 508 µmol·m^− 2·s^− 1, and a day-night cycle of 12 h/12 h. During a one-month acclimation period, each plant pot was watered with 100 mL of deionized water every five days to promote plant root elongation. After that, each plant pot was watered to saturation and placed in the same greenhouse to initiate the drought experiment with 50-day water withholding. The greenhouse environment was designed to simulate the stress-associated microclimate commonly encountered in EGRs, and a 50-day water withholding period under such conditions would result in rapid substrate water decline followed by a period of complete substrate water depletion, significantly impairing plant visual performance. The photograph of the experimental platform is shown in Supplementary Materials (Figure S1).

Sampling and measurements

Plant visual performance

Three representative replicates were selected for each Sedum species to monitor the dynamic changes in plant visual performance using a digital camera (PENTAX K-50, RICOH Co., Japan) during the drought experiment (Fig. S2). The plant visual performance indicators, including leaf coverage rate, leaf color change rate, and leaf state score, were measured every five days during the drought experiment, with the detailed determination methods provided in Supplementary Materials. These three indicators correspond to the spatial coverage, color vitality, and structural integrity of Sedum species, which collectively determine the plants’ contribution to landscape and ecosystem services in EGRs.

A visual index integrating leaf coverage rate, leaf color change rate, and leaf state score was employed as the criterion for evaluating the visual performance of Sedum species. In the absence of consensus-based or data-driven quantitative weight references for the three visual indicators in existing studies, an equal-weight strategy was adopted to avoid bias arising from subjective weight assignment. Therefore, the visual index was calculated as the arithmetic mean of leaf coverage rate, leaf color change rate, and leaf state score of each Sedum species at the same measurement time point. Before the calculation, the values of leaf coverage rate, leaf color change rate, and leaf state score were normalized to the range of 0–1 based on the mean values of all the plant pots monitored at the beginning of the drought experiment. Finally, the optimal drought-tolerant Sedum species was selected based on the mean value of visual index throughout the drought experiment.

Substrate relative water content and drought stages

Sixteen replicates were selected for each Sedum species to monitor the dynamic changes in the substrate relative water content (SRWC) during the drought experiment. An electronic balance with a precision of 0.01 g was utilized to weigh plant pots every day at 8:00 am to determine the SRWC, whose calculation is shown in Eq. 1.

1

Where SRWC is the substrate relative water content (%); W_i is the weight of the plant pots measured at the i-th day during the drought experiment (g); W_dry is the dry weight of the plant pots (g); W_saturated is the saturated weight of the plant pots measured at the beginning of the drought experiment (g).

In this study, the water-decline and water-depletion stages for each Sedum species during the drought experiment were divided based on the dynamic changes in SRWC. Specifically, the day on which the average daily SRWC change rate in the plant pots dropped below 1% after the initiation of the drought experiment was defined as the boundary between the water-decline and the water-depletion stages. This boundary thus distinguishes two distinct stages of water availability for Sedum species under long-term water withholding. During the water-decline stage, plants were considered capable of absorbing water from the substrate via root systems. In contrast, they were deemed unable to acquire water from the substrate through roots during the water-depletion stage.

Plant morphological, biochemical, and physiological responses

Three biological replicates for each Sedum species were randomly selected every five days to measure the plant morphological, biochemical, and physiological response indicators. The plant morphological response indicators included plant height, root length, leaf thickness, stem width, specific leaf area (SLA), and root-shoot ratio. The plant biochemical response indicators included the content of soluble sugars, soluble proteins, proline (Pro), flavonoids, malondialdehyde (MDA), the leaf water content (LWC), the plasma membrane permeability (PMP) and the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) of the leaves. The physiological response indicators included net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), phosphoenolpyruvate carboxylase (PEPC) activity, ratio of variable fluorescence to maximum fluorescence (F_v/F_m), and photochemical quenching coefficient (qP) of the leaves. The detailed determination methods for the plant morphological, biochemical, and physiological response indicators are shown in Supplementary Materials.

Transcriptomic analysis

Four biological replicates for the leaves and roots of the optimal drought-tolerant Sedum species were sampled separately at the beginning of the drought experiment (initial stage, IS), the boundary between the water-decline and water-depletion stages (water deficit stage, WDS), and the end of the drought experiment (extreme drought stage, EDS) for transcriptomic analysis. Among them, the differences in transcriptomic profiles between WDS and IS were defined as gene expression variations during the water-decline stage and those between EDS and WDS were defined as gene expression variations during the water-depletion stage. Additionally, the core analytical workflows for transcriptomic and metabolomic data were referenced from our previous study [18].

RNA extraction, library construction, and RNA-Seq were performed by Majorbio Biotechnology Co., Ltd. (Shanghai, China). The libraries were sequenced on the Illumina NovaSeq X Plus platform (Illumina Inc., the U.S.) to generate 150 bp paired-end reads. The total number of raw reads per sample ranged from 39 to 52 million, ensuring sufficient sequencing coverage (≥ 30×) for subsequent analysis. The sequence read archive (SRA) accessions of the transcriptomic data have been deposited in the National Center for Biotechnology Information (NCBI) (BioProject Accession Number: PRJNA1207772). The clean reads were obtained using Fastp (v.0.23.4) and de novo assembled using the Trinity platform, as no high-quality reference genome is currently available for the target Sedum species. Transcripts Per Kilobase of exon model per Million mapped reads (TPM) were calculated using RSEM (v.1.3.1) as an indicator of transcription or gene expression level. The clean reads were mapped to the assembled transcriptome, with mapping rates ranging from 89.68% to 92.09% across all samples.

Principal component analysis (PCA) was employed to evaluate the variability of samples both within and among groups. Differentially expressed genes (DEGs) were screened using DESeq2 software (v.1.42.0), with the selection criteria set as false discovery rate (FDR) < 0.05 and absolute value of log2 fold change (|log2 FC|) ≥ 1. Building on these results, functional enrichment analysis based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database was conducted to pinpoint metabolic pathways significantly enriched in DEGs. The significance threshold for enriched pathways was determined by an adjusted p-value < 0.05, which was calculated using the Benjamini-Hochberg (BH) method.

Metabolomic analysis

Seven biological replicates for the leaves and roots of the optimal Sedum species were sampled separately at the IS, WDS, and EDS for metabolomic analysis. Among them, the differences in metabolomic profiles between WDS and IS were defined as metabolite variations during the water-decline stage and those between EDS and WDS were defined as metabolite variations during the water-depletion stage.

To evaluate the stability and reproducibility of the liquid chromatography-tandem mass spectrometry (LC-MS/MS) detection system, quality control (QC) samples were prepared by pooling equal volumes of supernatants from all experimental samples. The details of the metabolite extraction and LC-MS/MS analysis are shown in Supplementary Materials. The LC-MS/MS raw data for metabolome have been deposited in the OMIX, China National Center for Bioinformation (https://ngdc.cncb.ac.cn/omix, Accession No.: OMIX010839). LC-MS/MS raw data were preprocessed using Progenesis QI software (Waters Corp., the U.S.), with internal standard peaks and any known false-positive peaks in the data matrix excluded during this process. Concurrently, metabolite identification was achieved by searching the plant-specific metabolite database (MJDBPM) self-constructed by Majorbio Biotechnology Co., Ltd. (Shanghai, China). Additionally, variables corresponding to QC samples with a relative standard deviation (RSD) exceeding 30% were eliminated, and the remaining data underwent log10 transformation to generate the final data matrix for subsequent analytical procedures.

The variability of the samples within and among the groups was analyzed using PCA. Based on the orthogonal partial least squares discriminant analysis (OPLS-DA) model and Student’s t-test, differential metabolites were identified with the criteria of Variable Importance in the Projection (VIP) > 1 and FDR-adjusted p-value < 0.05, where the BH method was adopted for multiple-testing correction to reduce false positive results. The numbers and classifications of up- and down-regulated differential metabolites in leaves and roots during the water-decline and water-depletion stages were analyzed based on their metabolic pathways and chemical structures. In this study, common metabolites refer to those consistently identified as differential metabolites within the same tissue (leaves or roots) across both the water-decline and water-depletion stages.

Integrated multi-omics analysis

The four biological replicates of leaves and roots shared between transcriptomic and metabolomic analyses were used to perform integrated multi-omics analysis. Based on the DEGs and differential metabolites identified during both the water-decline and water-depletion stages, integrated KEGG functional pathways with adjusted p-values < 0.05 corrected using the BH method were considered significantly enriched. Subsequently, detailed gene-metabolite regulatory networks containing both DEGs and differential metabolites were analyzed within these significantly enriched integrated KEGG functional pathways.

Data processing and statistics

Microsoft Excel 2021, IBM SPSS Statistics 25.0, and Origin Pro 2021 were used for data processing and statistics in the present study. All the data were presented as mean ± standard deviation (SD). The differences in the visual performance and stress-response indicators of Sedum species were analyzed across the following three aspects: the same Sedum species over the drought experiment period, the four Sedum species at the same drought experiment time point, and the mean values of the four Sedum species across the drought experiment. The Shapiro-Wilk test was first performed to verify the normality of all datasets, and Levene’s test was used to assess the homogeneity of variances. For normal datasets, one-way analysis of variance (ANOVA) followed by Tukey’s Honestly Significant Difference (HSD) test (homogeneous variances) or Games-Howell test (heterogeneous variances) for post-hoc multiple comparisons was performed. For non-normal datasets, the Kruskal-Wallis test was adopted instead, with the Dunn’s test for pairwise comparisons. Specifically, for the one-way ANOVA focusing on the same Sedum species over the drought experiment period, the F-value (F_{(dfn, dfd)}) and corresponding between-group (dfn) and within-group (dfd) degrees of freedom were used to determine whether there were significant differences in its visual performance and stress-response indicators at different drought experiment time points, with the time points showing significant changes further identified and labeled. For the differences in the visual performance and stress-response indicators among the four Sedum species at the same drought experiment time point and across the drought experiment, the letter labelling method was used to indicate significant differences, where different lowercase letters represent significant differences between groups. Additionally, Spearman correlation coefficient (r) was used to analyze the correlations between stress-response indicators and visual performance indicators across the four Sedum species, as well as the dominant response indicators of Sedum species to water withholding and their differences between the water-decline and water-depletion stages. Specifically, group differences or variable correlations were considered statistically significant for all statistical tests when p-values were less than 0.05 (p < 0.05).

Results

Substrate relative water content and visual performance in Sedum species under water withholding

S. lineare had a higher SRWC compared with other Sedum species during the drought experiment (p < 0.05) (Fig. 1a). In this context, the 20th day of the drought experiment was determined as the boundary between the water-decline and water-depletion stages for S. lineare. Moreover, the boundaries between these two stages for S. sarmentosum, S. makinoi and S. emarginatum were on the 17th, 17th, 19th day of the drought experiment, respectively.

Fig. 1.

Changes and differences in substrate relative water content and visual performance of Sedum species during the drought experiment (a) Substrate relative water content (b) Leaf coverage rate (c) Leaf color change rate (d) Leaf state score (e) Visual index (In Fig. 1, each colored component corresponds to each Sedum species. In Fig. 1b-e, the colored continuous error bars represent the standard deviation of the measured indicators; F-values indicate the degree of effect of the drought experiment period on the measured indicators; colored asterisks indicate significant differences (p < 0.05) in the measured indicators between the specific drought experiment time point and the previous time point; the colored lowercase letters represent the significance of differences in the measured indicators among groups at the specific drought experiment time point; the colored bar charts show the mean values of the measured indicators during the drought experiment, with the lowercase letters indicating the significance of differences among groups; different lowercase letters indicate significant differences among groups at p < 0.05.)

Except for a slight increase in leaf coverage rate on the 5th day of the drought experiment, the leaf coverage rates and leaf state scores of the four Sedum species continued to decrease (p < 0.05) (Fig. 1b, d). Specifically, during the drought experiment, S. sarmentosum had the highest average leaf coverage rate (21.27% ± 8.71%) and S. emarginatum exhibited significantly greater leaf state scores than other species (p < 0.05). In addition, the leaf color change rate of the Sedum species showed a fluctuating upward trend as water withholding progressed (p < 0.05) (Fig. 1c). However, in comparison, the leaf color change rate of S. makinoi rose more rapidly during the first ten days of the drought experiment and remained above 90%. Overall, during the drought experiment, the visual index of S. lineare (0.64 ± 0.29) was slightly higher than that of S. sarmentosum (0.63 ± 0.26) and S. emarginatum (0.63 ± 0.21), while that of S. makinoi (0.40 ± 0.30) was markedly lower (p < 0.05) (Fig. 1e).

Morphological responses in Sedum species under water withholding

Generally, during the drought experiment, the four Sedum species shared comparable variation trends in the morphological response indicators. Specifically, most Sedum species showed no significant dynamic trends in plant height and root length (p > 0.05) (Fig. 2a–b), whereas their specific leaf area (SLA) exhibited a significantly decreasing trend (p < 0.05) (Fig. 2e). Throughout the drought experiment, the SLA of S. makinoi (104.82 ± 26.78 cm²·g^− 1) and S. emarginatum (150.44 ± 35.34 cm²·g^− 1) remained consistently lower than that of S. lineare (233.32 ± 94.36 cm²·g^− 1) and S. sarmentosum (248.00 ± 168.92 cm²·g^− 1) (p < 0.05). In contrast, the leaf thickness and stem width of Sedum species first increased, then decreased or fluctuated at a stable level after the 20th day of the drought experiment (Fig. 2c–d). Notably, S. lineare with the greatest plant height (8.31 ± 0.76 cm) and stem width (2.05 ± 0.21 mm) also exhibited a significantly higher leaf thickness (0.84 ± 0.17 mm) than S. sarmentosum (0.62 ± 0.12 mm) and S. emarginatum (0.62 ± 0.17 mm) (p < 0.05). Except for S. emarginatum, the root-shoot ratio of Sedum species gradually increased on average from approximately 0.1 to 0.3 with the progression of water withholding, though no significant intergroup differences were observed (p > 0.05) (Fig. 2f).

Fig. 2.

Changes and differences in the morphological response indicators of Sedum species during the drought experiment (a) Plant height (b) Root length (c) Leaf thickness (d) Stem width (e) Specific leaf area (f) Root-shoot ratio (In Fig. 2, each colored component corresponds to each Sedum species; the colored continuous error bars represent the standard deviation of the measured indicators; F-values indicate the degree of effect of the drought experiment period on the measured indicators; colored asterisks indicate significant differences (p < 0.05) in the measured indicators between the specific drought experiment time point and the previous time point; the colored lowercase letters represent the significance of differences in the measured indicators among groups at the specific drought experiment time point; the colored bar charts show the mean values of the measured indicators during the drought experiment, with the lowercase letters indicating the significance of differences among groups; different lowercase letters indicate significant differences among groups at p < 0.05.)

Biochemical responses in Sedum species under water withholding

Statistically, the duration of water withholding exerted a significant effect on all the biochemical response indicators of the four Sedum species (Fig. 3a–j) (p < 0.05). In contrast to the relatively gradual decrease in leaf water content (LWC) and stable increase in plasma membrane permeability (PMP) that were consistent across Sedum species, different species showed notably divergent sharp responsive patterns in the leaf contents of soluble sugar, total protein, proline (Pro), and malondialdehyde (MDA), as well as the activities of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) at specific time points during the drought experiment. Specifically, the content of soluble sugar and Pro in the leaves of S. lineare separately showed a significantly abrupt surge to over 30 mg·g^− 1 and 130 µg·g^− 1 on the 25th day of the drought experiment and had relatively high average values (soluble sugar: 15.21 ± 13.38 mg·g^− 1; Pro: 90.67 ± 59.07 µg·g^− 1) over this period (p < 0.05). Additionally, the CAT, POD, and SOD activities and MDA content in the leaves of Sedum species even surged dramatically by over 10-fold during the period from the 10th to the 25th day of the drought experiment (p < 0.05), whereas they remained relatively stable during other periods, with this trend being particularly pronounced in S. lineare and S. emarginatum. In contrast, the flavonoid content in the leaves of S. makinoi was substantially higher than that in other Sedum species, whereas its POD activity was significantly lower (p < 0.05). Notably, S. sarmentosum had the lowest levels of most osmotic adjustment substances including total protein (46.19 ± 12.28 mg·g^− 1) and Pro (37.00 ± 16.83 µg·g^− 1), antioxidant enzyme activities (CAT and SOD), and PMP (26.13% ± 18.57%) in the leaves during the drought experiment (p < 0.05).

Fig. 3.

Changes and differences in the biochemical response indicators of Sedum species during the drought experiment (a) Soluble sugar (b) Total protein (c) Proline (d) Flavonoids (e) Leaf water content (f) Plasma membrane permeability (g) Catalase activity (h) Peroxidase activity (i) Superoxide dismutase activity (j) Malondialdehyde (In Fig. 3, each colored component corresponds to each Sedum species; the colored continuous error bars represent the standard deviation of the measured indicators; F-values indicate the degree of effect of the drought experiment period on the measured indicators; colored asterisks indicate significant differences (p < 0.05) in the measured indicators between the specific drought experiment time point and the previous time point; the colored lowercase letters represent the significance of differences in the measured indicators among groups at the specific drought experiment time point; the colored bar charts show the mean values of the measured indicators during the drought experiment, with the lowercase letters indicating the significance of differences among groups; different lowercase letters indicate significant differences among groups at p < 0.05.)

Physiological responses in Sedum species under water withholding

Similar to the biochemical responses, all the physiological response indicators of the four Sedum species measured in this study were significantly affected by the duration of water withholding (p < 0.05) (Fig. 4a–f). Specifically, the net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) of almost all Sedum species decreased significantly and sharply on the 10th day of the drought experiment (p < 0.05). In particular, the Pn of all Sedum species decreased to negative values on the 20th day of the drought experiment (p < 0.05), namely the rate of respiratory carbon release by leaves exceeded the rate of carbon fixation via photosynthesis. At this time, both Tr and Gs dropped separately below 0.20 mmol·m²·s^− 1 and 10 mmol·m²·s^− 1, and stabilized thereafter, with S. lineare (Tr: 0.27 ± 0.32 mmol·m²·s^− 1; Gs: 15.74 ± 18.44 mmol·m²·s^− 1) showing a relatively superior performance compared with S. emarginatum (Tr: 0.10 ± 0.09 mmol·m²·s^− 1; Gs: 5.78 ± 3.74 mmol·m²·s^− 1) during the drought experiment (p < 0.05). Notably, unlike S. sarmentosum and S. makinoi which showed no significant responses, the phosphoenolpyruvate carboxylase (PEPC) activity of S. lineare and S. emarginatum rose significantly on the 15th day of the drought experiment, with respective increases of 5.35-fold and 4.21-fold, but exhibited a gradual downward trend thereafter (p < 0.05). On the other hand, the ratio of variable fluorescence to maximum fluorescence (F_v/F_m) and photochemical quenching coefficient (qP) of all Sedum species showed a comparable declining trend as water withholding progressed, among which the F_v/F_m of S. sarmentosum (mean: 0.61 ± 0.09) was higher than that of other species both after the 15th day and throughout the entire drought experiment (p < 0.05).

Fig. 4.

Changes and differences in the physiological response indicators of Sedum species during the drought experiment (a) Net photosynthetic rate (b) Transpiration rate (c) Stomatal conductance (d) Phosphoenolpyruvate carboxylase activity (e) Ratio of variable fluorescence to maximum fluorescence (f) Photochemical quenching coefficient (In Fig. 4, each colored component corresponds to each Sedum species; the colored continuous error bars represent the standard deviation of the measured indicators; F-values indicate the degree of effect of the drought experiment period on the measured indicators; colored asterisks indicate significant differences (p < 0.05) in the measured indicators between the specific drought experiment time point and the previous time point; the colored lowercase letters represent the significance of differences in the measured indicators among groups at the specific drought experiment time point; the colored bar charts show the mean values of the measured indicators during the drought experiment, with the lowercase letters indicating the significance of differences among groups; different lowercase letters indicate significant differences among groups at p < 0.05.)

Correlation analysis among indicators and drought stages

In contrast to the mostly non-significant correlations observed for antioxidant enzyme activities, root length, root-shoot ratio, LWC, and photosynthetic-fluorescence indicators excluding PEPC activity were all closely correlated with the visual performance indicators of Sedum species (Fig. 5). On the other hand, leaf color change rate, visual index, Pro, LWC, PMP, MDA, P_n, T_r, Gs, and F_v/F_m were the primary response indicators common to the four Sedum species in the present study. Furthermore, the responses of these indicators were more pronounced in the water-depletion stage than in the water-decline stage. In addition, leaf coverage rate, leaf state score, and qP of Sedum species exhibited a more significant decreasing trend in the water-depletion stage, whereas root length, root-shoot ratio, soluble sugar, and total protein showed a marked increase.

Fig. 5.

Overall correlations between the stress-response indicators and visual performance indicators, as well as their responses to water withholding and different drought stages (In Fig. 5, the numerical values on the colored blocks represent the Spearman correlation coefficients (r), p < 0.05)

Transcriptomic analysis of S. lineare under water withholding

The 50-day water withholding significantly affected the gene expression in the leaves and roots of S. lineare (Fig. 6a-b). For both the leaves and the roots, the number of DEGs in the water-decline stage was higher than that in the water-depletion stage (Fig. 6c). Compared with the greater number of down-regulated DEGs in S. lineare roots during the drought experiment, the leaves exhibited more significantly up-regulated DEGs during the water-decline stage.

Fig. 6.

Overall transcriptomic analysis of the leaves and roots of S. lineare during the drought experiment (a) PCA analysis of the variability of the transcriptomic profiles in S. lineare leaves within and among the different drought stages (b) PCA analysis of the variability of the transcriptomic profiles in S. lineare roots within and among the different drought stages (c) Numbers of up-regulated and down-regulated differentially expressed genes in the leaves and roots of S. lineare during the water-decline and water-depletion stages (d)-(e) KEGG pathway analysis of the leaves and roots of S. lineare during the water-decline stage (f)-(g) KEGG pathway analysis of the leaves and roots of S. lineare during the water-depletion stage (p < 0.05)

Specifically, the DEGs in S. lineare leaves were significantly enriched in several signal transduction pathways including Plant hormone signal transduction, MAPK signaling pathway, and Plant-pathogen interaction. Moreover, the gene expression in the pathways of Photosynthesis-antenna protein and Carotenoid biosynthesis was remarkably upregulated, and that in D-amino acid metabolism was downregulated instead (Fig. 6d). In contrast, during the water-depletion stage, fewer DEGs were enriched and mostly downregulated in the signal transduction pathways of S. lineare leaves, while the gene expression of some ABC transporters (ABCG5 and PDR5) remained upregulated (Fig. 6f). Notably, the gene expression of PYR/PYL, SnRK2, and ABF families in the typical ABA signaling pathway exhibited completely differential responses in S. lineare during the water-decline and water-depletion stages.

On the other hand, in S. lineare roots during the water-decline stage, the expression of genes related to Photosynthesis and Circadian rhythm was significantly upregulated (Fig. 6e). Additionally, the significantly enriched pathways of Starch and sucrose metabolism, Monoterpenoid biosynthesis, and Glycosphingolipid biosynthesis, except for Phenylpropanoid biosynthesis, were upregulated to a certain extent. In addition to maintaining a significant down-regulation of Phenylpropanoid biosynthesis, the gene expression associated with Flavonoid biosynthesis, Stilbenoid, diarylheptanoid and gingerol biosynthesis, and Pentose and glucuronate interconversions in S. lineare roots were all downregulated during the water-depletion stage (Fig. 6g).

Metabolomic analysis of S. lineare under water withholding

Overall, the variability in the metabolomic profiles and the number of differential metabolites in S. lineare roots during the drought experiment were markedly higher than those in the leaves (Fig. 7a-c). However, both in the leaves and roots, there were more up-regulated metabolites during the water-decline stage and the proportion of down-regulated metabolites dominated during the water-depletion stage. Notably, approximately two-thirds of the common metabolites in leaves across the two drought stages showed consistent regulatory trends, whereas the opposite was observed in roots, which had a significantly large number of common metabolites.

Fig. 7.

Overall metabolomic analysis of the leaves and roots of S. lineare during the drought experiment (a) PCA analysis of the variability of the metabolomic profiles in S. lineare leaves within and among the different drought stages (b) PCA analysis of the variability of the metabolomic profiles in S. lineare roots within and among the different drought stages (c) Numbers of up-regulated and down-regulated differential metabolites in the leaves and roots of S. lineare during the water-decline stage, the water-depletion stage, and between these two stages (d) Classification of up-regulated and down-regulated differential metabolites in the leaves and roots of S. lineare during the water-decline and water-depletion stages (p < 0.05)

For the classification of differential metabolites in S. lineare leaves during the water-decline stage, lipids, flavonoids, and carbohydrates and derivatives were dominant in up-regulation (Fig. 7d). However, during the water-depletion stage, amino acids and derivatives in S. lineare leaves were significantly upregulated, whereas lipids, terpenoids, and flavonoids showed marked down-regulation. On the other hand, the metabolites that were significantly upregulated in S. lineare roots during the water-decline stage, including flavonoids, terpenoids, amino acids and derivatives, and lipids, were also substantially downregulated during the water-depletion stage. In contrast, coumarins, phenolic acids, and their derivatives in S. lineare roots during the water-depletion stage maintained a relatively higher ratio of up-regulation to down-regulation.

Integrated multi-omics analysis of S. lineare under water withholding

Based on the transcriptomic and metabolomic profiles, ABC transporters was the only common pathway significantly enriched in both gene expression and metabolite changes in the leaves and roots of S. lineare during the water-decline and water-depletion stages (Fig. 8). For the leaves, the abundances of sucrose and D-glucose, as well as most DEGs belonging to ABC transporter superfamily, were upregulated during the water-decline stage. In addition, guanosine and deoxyguanosine in S. lineare leaves during the water-depletion stage exhibited differential changes, with the down-regulated gene expression associated with ABC transporters.

Fig. 8.

Significantly enriched integrated KEGG pathways of the leaves and roots of S. lineare and their detailed gene-metabolite regulatory networks during the water-decline and water-depletion stages (In Fig. 8, the horizontal dashed line indicates the p-value threshold of 0.05)

By comparison, in S. lineare roots during the water-decline stage, the abundances of nucleoside metabolites such as adenosine, guanosine, and deoxyguanosine, as well as carbohydrates including raffinose, trehalose, and sucrose, were simultaneously enhanced, along with the gene expression of some ABC transporter members. In this case, except for these carbohydrates, S. lineare also strengthened the synthesis of dextran, inulin, stachyose, D-galactose, and galactosyl-glycerol in the roots by upregulating the expression of key genes (e.g., EC 3.2.1.22, β-fructofuranosidase; EC 5.1.3.2, UDP-glucose 4-epimerase; EC 2.4.1.123, galactinol synthase) involved in the pathways of Starch and sucrose metabolism and Galactose metabolism. Meanwhile, the abundances of glutathione disulfide and L-γ-glutamylcysteine were increased by upregulating the expression of genes such as EC 1.8.5.1, glutathione dehydrogenase (ascorbate) and EC 1.11.1.9, glutathione peroxidase enriched in the pathway of Glutathione metabolism. On the contrary, during the water-depletion stage, S. lineare roots significantly downregulated the gene expression and metabolite synthesis enriched in the pathway of Phenylpropanoid biosynthesis and lowered the abundances of several important amino acids, carbohydrates, nucleosides, and choline, as well as the expression of ABC transporter genes other than ABCB1.

Discussions

In the present study, among the four Sedum species, S. lineare exhibited the highest average visual index under 50-day water withholding (average temperature 30 °C, average air humidity 50%), thus being identified as the optimal drought-tolerant Sedum species for extensive green roofs (EGRs). In general, long-term water withholding in EGRs impairs plant physiological and metabolic activities by reducing water availability, thereby compromising growth status and visual performance [19]. Against this backdrop, species-specific response strategies in morphology, biochemistry, and physiology to variable water availability exert differential impacts on plant adaptability under long-term water withholding [20, 21]. Specifically, S. lineare had superior above-ground morphological traits (plant height and stem width), and stronger osmotic adjustment, antioxidant, and stomatal regulation capacities compared with the other Sedum species. Similarly, S. emarginatum shared mostly consistent biochemical and physiological response patterns with S. lineare but maintained the highest net photosynthetic rate (Pn) at minimal stomatal conductance (Gs) and transpiration rate (Tr) under water withholding. In contrast, S. sarmentosum showed stable low-level responses in osmotic adjustment and antioxidant indicators, while maintaining favorable plasma membrane permeability (PMP) and ratio of variable fluorescence to maximum fluorescence (F_v/F_m) during the water-depletion stage. Interestingly, S. makinoi exhibited almost undetectable peroxidase (POD) activity but uniquely synthesized high levels of flavonoids to alleviate oxidative damage [22]. Consistent with previous findings, Song et al. reported higher POD and superoxide dismutase (SOD) activities in S. lineare [11], while Zhang et al. confirmed species-specific variations in physiological and biochemical parameters of green roof plants under drought stress [13]. Admittedly, these stress-response indicators correlate with plant drought tolerance to a certain extent and are widely incorporated into drought tolerance evaluation frameworks for Sedum and other species [13, 23]. However, the stage-specific variation characteristics of several indicators observed among different Sedum species suggest that even congeneric species may exhibit considerable differences in the response sensitivity and quantitative values of these indicators to water withholding duration [24]. Furthermore, although S. lineare, S. sarmentosum, and S. emarginatum adopted distinct response strategies to water withholding, no significant differences were observed in their average visual index under 50-day water withholding. This might be attributed to the preliminary verification of good drought tolerance in all the four species in previous studies [11], but it also highlights that selecting drought-tolerant species solely based on non-screened stress-response indicators may result in unsatisfactory field performance. Therefore, the common water-withholding response indicators and their stage-specific differences identified in this study provide scientific support for elucidating the general adaptive mechanisms of Sedum species and optimizing their drought tolerance evaluation framework. Most importantly, linking cross-species data on morphological, biochemical, and physiological response indicators to plant visual performance offers reliable biological markers and targeted approaches for screening, breeding, and managing drought-tolerant Sedum species [25]. Additionally, the differences in specific visual performance indicators among S. lineare, S. sarmentosum, and S. emarginatum enable flexible species selection for diverse EGR scenarios, such as preferences for high plant coverage or visually attractive leaf coloration [26]. Nevertheless, for the evaluation of EGR plants, the selection, determination methods, and weight assignment of visual performance indicators require further development of a universal and quantitative methodology based on plants’ contribution to the landscape and ecological services. For instance, integrating a three-dimensional plant phenotyping platform for objective real-time visual performance measurements with analytical hierarchy process (AHP) and cost-benefit analysis can optimize this methodology [6, 27]. In addition, although the greenhouse experimental conditions and water withholding duration in this study have attempted to simulate the in-situ stress environment of EGRs to the greatest extent, discrepancies still exist between controlled settings and complex field conditions (e.g., variable ambient temperature, uneven substrate moisture distribution in the field). These discrepancies, coupled with the significant impacts of tested local plant species and growing substrates on their stress adaptation in natural scenarios, highlight the necessity of more extensive and systematic EGR plant selection studies at field sites across broader climatic regions [28].

Further, this study presents the first transcriptomic and metabolomic analysis of leaves and roots of S. lineare under water withholding, significantly advancing the understanding of molecular mechanisms and adaptive strategies underlying stress responses in Sedum species (Fig. 9). Compared with the selected biochemical response indicators, the transcriptomic and metabolomic profiles of S. lineare more comprehensively characterize variations in gene expression and metabolite accumulation within core functional pathways involved in its adaptation to water withholding [29]. Overall, S. lineare adopts an active stress-adaptive strategy of accelerating resource allocation and enhancing metabolic activity during the water-decline stage and switches to a conservative survival strategy of reducing non-essential metabolic energy consumption to alleviate cell damage during the water-depletion stage. Specifically, during the water-decline stage, synergistic regulation by plant hormones, MAPK, and plant-pathogen interactions upregulated genes for photosynthetic antenna proteins and carotenoid biosynthesis in S. lineare leaves, as well as synthesis of lipids, flavonoids, and carbohydrates including sucrose and glucose. With decreasing substrate water availability, altered stomatal guard cell osmotic pressure and activated crassulacean acid metabolism (CAM) photosynthesis reduced Gs and photosynthetic carbon fixation, inducing Rubisco oxygenation, photorespiration, and reactive oxygen species (ROS) overproduction [30]. In response, upregulated antenna proteins and carotenoids optimize photosynthetic efficiency by slowing energy transfer and mitigating ROS, which in turn sustains the synthesis of sucrose and glucose for osmotic adjustment and energy supply [31]. Moreover, carotenoids not only reduce ROS generation via non-photochemical quenching mechanisms but also, together with the elevated flavonoids, scavenge excess intracellular ROS, thereby preserving plasma membrane integrity and the normal function of photosystems and other organelles [32]. Furthermore, enhanced lipid synthesis preserved membrane fluidity and alleviated dehydration, while ABC transporters ensured intercellular substance transport [33, 34]. Notably, the ABA signaling negative regulator PP2C was sustainably upregulated under water withholding. From water-decline to water-depletion stages, ABA signaling receptor PYR/PYL shifted from up-regulation to down-regulation, whereas SnRK2 and ABF were gradually upregulated. The observation that ABA-mediated responses dominated only in the water-depletion stage, coupled with the marked up-regulation of MAPK and WRKY genes in the water-decline stage, indicates that the physiological and biochemical adaptive strategies of S. lineare under water withholding are governed by a complex regulatory network with signal crosstalk [35]. This stage-specific signal crosstalk among ABA, MAPK, and WRKY pathways is likely to modulate the induction and maintenance of CAM photosynthesis, coordinating the trade-off between water conservation and carbon assimilation under long-term water withholding [36]. Although the transcriptomic and metabolomic profiles of S. lineare leaves exhibited distinct stage-specific differences, the division of water withholding into only two discrete stages (water-decline and water-depletion) in this study has to some extent limited the precise characterization of the dynamic transition nodes underlying its drought tolerance mechanisms. Moreover, the activation of CAM photosynthesis in Sedum species under water withholding was verified via phosphoenolpyruvate carboxylase (PEPC) activity assays, yet nocturnal CO₂ assimilation rate and vacuolar malic acid accumulation were not measured, which limits the direct link between molecular regulatory pathways and the full physiological spectrum of CAM. Future studies should combine omics analyses under refined water availability gradients with measurements of malic acid dynamics and nocturnal CO₂ fixation rates to further dissect the specific interaction nodes among MAPK, WRKY and ABA pathways, as well as their regulatory relationships with key CAM processes, providing a precise basis for elucidating plant stress adaptation mechanisms. During the water-depletion stage, carbon assimilation in S. lineare leaves almost ceased, and non-essential metabolite synthesis (lipids, terpenoids, flavonoids) was significantly downregulated, with only amino acid synthesis upregulated to maintain basic survival metabolism. Yang et al. reported that the desert moss Syntrichia caninervis accumulates amino acids for dehydration protection and post-rehydration recovery, which function as protective agents and nitrogen-carbon reservoirs [37]. Accordingly, maintaining a high amino acid synthesis efficiency may also be a conserved metabolic mechanism for S. lineare to cope with water depletion and dehydration, underpinning its ability to maintain cellular stability under long-term water withholding and potentially achieve rapid recovery after rehydration. Importantly, it is of great significance to take this trait as an improvement target for ensuring the survival and maintenance of favorable visual performance of plants in EGRs that are frequently exposed to long-term water withholding and rehydration.

Fig. 9.

Stage-specific response strategies of S. lineare to water withholding

On the other hand, as the primary tissue for perceiving and responding to water withholding, roots exhibit more active and stage-specific adaptive strategies than leaves, which complements the leaf-centered metabolic and signaling regulatory networks described above. In detail, during the water-decline stage, limited resources were allocated more to roots for elongation and development to strengthen the water-nutrient adsorption and transport. Meanwhile, the synthesis of amino acids and glycosphingolipids was upregulated to enhance cellular osmotic adjustment capacity and membrane stability. Specifically, genes and associated metabolites involved in glutathione synthesis (composed of L-glutamic acid, L-cysteine, and glycine) were upregulated, highlighting glutathione’s dominant role in the antioxidant defense system of S. lineare roots by scavenging excessive intracellular ROS [38]. Moreover, the upregulated expression of genes involved in circadian rhythms and photosynthesis pathways suggests potential photosynthetic or carbon assimilation-related activity in the shallow root systems of S. lineare, which may serve as a unique supplement to leaf CAM photosynthesis under water withholding. Suetsugu et al. noted that the roots of some Orchidaceae species with CAM photosynthesis possess characteristics including high concentration of photosynthetic pigments, high rate of photosynthetic electron transport, high capacity for photosynthetic gas exchange, and nocturnal CO₂ fixation [39]. Interestingly, as a CAM plant, S. lineare may share similar specific carbon assimilation functions in its roots with the Orchidaceae species, which will expand our understanding of the key mechanisms by which CAM photosynthesis endows Sedum plants with excellent drought resistance. However, direct quantitative evidence for the carbon fixation efficiency and its underlying regulatory mechanisms in S. lineare roots is still lacking to date, and these aspects need to be further elucidated through carbon isotope analysis and phenotypic anatomical studies. Additionally, several key genes and carbohydrates involved in the pathways of starch and sucrose metabolism and galactose metabolism were synchronously upregulated to improve the synthesis and transport efficiency of many osmotic regulatory substances and antioxidants associated with drought defense in plants. Notably, the significantly increased oligosaccharides such as sucrose, trehalose, and raffinose observed in the roots of S. lineare during the water-decline stage are key metabolites that constitute the core mechanism underlying drought tolerance in plants [40]. Liang et al. found that Codonopsis pilosula significantly enhanced the accumulation of sucrose, raffinose, and trehalose in the roots and rhizosphere in response to drought, which induced the assembly of rhizosphere beneficial microbial communities [41]. Moreover, they verified that exogenous application of trehalose and raffinose in the rhizosphere could enhance the drought tolerance of Codonopsis pilosula. Therefore, the increased accumulation of sucrose, raffinose, and trehalose in the roots of S. lineare could enhance its osmotic adjustment capacity to strengthen the water uptake efficiency and drought tolerance. However, the interplays between root oligosaccharide accumulation and rhizosphere microbial community assembly in S. lineare, as well as their synergistic contributions to drought tolerance, require further clarification through combined rhizosphere microbiome and metabolome analyses. Furthermore, the identified key rate-limiting genes (EC 2.4.1.82, EC 2.4.1.15) involved in raffinose and trehalose synthesis that were not completely upregulated in this study can serve as target genes for overexpression via molecular biology techniques to further enhance the drought tolerance of S. lineare [42]. Besides, certain upregulated flavonoids and terpenoids may also accumulate in the rhizosphere to act as signaling molecules, which defend against soil-borne microbial pathogens, to alleviate the secondary biotic stress and functional damage to plant roots under water withholding [43]. Conversely, during the water-depletion stage, due to the inability to acquire available resources from a completely dry substrate, the roots of S. lineare may adopt a strategy of prioritizing resource allocation to leaves with greater photosynthetic capacity and succulent characteristics to prepare for subsequent rehydration. Under such circumstances, all the gene expression in their enriched KEGG functional pathways and the synthesis of metabolites in each classification were downregulated, especially flavonoids, terpenoids, lipids, and amino acids. In contrast, with the significantly downregulated upstream core pathway of phenylalanine biosynthesis, the limited resources in the roots still relatively maintain the synthesis of coumarins, phenolic acids, and their derivatives to inhibit severe membrane lipid peroxidation caused by water depletion [44].

In conclusion, this study conducted a drought experiment with 50-day water withholding under simulated EGRs conditions (30 °C average temperature, 50% average air humidity) and selected S. lineare as the optimal drought-tolerant Sedum species for EGRs application based on a comprehensive visual index integrating leaf coverage, leaf color change, and leaf state. Additionally, the adaptive strategies of the four Sedum species in terms of morphological, biochemical, and physiological responses to water withholding were systematically elucidated, and their common key visual performance-associated and stage-specific response indicators were identified. Further transcriptomic, metabolomic, and integrated multi-omics analyses revealed that S. lineare adopts stage-specific adaptive strategies under water withholding: an active defense strategy centered on enhancing metabolic activity (e.g., oligosaccharide, carotenoid, and glutathione synthesis) and signal pathway crosstalk (ABA-MAPK-WRKY) during the water-decline stage, and a conservative survival strategy focusing on maintaining basic metabolism (e.g., leaf amino acid and root coumarin synthesis) during the water-depletion stage. Crucially, the key signaling mechanisms and gene-metabolite regulatory pathways identified in this study also provide direct molecular targets for future drought-tolerant Sedum breeding and improvement. Overall, these findings advance the visual performance-driven selection framework for drought-tolerant Sedum species in EGRs and elucidate the integrated morphological, biochemical, physiological, and molecular responses of Sedum to water withholding, providing both theoretical insights and practical guidance for selection and sustainable management of Sedum in EGRs.

Authors’ contributions

CX designed the study and wrote the original manuscript. WP and QZ conducted the experiment and helped analyze data. DF supervised the study and edited the manuscript. All authors read and approved the final manuscript.

Funding

Not applicable.

Data availability

The sequence read archive (SRA) accessions of the transcriptomic data have been deposited in the National Center for Biotechnology Information (NCBI) (BioProject Accession Number: PRJNA1207772). The LC-MS/MS raw data for metabolome have been deposited in the OMIX, China National Center for Bioinformation (https://ngdc.cncb.ac.cn/omix, Accession No.: OMIX010839). The other datasets generated during and analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.