Nano-silica optimizes C: N: P: K stoichiometry and nutrient accumulation in Dendrocalamus brandisii seedlings

Abstract

Bamboo plays an important role in forest ecosystem conservation and carbon sequestration, but the effects of foliar nano-silica on nutrient accumulation and stoichiometric regulation in bamboo remain unclear. In this study, six foliar SiO₂ nanoparticle (SiO₂ NP) concentrations, 0, 100, 200, 300, 400, and 500 mg·L⁻¹, were applied to Dendrocalamus brandisii seedlings. Leaf SPAD values, SiO₂ content, C, N, P, and K concentrations, and related stoichiometric ratios were determined. Results showed that the 300 mg·L⁻¹ treatment (T3) produced the most favorable overall response, particularly enhancing leaf SPAD values, SiO₂, P, and K accumulation and maintaining relatively high N content, while altering multiple stoichiometric ratios among SiO₂, C, N, P, and K. Correlation and PCA analyses indicated that SPAD was closely associated with SiO₂, N, and P contents. In contrast, the highest concentration, 500 mg·L⁻¹, reduced SPAD values and nutrient accumulation, suggesting that excessive nano-silica application may negatively affect seedling performance. These findings indicate that moderate SiO₂ NP application may improve leaf nutrient status and C: N: P: K stoichiometric coordination in D. brandisii seedlings, providing a potential supplementary approach for improving bamboo seedling quality and supporting conservation-oriented bamboo plantation management.

Background

Bamboo is widely distributed across tropical and subtropical regions worldwide, covering approximately 35 million ha of land across Africa, Asia, and the Americas according to the Global Forest Resources Assessment 2020 [1]. Among these, China is one of the richest countries in bamboo resources, with a bamboo forest area of approximately 7.56 million ha [2]. Owing to its extremely rapid growth and strong regenerative capacity, bamboo constitutes a key non-wood plant resource critical to both forest ecosystems and agroforestry-based economies. It functions not only as a significant biological carbon sink for climate-change mitigation and ecological restoration [3], but also as a strategic non-wood forest product that supplies raw materials for sustainable construction, biomaterials, and the textile industry. Hence, improving bamboo productivity is of paramount ecological and economic importance. Enhancing bamboo forest productivity depends not only on the capacity for carbon (C) accumulation but also on the efficient uptake and balanced stoichiometry of key nutrients, such as nitrogen (N), phosphorus (P), and potassium (K) [4]. Insights from ecological stoichiometry further indicate that elemental ratios such as C: N and N: P provide robust indicators of plant nutrient-use efficiency and plant responses to environmental stress [5]. More broadly, plant responses to nutrient additions depend on a range of interacting factors, including soil properties, microbial processes, fertilizer type, and elemental stoichiometric balance. This highlights the need to evaluate nutrient regulation from an integrated stoichiometric perspective. For example, the co-application of organic amendments and inorganic phosphorus has been reported to increase maize growth, soil organic carbon, and phosphorus availability in calcareous soil [6]. In addition, variation in soil carbon and phosphorus fractions is closely associated with microbial biomass, indicating that microbial processes play an important role in nutrient transformation and availability [7]. More recently, soil C/P stoichiometry has been shown to mediate microbially driven phosphorus mobilization, providing new insights into soil phosphorus management and nutrient cycling [8]. These findings suggest that plant responses to nutrient additions are closely related to nutrient availability, microbial regulation, and elemental stoichiometric balance.

Silicon (Si), although not classified as an essential plant nutrient, has been increasingly recognized as a beneficial element that reinforces cell walls, enhances stress tolerance, and optimizes nutrient uptake [9, 10]. It enhances photosynthetic efficiency, improves the structural stability of cell walls and membranes, regulates ion homeostasis, and alleviates multiple abiotic stresses [11, 12]. Si is often deposited in the form of rigid amorphous silica gel in cell walls and intercellular spaces, forming dense silica deposits; when it accumulates beneath the leaf epidermis and cuticle, it can form a typical “silicified layer” that thickens the epidermis and associated tissues and partially covers or surrounds stomatal regions, thereby reducing water loss and helping to regulate stomatal opening and closing under stress conditions [13]. Previous studies have shown that an adequate silicon supply in bamboo species can improve photosynthetic performance, enhance structural biomass accumulation, and improve environmental adaptability [14, 15]. However, research on silicon nutrition in bamboo has mainly focused on soil-applied silicon, with relatively little attention paid to foliar silicon application and its concentration-dependent effects. Silicon dioxide nanoparticles (SiO₂ NPs), also referred to as nano-silica, are nanoscale silicon materials characterized by small particle size and large specific surface area [16, 17]. In contrast to traditional silicon fertilizers, nano-silicon more efficiently penetrates plant tissues via leaf stomata and the cuticular layer, markedly increasing silicon bioavailability and elevating SiO₂ accumulation in plant tissues, while also strengthening stress tolerance by improving resistance to pathogens and pests, drought, and heavy metal stress [18]. It is increasingly recognized as an important beneficial silicon source for plants, offering high bioavailability and strong reactivity even at relatively low application rates [19]. However, the nutritional regulatory role of nano-silica in bamboo and its effects on C, N, P, K, and stoichiometric ratios remain unexplored.

Photosynthesis constitutes the foundational process for plant growth and development, critically influencing biomass accumulation, carbon sequestration, and the capacity to withstand environmental stresses [20]. Among available indicators, the Soil Plant Analysis Development (SPAD) reading is a widely accepted metric of leaf photosynthetic capacity, commonly used as a proxy for chlorophyll content and overall photosynthetic efficiency [21]. However, SPAD provides an indirect indicator of leaf chlorophyll status rather than a direct measurement of photosynthetic carbon assimilation; therefore, SPAD values should be interpreted together with nutrient and stoichiometric traits for a more comprehensive evaluation. In bamboo species, photosynthetic efficiency is a primary determinant of growth rate and biomass production, making the enhancement of photosynthetic capacity critical for improving stand productivity [22]. To this end, it is important to recognize that photosynthetic capacity is a function not only tightly linked to chlorophyll content but is also jointly regulated by nutrient supply, soil conditions, and climatic factors [23]. Studies indicate that interactions among C, N, P, and K strongly influence photosynthetic efficiency and growth [24], a balanced supply of N, P, and K further promotes the synthesis and turnover of photosynthetic pigments and enhances plant light-use efficiency [25]. In recent years, SiO₂ NPs have attracted increasing attention due to their capacity to enhance photosynthetic traits, nutrient uptake, and ionic homeostasis through foliar or soil application. Studies have demonstrated that nano-silicon application can significantly increase SPAD values, improve photosynthetic efficiency, and promote the uptake and redistribution of mineral nutrients, especially K and N, under both optimal and stress conditions [26–28]. Mechanistically, foliar-applied SiO₂ NPs may influence leaf nutrient accumulation through several pathways. Specifically, their small particle size and large specific surface area may facilitate contact with the leaf surface and promote entry via stomatal or cuticular pathways. Subsequently, absorbed silicon may contribute to silica deposition within epidermal tissues and cell walls, thereby altering structural investment and nutrient allocation. This, in turn, affects the uptake and transport of N, P, and K, thus shifting C: N:P: K stoichiometric patterns. However, these mechanisms remain insufficiently verified in bamboo, particularly under foliar nano-silica application. Moreover, nano-silicon has been shown to alleviate abiotic stresses by stabilizing photosynthetic apparatus, enhancing nitrogen metabolism and maintaining nutrient balance within plant tissues [29]. These findings suggest that nano-silicon not only improves plant physiological performance but also optimizes whole-plant nutritional architecture through synergistic interactions with essential elements [30]. While the benefits of nano-silicon in agriculture are increasingly recognized, its impact on bamboo remains unclear. A critical question persists: whether and how foliar application of nano-silicon alters the integrated accumulation and stoichiometric patterns of C, N, P, and K in bamboo. Resolving this knowledge gap is essential not only for advancing bamboo nutrition theory but also for formulating efficient nutrient management strategies, as highlighted by previous work [31]. This clearly defines a vital direction for future research in sustainable bamboo cultivation.

Dendrocalamus brandisii represents an important sympodial bamboo species widely cultivated in Southeast Asia, South Asia, and southwestern China. Due to its high productivity, edible shoots, and economic importance, improving seedling quality and nutrient-use efficiency is important for the effective establishment and long-term management of bamboo plantations [32, 33]. However, the effects of foliar SiO₂ NP application on leaf nutrient accumulation and C: N: P: K stoichiometric patterns in D. brandisii seedlings remain poorly understood. Informed by previous research on bamboo productivity, silicon-mediated plant responses, and ecological stoichiometry, we hypothesized that foliar application of SiO₂ NPs would affect leaf photosynthetic status and nutrient stoichiometric patterns in a concentration-dependent manner. Specifically, we predicted that moderate SiO₂ NP concentrations would promote leaf SiO₂ accumulation, SPAD values, and C, N, P, and K contents, whereas excessive concentrations would weaken these beneficial effects. To test these hypotheses, the present study applied a range of SiO₂ NP concentrations to assess their effects on the nutrient elements in D. brandisii by determining leaf SPAD values, SiO₂ content, and the concentrations of C, N, P, and K, followed by calculating relevant stoichiometric ratios. The results offer a potential supplementary approach for improving bamboo seedling quality and supporting conservation-oriented bamboo plantation management.

Materials and methods

Sample collection and preparation

The field experiment was conducted at a D. brandisii seedling nursery in Yixiang Town, Simao District, Pu’er City, Yunnan Province, China (101°03′E, 22°44′N). This study did not involve wild field sampling. Details of the local climate during the experiment are provided in Table 1, and the climate data were obtained from World Weather Online. The plant materials used in this study were one-year-old potted cutting seedlings of D. brandisii propagated from two-year-old mother bamboo plants. Before treatment, the seedlings showed relatively uniform growth, with an average height of 90.05 ± 7.67 cm (mean ± SD, n = 60), and each seedling had approximately 7–8 fully expanded leaves per branch. All seedlings were grown in plastic pots with a diameter of 12 cm and a height of 11 cm, using local Pu’er red soil as the growth substrate. Healthy seedlings with uniform growth and free from pests and diseases were selected as experimental materials. A total of 180 potted seedlings were used in the experiment. Six treatments were established, including one control treatment, CK, sprayed with distilled water, and five SiO₂ NP treatments: 100 mg·L⁻¹, T1; 200 mg·L⁻¹, T2; 300 mg·L⁻¹, T3; 400 mg·L⁻¹, T4; and 500 mg·L⁻¹, T5. For each treatment, a total of 30 seedlings were randomly divided into three independent sampling groups, corresponding to the 5th, 10th, and 15th days after the final spray, with 10 seedlings assigned to each sampling date. Each seedling was sampled only once, and seedlings sampled at one time point were not reused at subsequent sampling dates, thereby ensuring independence among samples collected at different dates. All seedlings were maintained under consistent nursery management conditions throughout the experiment. The SiO₂ NPs used in this study had an average particle size of approximately 20 nm as specified by the manufacturer (Shanghai Macklin Biochemical Technology Co., Ltd). All SiO₂ NP suspensions were freshly prepared with distilled water immediately before application and sonicated for 15 min to reduce aggregation [34], yielding a uniform colloidal suspension. Beginning after 17:00 on 27 March 2025, foliar applications of the nano-silica suspensions were carried out for CK and all treatment groups. The suspensions were sprayed evenly onto both the upper and lower leaf surfaces until the leaves were fully moistened but not dripping. Spraying was performed once every 2 d, for a total of three applications. On the 5th, 10th, and 15th days after the final spray, the second pair of fully expanded mature leaves was collected from each selected seedling, placed in 50 mL centrifuge tubes, and immediately stored in liquid nitrogen.

Table 1.

The local climate data during the experiment

Average high temperature (oC)	Average low temperature (oC)	Average temperature (oC)	Precipitation (mm)	Average humidity (%)	Average sunshine hours ( h)	Average sunny days ( d )	Average cloud amount ( % )	Average ultraviolet index
30	15	22	52.2	50	269.7	23	22	4

Climate data were obtained from World Weather Online

Determination of silicon content

All samples were oven-dried at 60 ℃ for 24 h, ground with a pulverizer (LG-04), and passed through a 40-mesh vibrating screen; the fraction retained on a 60-mesh sieve was used for ash and silicon determinations. Ash content was measured according to the Chinese national standard GB/T 2677.3–93, as described by [35]. Briefly, samples were loaded into porcelain crucibles, pre-carbonized on an electric hot plate, and then ashed in a muffle furnace at 575 ± 25 °C for 2 h before weighing. For silicon analysis, and following GB/T 7978, 5 mL of 6 mol·L⁻¹ HCl was added to the ash, and the suspension was evaporated on a steam bath; this step was repeated three times, after which the residue was washed with distilled water, filtered, and re-ashed in the muffle furnace at 575 ± 25 ℃ for 2 h, and the final mass was used for silicon quantification. All measurements were performed in triplicate.

Determination of SPAD content

SPAD values were measured between 9:00 and 10:00 a.m. using a portable chlorophyll meter (Yaxin-1260, China). For each selected seedling, fully expanded mature leaves were measured while avoiding the main vein and direct sunlight. Each leaf was measured three times, and the mean value was used for analysis [36].

Determination of C, N, P, and K contents

In this study, total C in bamboo leaves was determined using the potassium dichromate oxidation method combined with dilution and heating [37]. Total N was measured using the Nessler colorimetric method [38]. Total P was determined by the molybdenum–antimony anti colorimetric method, and total K was quantified using flame atomic absorption spectrophotometry [39]. All procedures were conducted in strict accordance with standard protocols, and the instruments were calibrated prior to analysis to ensure data accuracy and reliability.

Statistical analysis

Data were analyzed using SPSS 27.0. Before applying parametric tests, the normality of residuals and homogeneity of variances were tested using the Shapiro–Wilk test and Levene’s test, respectively. Because seedlings sampled on the 5th, 10th, and 15th days after the final spray were independent and were not repeatedly sampled, two-way analysis of variance (ANOVA) was used to test the effects of SiO₂ NP concentration, treatment time, and their interaction on SPAD values, SiO₂ content, C, N, P, and K concentrations, and stoichiometric ratios. When significant effects were detected, means were separated using Duncan’s multiple range test at p < 0.05. Pearson correlation analysis was conducted to evaluate associations among SPAD values, SiO₂ content, nutrient contents, and stoichiometric traits.

The plasticity index (P) was calculated as P = (Xmax − Xmin)/Xmax, where Xmax and Xmin denote the maximum and minimum values of each parameter, respectively.

Results

SiO₂ in D. brandisii leaves under different treatments

SiO₂ NP concentration, treatment time, and their interaction significantly affected leaf SiO₂ content in D. brandisii seedlings (Table 2). Across all treatments and sampling dates, leaf SiO₂ content ranged from 2.32% to 3.59% (Fig. 1). Compared with CK, foliar application of SiO₂ NPs generally increased leaf SiO₂ accumulation, but the response was clearly concentration-dependent. The T3 treatment produced the most stable and pronounced increase, showing the highest or among the highest SiO₂ contents across the three sampling dates. In contrast, although T5 increased SiO₂ content relative to CK, its effect was weaker than that of the medium-concentration treatments, especially at later sampling stages. Leaf SiO₂ content under T4 and T5 tended to decline after day 10, suggesting that excessive SiO₂ NP supply did not further promote silicon accumulation. Overall, these results indicate that moderate SiO₂ NP application, particularly T3, was more effective than high-concentration application in promoting SiO₂ accumulation in D. brandisii leaves.

Table 2.

Effects of SiO₂ nanoparticle concentration, treatment time, and their interaction on leaf SiO₂ content, SPAD value, and C, N, P, and K concentrations in D. brandisii seedlings

Indicator	Factor	F	p
SiO₂	Time	29.006	0.001
	Concentration	35.671	0.001
	Time × Concentration	3.601	0.002
SPAD	Time	0.061	0.941
	Concentration	111.900	0.001
	Time × Concentration	9.907	0.001
C	Time	16.338	0.001
	Concentration	65.373	0.001
	Time × Concentration	21.357	0.001
N	Time	7.545	0.002
	Concentration	18.754	0.001
	Time × Concentration	0.936	0.513
P	Time	7.506	0.002
	Concentration	44.409	0.001
	Time × Concentration	5.662	0.001
K	Time	70.237	0.001
	Concentration	10.361	0.001
	Time × Concentration	2.431	0.025

F-values and p-values were obtained from two-way ANOVA. The sources of variation included SiO₂ NP concentration, treatment time, and their interaction. p > 0.05 indicates no significant effect, p < 0.05 indicates a significant effect, and p < 0.01 indicates a highly significant effect. SiO₂ NPs, silicon dioxide nanoparticles

Fig. 1.

SiO₂ content in D. brandisii leaves under different treatments. Data are expressed as mean ± SD. Different uppercase letters above bars indicate significant differences among treatments within the same sampling time according to Duncan’s multiple range test at p < 0.05; bars sharing the same letter are not significantly different. * and ** indicate significant differences between each treatment and the control at p < 0.05 and p < 0.01, respectively. The same notation applies to subsequent figures

SPAD content in D. brandisii leaves under different treatments

SiO₂ NP concentration and the concentration × time interaction significantly affected SPAD values, whereas the main effect of treatment time was not significant (Table 2). SPAD values ranged from 38.20 to 48.73 across all treatments and sampling dates (Fig. 2). Low-to-moderate SiO₂ NP treatments generally increased SPAD values compared with CK, indicating an improvement in chlorophyll-related status. Among all treatments, T3 consistently showed the strongest positive response and maintained relatively high SPAD values throughout the experiment. The difference between T3 and the other treatments became more evident on days 10 and 15, suggesting that the beneficial effect of moderate SiO₂ NP application persisted over time. In contrast, T5 showed only a weak increase at the early stage and had the lowest SPAD value on day 15. These results suggest that moderate SiO₂ NP application enhanced leaf chlorophyll-related status, whereas excessive application weakened or reversed this positive effect.

Fig. 2.

SPAD content in D. brandisii leaves under different treatments

The content of nutrient elements in D. brandisii leaves under different treatments

C content in D. brandisii leaves under different treatments

As shown in Fig. 3, SiO₂ NP concentration and treatment time significantly affected the leaf carbon (C) content of D. brandisii cuttings, with two-way ANOVA revealing highly significant effects of concentration, time, and their interaction (F = 65.373, p < 0.01; F = 16.338, p < 0.01; F = 21.357, p < 0.01) (Table 2).

Fig. 3.

C content in D. brandisii leaves under different treatments

Leaf C content ranged from 390.18 to 572.40 g·kg⁻¹ across all treatments and sampling dates (Fig. 3). In general, foliar SiO₂ NP application altered leaf C accumulation, but the response varied with both concentration and time. At the early stage, low-to-moderate SiO₂ NP treatments increased C content compared with CK, with T2 and T3 showing relatively high values. On day 10, T2 showed the highest C content, whereas T3, T4, and T5 were relatively lower, indicating that the C response was not strictly proportional to SiO₂ NP concentration. By day 15, T1 and T2 maintained relatively high C contents, while CK remained comparatively low. Overall, these results indicate that SiO₂ NP application influenced leaf C accumulation, but the most favorable response occurred under low-to-moderate concentrations rather than under the highest concentration.

N content in D. brandisii leaves under different treatments

As shown in Fig. 4, different SiO₂ NP concentrations and treatment times significantly affected leaf N content in D. brandisii seedlings, with two-way ANOVA indicating a highly significant main effect of concentration and a significant main effect of time, whereas the concentration × time interaction was not significant (F = 18.754, p < 0.01; F = 7.545, p < 0.05; F = 0.936, p > 0.05) (Table 2).

Fig. 4.

N content in D. brandisii leaves under different treatments

Across all treatments and sampling dates, leaf N content ranged from 17.82 to 20.92 g·kg⁻¹ (Fig. 4). Compared with CK, moderate SiO₂ NP treatments generally increased leaf N content, especially under T2 and T3. The positive effect of T3 was evident across sampling dates, indicating that moderate SiO₂ NP application helped maintain relatively high N accumulation. In contrast, T5 showed relatively low N content at most sampling dates and was often close to CK, suggesting that excessive SiO₂ NP application did not further promote N accumulation. These results indicate that leaf N accumulation responded positively to moderate SiO₂ NP application, while the highest concentration provided limited benefit.

P content in D. brandisii leaves under different treatments

As shown in Fig. 5, different SiO₂ NP concentrations and treatment times significantly affected leaf P content in D. brandisii seedlings, with two-way ANOVA indicating highly significant main effects of concentration and time and a highly significant concentration - time interaction (F = 44.409, p < 0.01; F = 7.506, p < 0.01; F = 5.662, p < 0.01) (Table 2).

Fig. 5.

P content in D. brandisii leaves under different treatments

Compared with CK, SiO₂ NP application generally increased leaf P content, and this response was most pronounced under the T3 treatment (Fig. 5). Across the three sampling dates, T3 consistently produced the highest P content, indicating a stable positive effect of moderate SiO₂ NP application on P accumulation. T2, T4, and T5 showed intermediate responses depending on sampling time, whereas CK remained the lowest. The increasing trend of P content under T3 over time further suggests that an appropriate SiO₂ NP dose may enhance P accumulation or retention in D. brandisii leaves. Overall, T3 was the most effective treatment for promoting leaf P accumulation, while higher concentrations did not produce additional benefits.

K content in D. brandisii leaves under different treatments

Different SiO₂ NP concentrations and treatment times significantly affected leaf K content in D. brandisii seedlings, with two-way ANOVA indicating highly significant and significant main effects of concentration and time, respectively, as well as a significant concentration–time interaction (F = 10.361, p < 0.01; F = 70.237, p < 0.01; F = 2.431, p < 0.05) (Table 2).

Across all treatments, K content ranged from 6.31 to 10.03 g·kg⁻¹ (Fig. 6). Leaf K content showed a clear temporal pattern, generally decreasing on day 10 and increasing again on day 15. Compared with CK, SiO₂ NP treatments generally increased K content, but the magnitude of this increase varied among concentrations. T3 maintained relatively high K content across sampling dates and showed the most pronounced increase by day 15. T2 and T4 also showed positive responses at some stages, whereas T5 remained at an intermediate level and did not exceed the effect of T3. These results suggest that moderate SiO₂ NP application promoted K accumulation more effectively than excessive application.

Fig. 6.

K content in D. brandisii leaves under different treatments

C, N, P, and K stoichiometric ratios in D. brandisii leaves under different treatments

Under different SiO₂ NP concentrations, leaf SiO₂, C, N, P, and K contents in D. brandisii were significantly affected, with concentration-effect F-values of 35.671, 65.373, 18.754, 44.409, and 10.361, respectively (p < 0.01; Table 2). Two-way ANOVA showed that SiO₂ NP concentration significantly affected all measured stoichiometric ratios (p < 0.05), whereas treatment time significantly affected most ratios except SiO₂:P (p = 0.053) (Table 3).

Table 3.

Effects of SiO₂ nanoparticle concentration, treatment time, and their interaction on leaf stoichiometric ratios in D. brandisii seedlings

Indicator	Factor	F	p
SiO₂: C	Time	24.788	0.001
	Concentration	25.788	0.001
	Time × Concentration	12.364	0.001
SiO₂: N	Time	9.850	0.001
	Concentration	7.887	0.001
	Time × Concentration	1.347	0.244
SiO₂: P	Time	3.185	0.053
	Concentration	2.487	0.049
	Time × Concentration	1.719	0.114
SiO₂: K	Time	61.032	0.001
	Concentration	3.525	0.011
	Time × Concentration	1.819	0.092
C: N	Time	3.887	0.03
	Concentration	29.700	0.001
	Time × Concentration	16.316	0.001
C: P	Time	8.976	0.001
	Concentration	21.132	0.001
	Time × Concentration	9.504	0.001
C: K	Time	31.604	0.001
	Concentration	17.048	0.001
	Time × Concentration	8.303	0.001
N: P	Time	4.455	0.019
	Concentration	18.925	0.001
	Time × Concentration	3.473	0.003
N: K	Time	52.838	0.001
	Concentration	494.535	0.001
	Time × Concentration	5.140	0.001
P: K	Time	60.597	0.001
	Concentration	8.564	0.001
	Time × Concentration	2.781	0.012

F-values and p-values were obtained from two-way ANOVA. The sources of variation included SiO₂ NP concentration, treatment time, and their interaction. p > 0.05 indicates no significant effect, p < 0.05 indicates a significant effect, and p < 0.01 indicates a highly significant effect. SiO₂ NPs, silicon dioxide nanoparticles

Significant concentration × time interactions were observed for several ratios, including SiO₂:C, C:N, C:P, C:K, N:P, N:K, and P: K, whereas the interactions for SiO₂:N, SiO₂:P, and SiO₂:K were not significant. Overall, the stoichiometric responses showed a clear concentration-dependent pattern. Low-to-moderate SiO₂ NP treatments, especially T3, produced more pronounced changes in nutrient contents and stoichiometric ratios than the highest concentration treatment. Ratios involving SiO₂ reflected enhanced silicon accumulation relative to C, N, P, or K, whereas C: N:P: K ratios indicated shifts in nutrient balance under different SiO₂ NP doses. These results suggest that foliar SiO₂ NP application altered not only absolute nutrient contents but also the relative allocation patterns among SiO₂, C, N, P, and K in D. brandisii leaves (Fig. 7).

Fig. 7.

C: N: P: K stoichiometry in D. brandisii leaves under different treatments. Panels represent: (A) SiO₂:C, (B) SiO₂:N, (C) SiO₂:P, (D) SiO₂:K, (E) C:N, (F) C:P, (G) C:K, (H) N:P, (I) N:K, and (J) P:K

C, N, P, and K stoichiometry and SPAD values in D. brandisii leaves under different treatments

As illustrated in Fig. 8, under different SiO₂ NPs treatments, the SiO₂ content, chlorophyll index (SPAD) and C: N: P: K stoichiometry in D. brandisii leaves were significantly interrelated (p < 0.05). SPAD was strongly and positively correlated with SiO₂, total N, and total P (p < 0.01), showed a weak but significant positive correlation with K (p < 0.05), and was not significantly related to total C. The ratios of SiO₂: C and SiO₂: N showed positive correlations with SPAD, suggesting that a moderate increase in SiO₂ relative to C and N favors chlorophyll formation; in contrast, the SiO₂: P ratio was significantly and negatively associated with SPAD (p < 0.05), implying that overly high values of this ratio may suppress chlorophyll accumulation. Overall, significant positive correlations were observed among C, N, P, and K elements, with the strongest relationships found between C-N, N-P, and P-K. This indicates a synergistic accumulation trend of these elements within D. brandisii. Among the major stoichiometric ratios, C: N showed a highly significant positive correlation with C: P, but a negative correlation with N: P. This reflected that changes in the inter-element ratios can affect the overall nutrient balance.

Fig. 8.

Relationships between SPAD values and C: N: P: K stoichiometry in D. brandisii leaves under different treatments

Phenotypic plasticity indices of C, N, P, and K stoichiometry in D. brandisii leaves under different treatments

The phenotypic plasticity index ranged from 0.045 to 0.435 (Fig. 9). On the 5th day, the C and P treatments showed the highest indices (0.318 and 0.345), whereas the N and N: K treatments had the lowest values (< 0.1), indicating that C and P strongly enhanced early plasticity, while N and N: K exerted inhibitory effects. On the 10th day, the indices associated with SiO₂, P, SiO₂:C, and C: P all exceeded 0.3 and became the main promotive factors, whereas N and N: K remained at the lowest levels, indicating that their inhibitory effects persisted. On the 15th day, the index related to C: P peaked again at 0.435, suggesting a pronounced and persistent promotive role of C: P in the later stage, whereas N, N: K, as well as SiO₂ and K, were mainly associated with inhibitory effects. Overall, phenotypic plasticity was jointly regulated by treatment type and duration, showing distinct stage-specific dominant factors. At the early stage (Day 5) after SiO₂ NPs application, plasticity was mainly driven by nutrient acquisition, with phosphorus (P), carbon (C), and their associated ratios (e.g. SiO₂: _C) playing dominant roles, reflecting a rapid plant response to basic nutrient supply. At the middle stage after SiO₂ NPs treatments (Day 10), regulation shifted towards the adjustment of nutrient proportions and balance, with the carbon–phosphorus ratio (C: P) and SiO₂-related traits becoming the major determinants, indicating that structural defence and nutrient partitioning were particularly important at this stage. At the late stage (Day 15), P became central, and the C: P ratio reached its maximum, with phenotypic plasticity being mainly governed by nutrient balance, particularly by P availability. Across all stages, N and the N: K ratio consistently suppressed plasticity, whereas the N: P ratio exerted a relatively stable promotive effect.

Fig. 9.

Phenotypic plasticity index of leaf C: N: P: K stoichiometric traits in D. brandisii leaves under different treatments

Principal component analysis of C, N, P, and K stoichiometric ratios in D. brandisii leaves under different treatments

Principal component analysis (PCA) was used to summarize the multivariate relationships among leaf SiO₂ content, SPAD values, C, N, P, and K contents, and their stoichiometric ratios under different SiO₂ NP treatments (Fig. 10). The first two principal components together explained 65.4% of the total variance, with PC1 and PC2 explaining 41.5% and 23.9%, respectively. Samples collected on day 5 were mainly distributed in the lower-left region of the PCA biplot and were associated with relatively stronger contributions of C-related ratios, including C: P, C: N, N: P, C: K, and N: K. Samples collected on day 10 shifted toward the upper-right region and were more closely associated with P, SiO₂, and SPAD. Samples collected on day 15 were mainly located in the lower-right region and were associated with K and SiO₂: _C. Overall, the PCA pattern suggested time-dependent shifts in the relationships among leaf C, nutrient elements, SiO₂, and SPAD values. These patterns should be interpreted as multivariate associations among measured traits rather than direct evidence of physiological progression or causal regulation.

Fig. 10.

Principal component analysis of leaf physiological and stoichiometric traits in D. brandisii seedlings under different treatments. Note: Triangles denote measurements at day 5, squares at day 10, and circles at day 15

Discussion

Effect of SiO₂ NPs on SiO₂ content in D. brandisii seedling leaves

Foliar SiO₂ NP application promoted leaf SiO₂ accumulation in D. brandisii seedlings in a concentration-dependent and optimum-dose pattern. Silicon dioxide (SiO₂) is a fundamental structural component of plant cell walls, where it enhances mechanical strength, improves tissue organization, and positively influences stress tolerance and overall growth. Compared with traditional silicon fertilizers, SiO₂ NPs, characterized by their small particle size and large specific surface area, may exhibit greater bioavailability and more efficient uptake by plants [40, 41]. Previous studies demonstrate that nano-silicon readily penetrates plant tissues through leaf stomata and the cuticle, promotes silicon accumulation, and enhance resistance to pathogens, insects, drought, and heavy metal stress [42, 43]. These attributes provide a strong rationale for applying nano-silicon to improve crop productivity and stress resilience.

Our results showed that foliar application of SiO₂ NPs significantly increased the SiO₂ content in D. brandisii leaves. Under the T3 treatment, leaf SiO₂ content reached 3.59% on the 15th day, representing a 48.7% increase compared with the control. This finding indicates that T3 was the most effective concentration for promoting SiO₂ accumulation in leaves under the present experimental conditions. These results are consistent with previous findings that exogenous nano-silicon enhances silicon absorption and expands the pool of bioavailable silicon in plants [44].

Notably, under the T5 treatment, although leaf SiO₂ content increased relative to the control, the magnitude of this increase was significantly lower than that observed under the T3 treatment. Moreover, compared with earlier stages, SiO₂ content under T5 showed a decline by the 15th day. This suggests that excessively high SiO₂ NP concentrations may not further improve silicon accumulation and may instead reduce silicon uptake or utilization efficiency. These observations are consistent with previous reports that high concentrations of nano-silicon may disrupt normal metabolic processes in plants, particularly those related to silicon absorption and translocation [45]. Possible explanations include nanoparticle aggregation on the leaf surface, limited internal translocation, or concentration-induced disturbance on nutrient and metabolic homeostasis, all of which warrant further investigation.

Nano-silicon exerts its effects primarily due to its small particle size and large specific surface area, which may facilitate contact with leaf surfaces and promote entry into plant tissues through stomatal and cuticular pathways. Once internalized, silicon is deposited in cell walls and epidermal tissues, forming a physical–biochemical barrier that enhances cell-wall mechanical strength and improves plant stress tolerance [46, 47]. In the present study, the intermediate SiO₂ NP concentration, T3, markedly increased leaf SiO₂ content in D. brandisii, indicating that an appropriate SiO₂ NP concentration can effectively promote silicon accumulation. In contrast, the highest concentration, T5, resulted in only a limited additional increase in SiO₂ accumulation and appeared to negatively affect physiological performance. This concentration-dependent response suggests that foliar SiO₂ NP uptake in D. brandisii may follow an optimum-dose pattern rather than a simple linear increase with external concentration. At moderate concentrations, SiO₂ NPs may remain sufficiently dispersed and accessible for foliar absorption, thereby enhancing silicon accumulation. However, excessive concentrations may increase particle aggregation or create surface loading on leaves, reducing effective absorption and disturbing internal nutrient transport. Thus, the lower response observed under T5 may reflect a shift from beneficial silicon supplementation to physiological burden.

Effect of SiO₂ NP on SPAD values and photosynthetic potential in D. brandisii seedling leaves

Moderate SiO₂ NP application improved SPAD-based chlorophyll status in D. brandisii leaves, whereas excessive application weakened this positive response. The SPAD value is a widely used indicator of leaf chlorophyll status and is closely related to photosynthetic potential. Nano-silicon is known to enhance plant photosynthetic performance and stress tolerance in numerous crop species [48, 49]. This positive effect is especially pronounced at moderate doses under environmental stress conditions [50–53].

In the present study, different SiO₂ NP concentrations significantly affected SPAD values in D. brandisii leaves. The SPAD value under the T3 treatment reached 48.73 on the 15th day, representing a 14.5% increase relative to the control, whereas the T5 treatment decreased SPAD to 38.20, which was lower than both the control and the other SiO₂ NP treatments. These results indicate that moderate SiO₂ NP application may improve leaf chlorophyll-related status, whereas excessive application may be detrimental. This concentration-dependent response is consistent with previous reports showing that moderate SiO₂ NP application can enhance photosynthetic performance, whereas excessive doses may suppress photosynthesis [54, 55]. Such inhibition at high concentrations may be associated with silicon over-accumulation, potentially affecting metabolic homeostasis and chlorophyll synthesis [56]. Mechanistically, SiO₂ NPs may influence SPAD values through their effects on mineral nutrient balance, nutrient interactions, and photosynthetic pigment formation [57]. Nitrogen is an essential component of chlorophyll molecules and photosynthetic proteins, while phosphorus participates in energy transfer and nucleic acid metabolism, and potassium contributes to stomatal regulation, osmotic adjustment, and enzyme activation [58–60]. The higher SPAD values observed under T3 may be partly related to improved N, P, and K accumulation and a more coordinated nutrient balance. In addition, moderate silicon accumulation may enhance leaf structural stability and help protect the photosynthetic apparatus, thereby supporting chlorophyll maintenance. In contrast, excessive SiO₂ NP application may increase particle aggregation or surface loading on leaves, which could reduce effective foliar absorption, disturb nutrient transport, and weaken chlorophyll-related physiological performance. Therefore, the SPAD increase under T3 is best interpreted as improved chlorophyll-related status and photosynthetic potential, whereas the decline under T5 may indicate a dose-dependent transition from beneficial silicon supply to physiological constraint. Since SPAD is an indirect indicator of chlorophyll status, future gas-exchange and chlorophyll fluorescence studies are needed to further verify these interpretations.

Effect of SiO₂ NPs on C, N, P, and K stoichiometry inD. brandisiiseedling leaves

Foliar SiO₂ NP application altered both elemental accumulation and C: N: P: K stoichiometric relationships in D. brandisii leaves, with the strongest coordinated response occurring under the T3 treatment.

C, N, P, and K constitute the basic elemental pool supporting plant growth and development, and their internal proportional relationships influence plant resource allocation and nutrient-use efficiency [61]. Previous research has shown that forest productivity is closely associated with nutrient uptake, nutrient return, and soil nutrient cycling, highlighting the importance of nutrient-use efficiency for maintaining long-term plantation productivity. The C: N ratio reflects the balance between carbon accumulation and nitrogen-supported metabolic activity, the N: P ratio is closely related to the relative utilization of N and P, and ratios involving Si, such as N: Si and K: Si, may help reveal how silicon deposition interacts with essential nutrient allocation [62, 63]. Previous studies have shown that SiO₂ NPs can improve photosynthetic efficiency and contribute to plant growth by regulating nutrient acquisition and distribution [64–66]. However, the concentration-dependent effects of silicon application on bamboo stoichiometry remain insufficiently understood, which provided the motivation for the present study.

Our results showed that SiO₂ NP application substantially modified the leaf stoichiometry of C, N, P, and K in D. brandisii, particularly affecting key ratios such as C: N, N: P, N: Si, and K: Si. With increasing SiO₂ NP concentration, the C: N ratio generally increased at moderate concentrations, indicating a shift in the relative balance between leaf C and N. This change may reflect increased C accumulation, decreased N accumulation, or their combined effects, rather than carbon accumulation alone. This pattern suggests that appropriate SiO₂ NP supply may promote carbon accumulation while maintaining nutrient balance. It may also indicate a shift toward structural investment, such as cell-wall reinforcement and silicon-associated deposition, rather than a simple increase in nutrient accumulation alone. This observation is consistent with previous reports that silicon addition can shift nutrient allocation by reinforcing structural defence mechanisms [67]. The most favorable stoichiometric response observed under T3 suggests that a moderate SiO₂ NP dose was most effective in coordinating carbon accumulation and nutrient balance. In contrast, the weaker response under T5 implies that excessive SiO₂ NP supply may constrain nutrient uptake or reduce nutrient-use efficiency. This result is consistent with studies showing that excessive silicon can disrupt nitrogen metabolism and reduce N use efficiency [68, 69].

In terms of the N: P ratio, a pronounced change was observed under the T3 treatment, suggesting that SiO₂ NP application altered the relative balance between N and P metabolism. However, because plant N: P thresholds vary among species, developmental stages, and environmental conditions, this change should be interpreted as evidence of altered N–P balance rather than direct proof of phosphorus limitation. Therefore, the potential interaction between silicon and phosphorus in D. brandisii requires further verification through nutrient-addition experiments, root morphology analysis, phosphatase activity, and nutrient uptake kinetics. In contrast, lower SiO₂ NP doses, such as T1 and T2, caused relatively smaller changes in N: P, which is consistent with reports that moderate silicon application can optimize the uptake of key nutrients, such as P and K, thereby promoting plant growth [70].

Overall, both the N: Si and K: Si ratios declined with increasing SiO₂ NP concentration, indicating that silicon accumulated more strongly relative to N and K under higher SiO₂ NP supply. This shift suggests that silicon-associated structural investment may become increasingly dominant as SiO₂ NP concentration increases. At moderate levels, such a shift may strengthen tissue protection and improve stress resistance [71, 72]; however, at excessive levels, it may reduce the relative allocation of growth-related nutrients and disturb nutrient-use efficiency. The rebound of some ratios, such as K: Si, on day 15 under T4 and T5 may reflect changes in nutrient redistribution, dry matter accumulation, or dilution effects during tissue development. These processes may be associated with structural developmental changes reported in previous studies [73, 74]. However, because lignin content, fiber traits, and leaf anatomical structure were not directly measured in this study, this interpretation remains hypothetical and should be verified in future studies. Detailed physicochemical properties of the SiO₂ NPs, such as zeta potential and suspension stability, were not directly measured and should be further considered in future studies.

Collectively, these findings demonstrate that SiO₂ NPs not only modified the absolute concentrations of nutrient elements in D. brandisii leaves but also reshaped multiple key stoichiometric ratios. The most favorable response occurred under the moderate T3 treatment, suggesting a coordinated relationship among silicon accumulation, leaf C accumulation, and nutrient allocation. In contrast, excessive SiO₂ NP application may disrupt this balance, leading to reduced nutrient-use efficiency and weaker physiological performance. These results indicate that SiO₂ NP application should be optimized carefully to enhance bamboo seedling growth without disturbing C: N: P: K stoichiometric homeostasis.

Comparison with other fertilizers and prospects

SiO₂ NPs should be regarded as a supplementary nutrient-regulation tool rather than a substitute for conventional fertilization. As a foliar-applied beneficial element source, SiO₂ NPs can enhance plant nutrient acquisition, strengthen stress tolerance, and stimulate growth, thereby serving as a potential tool for improving productivity [75]. Unlike traditional fertilizers, such as amino acid-based formulations, SiO₂ NPs may improve photosynthetic performance and plant growth by regulating silicon availability, cell protection, nutrient balance, and physiological resilience [76]. Conventional nitrogen fertilizers regulate plant nutrition through direct participation in metabolic processes, improving N uptake and use efficiency and facilitating the uptake of other nutrients in Phyllostachys edulis and Dendrocalamus latiflorus Munro [77, 78]. Previous research has also shown that different nitrogen forms can significantly influence seedling morphology and growth performance in widely cultivated tree species [79]. In contrast, potassium fertilization mainly regulates plant water status, maintains cell turgor, and modulates enzyme activity [80]. Despite their benefits, conventional fertilizers do not specifically target silicon-mediated structural protection or silicon-associated coordination of multiple nutrients. Given the role of silicon in photosynthetic regulation and mineral nutrient dynamics, SiO₂ NPs should be regarded as a complementary nutrient-regulation tool rather than a substitute for conventional fertilization [81].

While SiO₂ NPs can enhance nutrient absorption, increase stress resistance, and stimulate growth, their over-application may cause unintended adverse effects [82]. Previous studies have shown that excessive fertilizer inputs, particularly nitrogen, can lead to nutrient over-accumulation, inhibit the uptake of other nutrients, reduce drought tolerance, increase susceptibility to pests and pathogens, and ultimately result in growth retardation or nutrient disorders [83, 84]. Similarly, when silicon supplied by SiO₂ NPs accumulates excessively, it may disrupt normal metabolism, suppress the uptake of N, P, and other nutrients, and compromise plant growth and stress resilience [85]. Under high SiO₂ NP treatments, excessive silicon deposition or nanoparticle loading may also affect mineral nutrient balance, including nutrients involved in photosynthetic function, thereby reducing photosynthetic efficiency and weakening nutrient acquisition capacity.

This study identifies several productive directions for future research regarding foliar SiO₂ NP application in D. brandisii seedlings. The experimental period was relatively short, suggesting that long-term field trials will be important for understanding the effects of repeated or seasonal application. The present focus on leaf-level stoichiometric responses—while providing valuable mechanistic insights—invites complementary studies on biomass accumulation, root traits, gas-exchange parameters, chlorophyll fluorescence, and photosynthetic enzyme activities to bridge leaf-level observations with whole-plant productivity. Furthermore, although sonication was employed to ensure dispersion, direct characterization of particle-size distribution, zeta potential, and suspension stability would enhance our understanding of nanoparticle behavior. Collectively, future studies that integrate these approaches will be instrumental in establishing optimal SiO₂ NP application strategies for sustainable bamboo cultivation.

Conclusion

This study demonstrated that foliar SiO₂ NP application influenced leaf SPAD values, SiO₂ accumulation, nutrient contents, and C: N: P: K stoichiometric patterns in D. brandisii seedlings. Among the concentrations tested, 300 mg·L⁻¹ (T3) produced the most favorable response, whereas 500 mg·L⁻¹ (T5) resulted in discernible reductions in SPAD values and nutrient accumulation. These findings suggest that moderate SiO₂ NP application may serve as a supplementary nutrient-management approach for improving bamboo seedling quality, while excessive application should be avoided. In the context of nursery and forest management practices, moderate SiO₂ NP application is preferable to high-dose application, and foliar nano-silica should be integrated with conventional N, P, and K fertilization rather than used as a substitute. Prior to large-scale application, long-term field trials and environmental safety monitoring are indispensable for evaluating its effects on bamboo biomass, nutrient cycling, and plantation sustainability.

Abbreviations

ANOVA

Analysis of variance

CK

Control

SD

Standard deviation

SiO₂ NPs

Silicon dioxide nanoparticles

SPAD

Soil Plant Analysis Development

T1–T5

SiO₂ NPs were applied at concentrations of 100, 200, 300, 400, and 500 mg·L⁻¹

Authors’ contributions

1. J. was the experimental designer for this study, including conducting experiments, organizing data, and writing the initial draft of the paper. H. L. conceptualized, supervised resources. Y. Y. supervised resources. H. R. supervised resources. W. S. acquired funding. Y. L. conceptualized. L. L. conceptualized, supervised resources. Z. H. acquired funding, supervised resources. All authors have read and approved the published version of the manuscript. All authors have reviewed the manuscript and agreed to this version.

Funding

This study was jointly funded by the National Natural Science Foundation of China (NO. 32160415); Opening Foundation of Forestry First Discipline Degree program of Southwest Forestry University (LXXK-2025D17) and Xingdian Talent Support Plan Project (2022).

Data availability

The datasets generated and/or analyzed 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.