Silicon modifies C:N:P stoichiometry and improves the physiological efficiency and productivity of sorghum grown under nutritional sufficiency.

doi:10.21203/rs.3.rs-1425073/v1

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Silicon modifies C:N:P stoichiometry and improves the physiological efficiency and productivity of sorghum grown under nutritional sufficiency.

https://doi.org/10.21203/rs.3.rs-1425073/v1

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The benefits of silicon (Si) in plants under nutritional sufficiency may be involved in the modification of C:N:P stoichiometry, favoring homeostasis, cell metabolism and physiological processes, increasing biomass. However, studies in the grain sorghum are still scarce. Therefore, the objective was to evaluate the effect of Si supply on C:N:P stoichiometry, physiological response, and production of grain sorghum. The experiment was carried out in pots with four concentrations of Si: 0; 1.2; 2.4; and 3.6 mmol L-1. The increase in Si concentration linearly increased the dark green color index and stomatal conductance, although photosynthetic rate and transpiration increased up to the concentration of 1.9 and 2.0 mmol L-1, respectively. The application of Si decreases C:Si, C:N e C:P stoichiometric ratios and favors photosynthesis, resulting in an increase in grain biomass. Dry matter was favored by increasing Si concentrations up to 1.4; 2.3; 2.1; and 2.2 mmol L-1 for root, shoot, whole plant, and grain, respectively. Thus, the results reveal that the benefit of Si in sorghum under nutritional sufficiency occurs due to the induction of optimization of C:N:P stoichiometry, consequently increasing metabolic efficiency and optimizing the efficiency of the use of C, providing increases in the photosynthetic and biomass production.

Silicon (Si) is a mineral that is commonly found in soils, but the levels available in soil solutions are relatively low in many weathered soils due to leaching, polymerization, and element export by crops¹. Si is absorbed as monosilicic acid, being present in plant tissues^2,3, and although not meeting the essentiality criteria, it is recognized as an important beneficial element for plants^4,5. Its main functions can be classified as structural and physiological^6,7, with a more significant effect on plants that accumulate the element, such as grain sorghum (Sorghum bicolor L. Moench)^8,9.

The structural role played by Si is related to the incorporation of the beneficial element into cell walls, such as opals, which are also called phytoliths (SiO₂ nH₂O)^6,10.After Si absorption, this element is retained in the leaves, where some of the organic compounds can be replaced by the incorporation of Si in plant tissues, resulting in an increase in dry matter production and a decrease in carbon (C) contents, as verified in some species such as rice¹¹, wheat¹², sugarcane ^13–15, and forage¹⁶.

This substitution of C for structural Si in the cell wall stands out as one of the main advantages of silicate fertilization for plants, as it represents energy savings of up to 80%¹⁷. The value of one mole of ATP per mole of SiO₂ deposited is admitted as the cost of silicification¹⁸, while five moles of ATP and two moles of NADPH per mole of C assimilated are adopted as the minimum requirement for other growth processes ¹⁹.

Thus, the increase in Si incorporation in some species and mainly in Si-accumulating species such as sorghum can influence the stoichiometry of C:N:P:Si in different tissues (leaves, stems, and roots), as verified in Phragmites australis²⁰ and in sugarcane^13–15 and forages ¹⁶. Among the main physiological benefits of supplying Si to plants, the increase in chlorophyll content, which was observed in wheat plants grown in a saline environment, can be highlighted due to the integrity and stability that it provides to the cell membrane, ensured by the ability of Si to stimulate the production of antioxidant compounds²¹. This same effect was observed in rice plants under favorable cultivation conditions²², which can be explained by the morphological changes of the plant provided by the greater increase of structural Si supplied to the leaves, favoring a better light interception by the plant.

Si application also provides physiological changes, increasing stomatal conductance and photosynthetic activity, as verified in sorghum^8,23, for its action as an activator of the enzymatic antioxidant defense system, which reduces the degradation of organic compounds involved in the photosynthetic apparatus.

Given these biological benefits of Si in plants, it is known that it is a mitigating agent of different stresses in several species, including sorghum^24–30. In plants under nutritional sufficiency, it is possible that Si may also benefit their physiological attributes. However, energy savings may be occurring in plants before the application of Si by decreasing the C content in plant tissues, as aforementioned for some species. These plants may be optimizing the use of carbon by inducing a stoichiometric homeostasis involving carbon, nitrogen, and phosphorus, which are structural nutrients, thus favoring carbon metabolism and the growth of sorghum plants, although proof is needed.

Given the above, it is assumed that Si can be a vital element in optimizing the productivity of sorghum, which is a crop with nutritional importance for being a source of protein and energy, besides being a gluten-free and low-cost. Sorghum is mainly cultivated in hot and dry regions around the world, in large-scale commercial operations and small farms³¹. In this context, the hypothesis that the supply of Si modifies the C:N:P:Si stoichiometry, favoring the physiological responses and improving the growth and grain production of grain sorghum (Sorghumbicolor L. Moench) cultivated under nutritional sufficiency arises.

Once these hypotheses are accepted, it will be possible to better understand the biological role played by Si in the elementary stoichiometric homeostasis of the sorghum culture and support the expansion of the use of Si in the culture, ensuring an increase in the production of sustainable biomass, as there are many regions with soils that present low Si contents available, which is an element that presents no risks to the environment.

Therefore, this research was carried out aiming to evaluate the effect of Si supply via nutrient solution (roots) on C:N:P:Si stoichiometry and to verify its effect on grain production and physiological responses in grain sorghum plants.

Si, C, N, and P concentration in the plant.

The supply of silicon (Si) influenced the concentration of Si, carbon (C), nitrogen (N), and phosphorus (P) in the leaves, stems, and roots of sorghum plants, except for N and P (stem and roots) (Fig. 1). The increase in the concentrations of Si supplied to sorghum plants increased the concentration of N and P in leaves and Si in leaves, stems, and roots. However, there was a decrease in the concentration of C in leaves, stems, and roots. The highest concentration of Si, C, N, and P were observed in the leaves compared to the stem and root.

<<Figure 1>>

Stoichiometric relationships.

All stoichiometric ratios (C:Si, C:N, C:P, and N:P) were influenced by increasing Si concentrations in plant parts (leaf, stem, and root), except for stem (C :P) and root (N:P) (Fig. 2). With the exception of the N:P ratio (Fig. 2D), all stoichiometric ratios decreased with increasing supplies of Si. The C:Si ratio decreased by up to 90% at the Si concentration of 3.6 mmol L^− 1 Si compared to the control treatment (no Si supply), especially in leaves (Fig. 2A). Additionally, there were differences between the plant parts analyzed, where the root presented the highest means, except for the C:Si ratio (Fig. 2A).

<<Figure 2>>

Accumulation of Si, C, N, and P in the plant.

Increases in Si concentrations influenced the accumulation of Si in different plant (Fig. 3A), with no differences being observed in the accumulation of C, N, and P (Figs. 3B, 3C, and 3D). As expected, the greatest accumulation of Si occurred in the leaf, followed by the roots.

<<Figure 3>>

The accumulation of Si, C, N, and P in the plant shoot (Fig. 4) followed the same pattern observed in the different plant (Fig. 3). The accumulation of Si in the shoot increased by approximately 400% at the concentration of 3.6 mmol L^− 1 compared to the control treatment (without Si supply) (Fig. 4A), while the accumulation of C, N, and P was practically unchanged by increasing Si concentrations supplied to sorghum plants (Figs. 4B, 4C, and 4D).

<<Figure 4>>

Physiological responses and production.

The increase in Si concentrations supplied to sorghum plants significantly influenced the photosynthetic rate (A), stomatal conductance (gs), transpiration rate (E), dark green color index (DGCI), and biomass production (grains, roots, and shoots) (Fig. 5). On the other hand, 1000-grain weight was not significantly impacted by the supply of Si to sorghum plants (Fig. 5E).

<<Figure 5>>

The means of variables A, E, and biomass production reached the maximum values observed at the concentrations of 1.9, 2.0, and 2.2 mmol L^− 1 Si, with means equal to 51.94, 6.44, and 62.38, respectively (Figs. 5A, 5C and 5F). Regarding the variables gs and DGCI, there was a linear increase (p < 0.01) along with increasing Si concentrations. The benefit of Si in the leaf architecture is visible at the concentration of 1.2mmol L^− 1 Si compared to the control plant (without Si) (Fig. 6).

<<Figure 6>>

Multivariate analysis.

Hierarchical clustering analysis. The hierarchical clustering analysis of the leaf (Fig. 7a) and stem (Fig. 7b) showed similar results for the treatments, which were divided into the two following groups: the first group, consisting only of treatments with the absence of Si (0.0 mmol L^− 1 of Si); and the second group, consisting of treatments that received Si (1.2; 2.4; and 3.6 mmol L^− 1). It was also verified that there was the formation of two subgroups in the second grouping of treatments, with the formation of the first subgroup consisting only of the concentration of 1.2 mmol L^− 1 Si and the second subgroup consisting only of the concentrations of 2.4 and 3.6 mmol L^− 1 Si (Figs. 7a and 7b).

For the response variables of leaves, the formation of two groups was verified; the first group was formed by the isolated subgroup of N:P and the subgroup of C:N, C:Si, C concentration, and C:P (Fig. 7a). The second group was divided into the following two subgroups: concentrations and accumulations of P and Si, accumulation of C and DGCI; and concentration and accumulation of N, E, gs, A, and grain biomass. In addition, high dissimilarity was observed for stoichiometric ratios (N:P, C:N, C:Si, C:P) and the C concentration at.4 mmol L^− 1 Si, which is the concentration that showed greater similarity with grain biomass. Physiological responses (E, gs, and A) increased as a function of Si application, expressing greater similarity at the concentration of 1.2 mmol L^− 1, while the accumulation and concentration of N showed greater similarities at the concentration of 2.4 mmol L^− 1. Furthermore, the variables DGCI, Si concentration, and accumulation of P, C and Si were favored by greater similarity with the concentration of 3.6 mmol L^− 1 Si (Fig. 7a). In the stem, the first group consisted of concentration and accumulation of C and P and the stoichiometric ratios of C:N and C:Si, while the second group consisted of the subgroup of E, gs, and A and the subgroup of the C:P and N:P stoichiometric ratios, concentrations, and accumulation of Si and N, DGCI, and grain biomass (Fig. 7b). The responses of concentrations and accumulations of C and P and the C:N and C:Si stoichiometric ratios showed similarity with the concentration of 0.0 mmol L^− 1 Si, while the concentrations and accumulations of N and Si and C:P and N:P stoichiometric ratios were favored at the highest Si concentration of Si (3.6 mmol L^− 1).

The clustering analysis of roots showed the formation of the two following groups for the treatments: the first group consisted of the concentrations of 2.4 and 3.6 mmol L^− 1 Si and the second group consisted of the concentrations of 0.0 and 1.2 mmol L^− 1 Si (Fig. 7c). Regarding the independent variables in the root, there was the formation of the two following groups: the first group consisted of the concentrations and accumulations of P and Si and the DGCI. and the second group consisted of the subgroup with C:N ratio, E, gs, A, and grain biomass and the second subgroup, with the concentrations and accumulations of C and N and the stoichiometric ratios of C:Si, C:P, and N:P. It was also found that the C concentration and the stoichiometric ratios of C:P and N:P in the root expressed greater similarity with the 0.0 mmol L^− 1 Si concentration, while the concentration and accumulation of N were more favored by the concentration of 1.2 mmol L^− 1 Si (Fig. 7c). However, P concentration and C:N ratio expressed greater similarity with the 2.4 mmol L^− 1 Si concentration, while Si and P accumulations were more favored by the Si concentration equal to 3.6 mmol L^− 1 Si (Fig. 7c).

<<Figure 7>>

Principal component analysis. Principal component analysis (PCA) in the leaf (Fig. 8a), stem (Fig. 8b), and root (Fig. 8c) explained 89%, 97%, and 90%, respectively. The PCA of leaves indicated a relationship between physiological variables (E, gs, and A), concentration and accumulation of N, and grain biomass, with concentrations of 1.2 and 2.4 mmol L^− 1 Si, while C concentration and stoichiometric ratios (N:P, C:P, C:Si, and C:N) showed an association in the 0.0 mmol L^− 1 Si concentration and the variable responses of P and Si concentrations, accumulations of C, P, and Si and DGCI were related with the concentration of 3.6 mmol L^− 1 Si.

For the stem, PCA indicated that the concentration and accumulation of Si were related with the concentrations of 1.2 and 2.4 mmol L^− 1 Si (Fig. 8b). It was also verified that the concentration and accumulation of N in the stem were more strongly related with the concentrations of 2.4 and 3.6 mmol L^− 1 Si, while the stoichiometric ratios of C:P and N:P were associated with a higher Si concentration (3.6 mmol L^− 1). The PCA of roots indicated that concentrations and accumulations of P and Si were associated with the concentrations of 2.4 and 3.6 mmol L^− 1 Si (Fig. 8c). Furthermore, it was found that the stoichiometric ratios of C:Si and C:N in the root were strongly related to the concentration of 1.2 mmol L^− 1 Si.

<<Figure 8>>

Si is known to increase the biosynthesis of photosynthetic pigments such as chlorophylls and carotenoids^13,32, which explains the benefit of Si at the concentration of 3.6 mmol L^− 1 compared to control plants by increasing the dark green color index (DGCI) by 23%, which is considered as an indirect measure of chlorophyll content (Fig. 5D). The greater production of pigments, in turn, resulted in a trend towards a higher photosynthetic rate (A) (Fig. 5A), which contributed to obtaining a greater production of grain biomass (Fig. 5F). This increase in plant physiological activity promoted by Si was contributed by the increased excitation of the photosystem II reaction centers^33,34, favoring photosynthetic efficiency.

It should be noted that the results of this study demonstrate the potential response of grain sorghum plants to the application of Si. However, it depends on the Si concentration used, highlighting the concentration of 2.2 mmol L^− 1, constituting the first specific indication for this species using the production of grain biomass, that is, the yield for this recommendation. This should provide the proper usage of Si in this species for future research involving this element.

Through multivariate analysis, the photosynthetic rate (A), grain biomass, and the concentration and accumulation of foliar N showed high similarity (Fig. 7A), as N participates in the synthesis and composition of chlorophyll and is essential in the synthesis of phosphoenolpyruvate carboxylase (PEPC-enzymes) and ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO)³⁵. On the other hand, Si can also cause an increase in the concentration and accumulation of N from changes in primary metabolism, promoting the translocation of amino acids from the source of the synthesis to other plant tissues³⁶.

As expected, Si accumulation in different parts of sorghum plant (Figs. 3A and 4A) linearly increased along with the Si concentrations applied, mainly in leaves (Fig. 3A), which is the main site of Si accumulation¹⁰. Si deposition in the plant tissue, known as opal or 'phytoliths', adds strength and rigidity to cell walls³⁷, consequently being able to modify plant architecture, making them more erect (Fig. 6), which may have contributed to the trend towards increasing A (Fig. 5A) and biomass production (grains, roots, and shoots) (Fig. 5F) due to the greater capacity of light interception by the leaf surface¹⁰.

The increase in the concentration and accumulation of Si in the leaf and root also provided an increase in the concentration and accumulation of P in these plant organs, while in the stem, the concentration and accumulation of P showed a greater association in the absence of Si application (Fig. 8). The importance of Si in increasing P accumulation in the plant, especially in the leaves, has been reported by some authors. The effect of Si on P absorption occurs as this beneficial element increases the expression of genes related to P transporters in sorghum³⁰ and wheat roots³⁸. Furthermore, Si can act in antioxidant mechanisms^30,39, favoring the maintenance of the electrochemical gradient in the plasma membrane by increasing the activity of H-ATPase⁵, favoring the absorption of nutrients, including P.

C:P and N:P stoichiometric ratios in the stem were related to the increase in Si concentrations (Fig. 7b and 8b). This may have occurred as there is a translocation of metabolic energy gains to the leaves, causing a decrease in the concentration of P in sorghum stems, and consequently resulted in an increase in the C:P and N:P stoichiometric ratios of sorghum stems.

The effect of Si on plant gas exchange may be related to the species, environmental conditions⁴⁰, and concentrations used. Changes in morphophysiological characteristics as a response to changes in cell rigidity by the action of Si, consequently providing changes in plant growth, have already been verified in other species such as rice⁴¹ and sugarcane⁴².

On the other hand, excess Si induces a thick layer, due to the saturation of this element, an increase in leaf phytoliths, and a reduction in stomatal opening, hindering the diffusive process of gas exchange^43,44. Thus, the reductions in A values from the concentration of 1.9 mmol L^− 1 Si (Fig. 5A), associated with decreases in the accumulation of C in the plant (Figs. 3B and 4B), consequently decreased total biomass production (TDM, Fig. 5F). Additionally, the lowest mean TDM from this Si concentration onwards, associated with the stabilization of nitrogen (N) and phosphorus (P) concentration (Figs. 1C and 1D), also contributed to the absence of effects of Si on N and P accumulations in the plant (Figs. 4C and 4D).

Linear reductions in the C:Si, C:N, and C:P stoichiometric ratios in the different plant parts (Fig. 2A, 2B and 2C) are consequences of the linear reduction in the C concentration in the plant (Fig. 1B) and increases in concentration of Si, N, and P in the plant (1A, 1C and 1D). In a recent study, Frazão et al.¹³ found a reduction in the C concentration in different sugarcane tissues as the Si supply increased, with a consequent reduction in C:Si, C:N, and C:P stoichiometric ratios, as also observed in this study (Fig. 2A, 2B, and 2C). Unlike other stoichiometric ratios, the N:P ratio increased with increasing Si supplies (Fig. 2D), which resulted in a higher N concentration in the plant (Fig. 1C) compared to P concentration (Fig. 1D), a fact that was also observed in other species as a function of Si supply in quinoa plants⁴⁵.

The relevance of Si in elemental stoichiometry involving C in sorghum plants is better understood with a multivariate study. The reduction in the C concentration in the plant (Fig. 1B) also influenced the clustering of variables, and C:Si, C:N, and C:P stoichiometric ratios showed greater dissimilarity as the Si concentration increased, with these variables being in distant groups in leaves (Fig. 7a), stems (Fig. 7b), and roots (Fig. 7c). The greatest distance between C:Si, C:N, and C:P stoichiometric ratios as a function of the Si concentration, obtained by the cluster analysis of leaf variables (Fig. 7a), was observed at the concentration of 2.4 mmol L^− 1 Si. On the other hand, in this same Si concentration, it was also observed that the increase in the production of grain biomass is related to a decrease in the C:Si, C:N, and C:P stoichiometric ratios. The beneficial effects of Si on stoichiometric ratios, photosynthetic processes, and grain biomass production is reinforced by the hierarchical grouping of treatments in leaves and stems, indicating the formation of two dissimilar groups (without and with Si fertilization) as a result of the biological action of Si in sorghum. The results reinforce the importance of Si even in plants without the occurrence of stress, showing that it should be included among the elements that have a great influence on plant life¹⁰.

In the present research, we unveiled that the optimal stoichiometric homeostasis in grain sorghum plants at the Si concentration of 2.2 mmol L^− 1, which resulted in the optimal production of grain biomass, is associated with stoichiometric ratios that varied according to the analyzed organ, as follows: C:Si (leaf: 38; stem: 63; and root: 32), C:N (leaf: 31; stem: 19; and root: 32), C:P (leaf: 133; stem: 168; and root: 273) and N:P (leaf: 4; stem: 11; and root: 11). The C:Si stoichiometric ratio is noteworthy for being very narrow in the leaf and root and wide in the stalk, possibly indicating a greater substitution of C for Si. Therefore, C is more concentrated per unit of Si in cells of leaf and root organs. These organs, especially in leaves, may be generating a metabolic energy saving resulting from directing the energy balance towards other metabolic processes, favoring photosynthesis and attributing greater biomass production to the plants. These effects can be reinforced by the results of hierarchical grouping in the leaf and metabolic sites of the plant, indicating that Si decreases the studied stoichiometric ratios and, concomitantly, favors photosynthetic processes (Figs. 7a and 8a).

Therefore, our research indicated that Si promoted the homeostasis of structural nutrients that are known to be vital for the physiological process, such as N, as part of chlorophyll and enzymes, and P, as a constituent of nucleotides, phospholipids, and other compounds³⁵. This directly favored the efficient use of C, which is evidenced by the increase in photosynthesis and the consequent, increase in the growth and production of biomass in the sorghum crop induced by its high capacity for Si absorption, thus confirming the hypothesis of this research.

The direct implication of this research is that the indication and expansion of the use of Si in the sorghum crop, even when under nutritional sufficiency, should favor the production of grain biomass or the sustainable productivity of this species without causing risks to the environment, especially in soils with low Si contents, which predominantly occurs in regions where this crop is grown.

Nevertheless, the main mechanisms involved in the responses of grain sorghum under different Si concentrations still need to be further explored, and studies at the proteomic level are suggested to understand the role played by Si in the expression of genes involved in the absorption and efficiency of use of C, N, and P, that is, in the metabolism of these elements that are so important to the physiological processes of plants.

The study showed that grain sorghum is responsive to Si up to a concentration of 2.2 mmol L^− 1 by increasing the N:P stoichiometric ratio and decreasing the C:Si, C:N, and C:P ratios, regardless of the plant part, at the same time favoring physiological aspects of sorghum. Thus, it is unveiled that the benefit of Si in sorghum plants under nutritional sufficiency occurs due to the induction of a new C:N:P stoichiometric homeostasis, consequently increasing the metabolic efficiency and optimizing the efficiency of the use of C, increasing photosynthesis and biomass and grain production.

Growth conditions and experimental design.

An experiment was carried out in a greenhouse with grain sorghum using a soilless cultivation system. During the development of the experiment, temperature and relative humidity were recorded using a thermo-hygrometer, obtaining means of 35.9 ± 11.4°C; 19.3 ± 8.5°C; 76 ± 23%; and 32 ± 22% for maximum temperature and minimum temperature and maximum relative humidity and minimum relative humidity, respectively (Fig. 9).

<<Figure 9>>

Treatments consisted of the following four Si concentrations: 0; 1.2; 2.4; and 3.6 mmol L^− 1, arranged in a completely randomized design, with six replicates. The Si source used was potassium silicate (SiK), Diatom® (128 g L^− 1 Si; 126.5 g L^− 1 K₂O and pH 12). Si was added to the nutrient solution⁴⁶, the Fe source was modified to Fe-EDDHMA, and the pH value of the solution was adjusted between 5.5 and 6.5 with the addition of the HCl solution (1 mol L^− 1), being immediately supplied to the plants. The potassium content between treatments was balanced by adding KCl.

The experimental unit consisted of a polypropylene pot with capacity of 7 dm³ (upper diameter: 16cm; lower diameter: 11 cm; height: 33cm) filled with 6 dm³ of sand previously washed with running water, HCl solution (1%), and deionized water. Six seeds were distributed per experimental unit and thinning was carried out 21 days after emergence, maintaing one plant per pot.

The plants were irrigated with deionized water after sowing up to five days after emergence. Then, the application of a nutrient solution⁴⁶ at 10% of the concentration indicated by the authors began. Every seven days, the concentration was increased by 10% until reaching 70% of the indicated concentration, which was maintained until the end of the experiment. The nutrient solution was applied to maintain 70% of the substrate water holding capacity.

The substrate was drained once a week to eliminate excess salts. During substrate drainage, 700 mL of deionized water was added to each pot, inducing the drainage of 400 mL of nutrient solution, which was discarded. After two hours, a new nutrient solution was added to the plants.

Leaf gas exchange and dark green color index.

At 60 days after sowing (DAS), in the morning (between 9:00 and 11:00 h), physiological attributes were evaluated in the middle third of the first fully expanded leaf.

The physiological evaluations consisted of non-destructive analyses in which the net photosynthetic rate (A), transpiration (E), and stomatal conductance (gs) were measured under saturating light using a portable system to measure CO₂ and CO₂ exchanges (LcPro-SD, ADC BioScientific Ltd., Hoddesdon, UK) at a constant luminous intensity of 1200 µmol m^− 2 s^− 1 emitted by a blue/red LED light source. Leaf temperature was maintained between 32.63 ± 0.77 ºC and measurements were taken with the natural concentrations of CO₂ in the air (between 400 ppm).

In addition, the dark green color index was measured with using the OptiSciences® CCM-200 chlorophyll content meter, whose measurement unit is CCI (chlorophyll content index), which presents the value that is proportional to the amount of chlorophyll in the sample.

Evaluations of biomass production and shoot dry matter.

After the physiological maturation of the grains, panicles were harvested to determine yield with biomass being adjusted to the water content of 13%, and a mass of one thousand grains.

On the same occasion, the plants were harvested two centimeters above the substrate surface and divided into leaf, stem, and root. The collected material was washed in running water, neutral detergent (Extran® 1%), acidic solution (HCl 1%), and distilled and deionized water, placed in paper bags, and submitted to a forced air ventilation oven at 65 ± 5°C until the stability of the dry mass was obtained. Afterwards, the samples were weighed on a precision balance.

Chemical analyses and stoichiometry.

After weighing, the material was ground in a Wiley mill and subjected to chemical analysis. Nitrogen (N) and phosphorus (P) contents were analyzed according to Bataglia et al. (1983). Carbon analysis (C) was performed using the Walkley-Black method with external heat, according to Tedesco et al.⁴⁷. The silicon content (Si) was determined according to the methodology described by Korndörfer et al.⁴⁸. The accumulation of C, N, P, and Si was calculated from the product of dry mass by its respective concentration in each plant tissue evaluated.

Statistical analysis.

Data were subjected to analysis of variance (p < 0.05) and, when significant, a polynomial regression study was performed, choosing the model significant by the F test (p < 0.05) and with a higher coefficient of determination. Univariate analyzes were performed using Sisvar49. Multivariate analysis of hierarchical clustering and principal components was performed, using the similarity coefficient and simple-linkage clustering as group connection algorithms for hierarchical cluster analysis and the data correlation matrix for principal component analysis. For the processing of multivariate analysis, the Python programming language (version 3.9.7; Python Software Foundation) was used.

Acknowledgements

The support of the São Paulo State University (UNESP) is gratefully acknowledged.

Author contributions

J.S.C, J.J.F and J.P.S.J. conducted the experiment and wrote the primary version of the manuscript. The M.G.C. and J. J.F. contributed to the data analysis, while M.G.C and J.P.S.J performed the plotting of the graphs. All authors contributed to the review of the manuscript. The design, administration and fundraising of the experiment was carried out by R.M.P.

Competing interests

The authors declare no competing interests.

Additional information

Correspondence and requests for materials should be addressed to M.G.C.

The experimental research was carried out in compliance with relevant institutional, national and international guidelines and legislation.

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No competing interests reported.

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Silicon modifies C:N:P stoichiometry and improves the physiological efficiency and productivity of sorghum grown under nutritional sufficiency.

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