Differential response of growth and C:N:P stoichiometry to Si supply between bamboo and other tree seedlings

doi:10.21203/rs.3.rs-1988269/v1

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Differential response of growth and C:N:P stoichiometry to Si supply between bamboo and other tree seedlings

https://doi.org/10.21203/rs.3.rs-1988269/v1

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Aims

Silicon (Si), while not an essential element for plant growth, can be important for high Si-accumulating Poaceae, such as Moso bamboo. However, other trees do not actively take up dissolved silicic acid [Si(OH)₄] from the soil, likely because they have fewer or no specific Si transporters in their roots. It is unclear what causes the different growth and nutrient status between bamboo and other trees under varying Si supply. To explore the influences of Si availability on the growth, photosynthesis, nutrient status and C:N:P stoichiometry of bamboo and other trees.

Methods

We used one-year seedlings of P. pubescens, P. bournei, S. superba and C. lanceolata in a pot experiment where three widely differing levels of silicon were supplied, and measured growth traits, photosynthetic gas exchange properties and C:N:P stoichiometry of seedling responses to three levels Si supply and analyzed the impacts of Si supply on growth and nutrient status of bamboo and tree saplings.

Results

We found that Si increased the biomass production of P. pubescens seedlings with the higher concentration of Si supply, likely by improving its photosynthesis and nutrient status net photosynthetic rate, which contrasted to the seedlings of P. bournei and S. superba. In addition, we found that C concentrations of aboveground tissues in P. pubescens declined with increasing Si supply, likely due to a partial substitution of organic C compounds by Si. We also found that Si treatments increased the foliar C:N stoichiometry in the seedlings of P. bournei and S. superba through altering their concentration of C and N, but did not affect the C:N or N:P stoichiometry of C. lanceolata and P. pubescens.

Conclusions

Si elicited either a positive or negative effect on plants, such as improve or weaken photosynthetic capacity, increase or decrease the concentration of C and N in plants, depending much on plant species and the ambient supply level of Si in the environment. These results have implications for assessing the growth and nutrient status between bamboo and other trees (i.e, high Si-accumulating plants compared to other plants) when Si availability is altered in ecosystems, such as when Si availability in ecosystems is altered by bamboo expansion.

silicon supply

silicon accumulation

photosynthetic capacity

C: N: P stoichiometry

plant growth

Silicon (Si) supply improved the biomass production and photosynthesis of P. pubescens seedlings, which was in contrast to our findings for other tree seedlings.
C concentrations of aboveground tissues in P. pubescens declined with increasing Si supply, likely due to a partial substitution of organic C compounds by Si.
Si supply increased the foliar C:N stoichiometry in the seedlings of P. bournei and S. superba through altering their concentration of C and N, but did not affect the C:N:P stoichiometry of P. pubescens and C. lanceolata.

Silicon (Si), the second most abundant element in the Earth’s crust after oxygen, is released through the weathering of minerals, and some fractions contribute to biogeochemical cycles across long time sclaes (Struyf et al. 2009). Si can also regulate global CO₂ concentrations through plant-induced silicate weathering (Struyf et al. 2009, Keller et al. 2012) and occluding carbon within phytoliths resistant to decomposition (Conley 2002, Song et al. 2013). Higher plants can accumulate Si as a non-essential but beneficial element, which differs greatly between plant species because of differences in Si uptake by the roots (Ma and Yamaji 2006). Active, passive, and exclusive mechanisms if Si uptake in plant species, therefore, are classified as high-, intermediate-, and non-accumulators, respectively (Cornelis et al. 2010).

Moso bamboo (Phyllostachys pubescens) is a Si-accumulating plant and deposits richer phytoliths in tissues compared to trees (Lux et al. 2003, Umemura and Takenaka 2014). Indeed, Liu et al. (2022) found that bamboo can actively uptake dissolved silicic acid [Si(OH)₄] from soil via specific Si transporters in abundant fine roots, which contributed to improving its strength and resistance to biotic or abiotic stresses. In addition, bamboo has enormous potential to expand into neighboring (secondary) forest ecosystems and shift plant community composition, due to a strong leptomorphic (running) rhizome system (Isagi and Torii 1998, Ding et al. 2006, Lima et al. 2012). Bamboo expansion is a widespread phenomenon in subtropical regions. It has been reported that bamboo expansion altered Si pools and fluxes in forest ecosystems, particularly Si availability in soil (Liu et al. 2022). However, impacts of altering Si availability on the growth and stoichiometry of bamboo and other trees in forests following bamboo expansion are still unknown.

Generally, Si availability is determined by the concentration of non-crystalline Si in soil, which is dissolved relatively easily and the form most easily absorbed and utilized by plants; uptake of Si in this form can play an important role in plant development (Sauer et al. 2006, Klotzbücher et al. 2016). Si supply can also improve Si availability in agricultural and grassland ecosystems (Haynes 2017), which can impact plant production. For example, Si was associated with high growth rates of rice and wheat (Greger et al. 2018, LI et al. 2018). Other studies found that Si promotes plant growth and increases the number of branches, resulting in higher production of aboveground biomass (Liu et al. 2012). Indeed, Si improved the dry matter, nutrient accumulation, and grain yield was observed in some crop plants (Chen et al. 2002, Jinger et al. 2022).

Si can also play an important role in improving plant photosynthesis and modifying C:N:P stoichiometry. For example, Si can mitigate some stressors in plants, promoting photosynthetic capacity and improving physiological processes due to nutrient accumulation and investment to strength and rigidity (Epstein 2009, Maghsoudi et al. 2016). Photosynthetic capacity is generally closely linked to leaf N and P content, because both largely affect CO2 assimilation capacity of plants through altering the concentration of enzyme and ATP (LI et al. 2018, Zhang et al. 2018). Silicon has been reported to increase net photosynthetic rate and chlorophyll content (LI et al. 2018, Verma et al. 2019), with significant impacts on leaf N and P content. On the other hand, there was a partial substitution of organic C compounds by Si in some plants because Si can play a role similar to C in leaf structure (Schaller et al. 2012a, Katz et al. 2021). In fact, there would be cheaper energy cost in plant defenses structure through Si rather than C (Jonas et al. 2010, Schoelynck et al. 2010). Some studies found that Si availability modifies nutrient use efficiency, C:N:P stoichiometry, and productivity of winter wheat through expanding its root-to-canopy ratio (Schaller et al. 2012a, Neu et al. 2017, Teixeira et al. 2020), whereas Si deficiency in soil could decrease plant growth and weaken its photosynthsis. Consequently, increasing doses of Si can alter the stoichiometric composition of plants and, in turn, improve key physiological aspects, such as net photosynthetic rate, nutrients accumulation, leading to increased growth. Some studies experimental outline benefits for grass or crop plants from exogenous Si, such as increasing biomass production and modifing nutrient stoichiometry (Schaller et al. 2012b, Meena et al. 2014); however, we still do not know whether Si is advantageous for the growth of bamboo and tree species, which are rarely studied.

Despite the benefits of Si for Si-accumulating plants, including increased plant rigidity and resistance under biotic or abiotic stresses (Ma and Yamaji 2006, Mandlik et al. 2020), Si might play different role in other plants in forests (Ma and Yamaji 2006). For example, Si might not have much benifit to the growth of trees due to their passive or exclusive mechanisms with respect to Si uptake, as Si absorption is generally determined by transpiration, which is different from Si-accumulating plants like bamboo (Cornelis et al. 2010). Therefore, we suspected there would be differential performance between bamboo and trees due to their varying mechanisms of Si uptake. How variation in silicon supply affects the growth, photosynthesis, and nutrient use efficiency of some grasses and crop plants has also been investigated in some detail (Schaller et al. 2012a, Neu et al. 2017, Teixeira et al. 2020), but little is known about different effects of Si on the growth and C:N:P stoichiometry of bamboo and other trees when Si supply varies, which limits our understanding of the responses of bamboo and other trees to altered Si availability in soil following bamboo expansion.

To explore the influences of Si availability on the growth, physiological characteristics, and C:N:P stoichiometry of bamboo and other trees, we selected one- year seedlings of P. pubescens, P. bournei, S. superba, and C. lanceolata and conducted a pot experiment using three different levels of Si application. We posed two a priori hypotheses. First, we hypothesized that (H₁) there would be different growth responses to silicon supply between bamboo and other trees due to their different mechanisms of Si uptake and transport. We predicted that Si supply would promote the biomass production of bamboo, which would increase with its Si supply level, whereas trees would exhibit no response to Si supply due to its passive mechanisms of Si uptake determined by transpiration. Second, we hypothesized that (H₂) Si supply would improve photosynthetic gas exchange and modify C:N:P stoichiometry of both bamboo and tree seedlings, and that these effects would be stronger in bamboo. We predicted this because bamboo can take up dissolved silicic acid [Si(OH)₄] from soil both actively and passively, unlike the passive mechanisms of Si uptake in other trees which was determined by transpiration. To test these hypotheses, we measured growth traits, photosynthetic gas exchange properties and C:N:P stoichiometry of seedling responses to three levels Si supply and analyzed the impacts of Si supply on growth and nutrient status of bamboo and tree saplings. Our work builds a better understanding of differences in the responses of a range of physiologically different and commercially and ecologically important plant species to Si supply, which helps us predict differential performance between bamboo and other trees due to altered Si availability following bamboo expansion.

2.1 Plant material, growth conditions, and experimental design

A pot experiment was conducted from March to November 2019 at Fujian Academy of Forestry Sciences, Fuzhou, Fujian, China (26.15°N 119.29° E). We selected four species, Phyllostachys pubescens, Phoebe bournei, Schima superba, Cunninghamia lanceolata (the mean height and diameter were 40cm and 4cm respectively), which were the dominant species associated with bamboo expansion in subtropical forests.

We calculated their mean biomass of each species before planted (n = 4). One-year seedlings were planted into the plastic pots (D: 30cm, H: 35cm) in January 2019, filled with 3.5 kg sieved and homogeneous soil per pot. All seedlings were grown under natural environmental conditions with the same temperature and light exposure, and then treated with three levels of Si supply in June: 0 (control), 0.2, and 0.4 mg per pot. Silicon (H₂SiO₃) was dissolved in 100 mL of deionized water, which increased Si availability in soil (Liu et al. 2011, Bin et al. 2015) (Fig. 1). We frequently relocated the position of the potted plants to prevent rooting underground, and reduce the difference in ambient environment, such as light and humidity. We sampled seedlings (leaf, stems, and roots) at 15, 30, 90 and 120 days after Si supplementation and simultaneously measured photosynthetic gas exchange properties. All sampled seedlings in varying intensities of Si supply were completely randomized with four biological replicates.

2.2 Measurement of Growth Traits

We measured each seedling's growth traits monthly, including height and diameter. Additionally, biomass increment ratio was calculated by the biomass increment / the initial value.

2.3 Photosynthetic gas exchange measurements

Photosynthetic traits, such as net photosynthetic CO₂ assimilation (A), transpiration rate (E), stomatal conductance (g_s), and internal CO₂ concentrations (Ci), were observed approximately 15, 60, and 120 days after Si supplementation, using an LI-6800 portable photosynthesis system (LI-COR Biosciences, Lincoln, NE, USA). For each Si supply treatment, photosynthetic traits were conducted between 09:00–11:00 a.m. (solar time) on treated and normal plants (four replicates each), which is when A was at its maximum and temperature was suitable inside the growth chamber. Photosynthetic photon flux density (PPFD) was set at 1000 µmol m^− 2 s^− 1, leaf temperature (25°C), and CO₂ concentration was 400 µmol mol^− 1.

2.4 Soil samplings

To determine soil chemical properties, such as the concentrations of Si C, N and P, we mixed soil in each plastic pot (about 300–400 g wet weight per sample). Then, all soil samples (n = 192) were pooled, air-dried, and ground through a 2 mm sieve (Table 3).

2.5 Si concentrations

At the end of the experiment, seedling samples (i.e., leaf, stem and root) were collected, washed, and fully dried (65°C) up to constant weight. Then, 100 mg of dried leaf powder from each sample was digested using sodium hydroxide fusion at 950°C in a muffle furnace, washed using 7 ml of oxidizing solution (HNO₃– 6 ml and 30% H₂O₂-1 ml) for half an hour (150°C—10 min and 180°C—20 min) (Lu 2000). Prior to analysis, the digested extract was diluted with deionized water up to 250 mL (final volume). In addition, we added 30 mL of 1M acid Na acetate buffer solution at pH 4.0 to 0.75 g soil in a 50 mL centrifuge tube, agitated the sample for 24 h, and centrifuged the sample to extract the soluble and exchangeable Si (Si_SOL / Acid Na-acetate-Si), which is the most easily absorbed form of Si utilized by plants (Sauer et al. 2006, Klotzbücher et al. 2016). Both digested samples were then analyzed using spectroscopy with the silicon-molybdenum blue colorimetric method and a molybdate–ascorbic acid procedure at a pH of 1.2 ~ 1.3 using an ultraviolet visible spectrophotometer (UV-5100) (Georgiadis et al. 2013, Song et al. 2013) calibrated with standard solution. All Si measurements were run in duplicate and taken the average, which variants were less than 5%.

2.6 C, N and P concentration

Concentrations of C and N in the aforementioned samples (i.e., leaves, stems, roots, and soil) were analyzed using a dry combustion analyzer (Vario EL, Elementar Analysensysteme GmbH, Langenselbold, Germany) with acetanilide as an external standard. All C\N measurements were run in duplicate and taken the average, which the average deviations of replicate analyses from the means were 1.1% for N and 0.2% for C concentrations, our data were presented the average. To extract P in samples, 200 mg of dried plant powder from each sample was digested using H₂SO₄ and H₂O₂ at 650°C for half an hour using a microwave digestion system (JKXZ06-8B, China), followed up with a deionized water wash (up to 100 mL final volume). Prior to analysis, all digested samples were then determined using spectroscopy using the molybdenum antimony anticolorism method and a molybdate–ascorbic acid procedure using an ultraviolet visible spectrophotometer (880nm, UV-5100), calibrated with a standard solution (Lu 2000). All C, N and P measurements were run in duplicate and taken the average.

2.7 Statistical analysis

Differences among three levels of Si concentration for each response variables (including growth traits, photosynthetic gas exchange properties and C: N: P stoichiometry) were determined using analysis of variance (ANOVA) and a protected least significant difference (LSD) test (Duncan 1955). We compared differences in biomass increment, net photosynthetic rate, the concentration of Si, C, N, P and C: N: P stoichiometry between three intensities of Si supply. For all tests, the criterion for significant differences was P < 0.05. All statistical analyses were performed using SPSS (IBM, SPSS 24.0., USA.), and graphs were created using Origin (OriginLab - Origin 2017., USA).

3.1 Impact of silicon supply on growth traits

We found that Si addition increased almost 17% and 26% of prime biomass of P. pubescens with the low and high concentration of Si supply, which were much higher than that of control. However, there were different performance responses to Si supply among other tree seedlings. We also found that the highest concentration of Si decreased the production of biomass, particularly in P. bournei, S. superba (F_{2, 21} = 7.884, P = 0.003) (Fig. 2).

3.2 Impact of silicon supply on photosynthetic gas exchange properties

There were different photosynthetic performances in response to Si supply between bamboo and other tree seedlings. We found that the low Si concentration (Si + 0.2) improved the net photosynthetic rate of P. pubescens, but decreased its intercellular CO₂ concentration. We also found that Si decreased photosynthetic properties of P. bournei significantly, including net photosynthetic rate and stomatal conductance, which was in contrast to S. superba. Finally, low and high Si additions both decreased stomatal conductance in C. lanceolata (Fig. 3), wherease not affect its other photosynthetic gas exchange properties, such as net photosynthetic rate, transpiration rate and intercellular CO₂ concentration.

3.3 Impact of Silicon supply on C:N stoichiometry in plants

Generally, Si additions were associated with equivalent increase in Si availability in the soil. However, we found that there was no significant difference in the concentration of Si_SOL, C, or N among Si supply levels (Figure S1). We found that the Si concentration of tissues in bamboo was 5–10 times higher than other plants. There was significant difference in the leaf Si concentration of P. pubescens among three intensities of Si supply, i.e., high Si addition increased the leaf Si concentration in bamboo (F_{2, 9} = 2.779, P = 0.041) (Table 1), whereas no significant difference in the Si concentration of other tree saplings among three intensities of Si supply. These results probably indicated that varying Si concentration in different plants depend much upon their different mechanisms for Si uptake and transport. However, Si supply treatments decreased the Si concentration of stems and roots in C. lanceolata seedlings were 35–50% (F_{2, 21} = 8.692, P = 0.002) and 48–60% (F_{2, 21} = 12.748, P = 0.000) respectively. We also found that the concentration of C and N in P. pubescens and P. bournei under low or high Si addition were lower than that of control, which indicated Si supply decreased the concentration of C and N in P. pubescens and P. bournei (Table 1), and there was no significant difference in the P concentration of saplings among three Si treatments.

Table 1

**The effect of varying silicon supply on the concentration of S i, C, N, P in different tissues of** P. pubescens, P. bournei, S. superba **and** C. lanceolata (n = 4)
Elements	Si treatment	P. pubescens			P. bournei			S. superba			C. lanceolata
Elements	Si treatment	Leaf	Stem	Root	Leaf	Stem	Root	Leaf	Stem	Root	Leaf	Stem	Root
Si	0	28.0b	17.2	60.9	6.2	17.2	5.3b	4.2	2.7	13.1	4.8	2.9a	14.9a
	0.2	28.7b	19.2	56.3	10.0	19.2	10.0ab	4.8	2.6	9.5	3.8	1.9b	7.8b
	0.4	37.0a	16.8	34.8	9.3	16.8	16.9a	4.7	2.3	9.7	6.6	1.5b	5.8b
C	0	44.3a	45.2a	37.1	48.4	45.2a	48.5a	47.0	47.4	46.8	47.3	47.4	47.9b
	0.2	43.6ab	44.5b	37.2	48.4	44.5b	47.4b	47.3	47.1	46.9	47.4	47.5	48.7a
	0.4	42.8b	44.6b	35.1	48.1	44.6b	46.7b	47.1	47.1	46.7	47.0	47.4	49.4a
N	0	1.8	0.4	0.6	1.7a	0.4	1.3ab	1.6a	0.5	0.6	1.2	0.5	0.7
	0.2	1.8	0.4	0.6	1.5b	0.4	1.4a	1.7a	0.5	0.7	1.2	0.5	0.7
	0.4	1.7	0.4	0.6	1.5b	0.4	1.2b	1.3b	0.5	0.8	1.3	0.5	0.7
P	0	0.79	0.71	0.52	0.62	0.71	0.71	0.36	0.69	0.69	0.74	0.51	0.40
	0.2	0.57	0.35	0.53	0.52	0.35	0.69	0.52	0.73	0.84	0.66	0.46	0.39
	0.4	0.62	0.61	0.53	0.48	0.61	0.71	0.28	0.71	0.70	0.78	0.59	0.36
Si:C	0	0.064	0.038	0.176	0.013	0.038	0.011b	0.010	0.006	0.028	0.010	0.006a	0.031a
	0.2	0.065	0.043	0.162	0.021	0.043	0.021ab	0.010	0.006	0.020	0.010	0.004b	0.016b
	0.4	0.087	0.038	0.101	0.019	0.038	0.036a	0.011	0.005	0.021	0.015	0.003b	0.012b
C:N	0	24.4	122.8	61.0	29.1b	122.8	38.9a	30.3a	106.5	81.9	39.3	90.5	67.9
	0.2	24.4	118.0	64.0	32.1a	118.0	34.6b	27.3b	96.2	71.6	40.8	100.6	70.6
	0.4	25.3	117.5	64.2	31.3a	117.5	38.8a	35.0a	103.4	62.9	37.9	94.9	71.4
N:P	0	24.4	6.1	43.3	30.3	6.1	18.5	53.2	7.4	10.1	21.8	13.5	19.0
	0.2	44.3	21.0	15.1	35.5	21.0	22.7	37.2	8.2	8.7	28.5	13.1	28.7
	0.4	31.8	7.5	11.1	47.6	7.5	17.6	83.2	8.8	20.4	18.5	9.8	68.4
Lower case letters denote significant differences in elements for three intensities of Si supply, presented by bold (P < 0.05).

In our study, there were different responses in C:N:P stoichiometry to Si supply level among the four study species. For example, we found that Si treatments increased the foliar C:N stoichiometry in the seedlings of P. bournei (F_{2, 19} = 5.457, P = 0.013) and S. superba (F_{2, 18} = 8.999, P = 0.002) through altering their concentration of C and N, but did not affect the C:N or N:P stoichiometry of C. lanceolata and P. pubescens (Table 1).

4.1 Si supply increased the biomass of bamboo, but decreased the biomass of tree saplings

We demonstrated that experimentally manipulating the supply of Si to soil significantly enhanced the growth and development of P. pubescens, but decreased the biomass of P. bournei and S. superba (Fig. 2), which supports H₁ and is consist with other studies (Schaller et al. 2012a, Song et al. 2014a, Song et al. 2014b). For example, some studies found that Si promoted the growth and biomass of high Si-accumulating Poaceae through increasing the plants’ root-to-canopy ratio (Chen et al. 2002, Bukhari et al. 2015), as seen in P. australis and T. aestivum. Liu et al. (2011) found that Si promoted aboveground biomass by increasing plant height growth and its branching ability. In addition, a meta-analysis showed that Si supply increased the dry weight of stressed plants, but high Si-accumulating Poaceae plants did not show a stronger response than other families, contrary to expectations (Cooke and Leishman 2016). Indeed, Si was acquired as a nutrient through specific Si transporters in their roots, which contributed to alleviation of the impacts of biotic and abiotic stresses, increasing the biomass and production of Si-accumulating plants particularly (Ma and Yamaji 2006). However, we demonstrated reduced biomass production at the high Si supply levels for other tree seedlings (Fig. 2), which was in contrast to what we observed for bamboo seedlings. These results suggest that a stress response and imperfect regulation of Si uptake and transport occurs in tree seedlings, because they lack specific Si transporters in roots (Schaller et al. 2012a).

4.2 Moderate Si supply improved photosynthetic gas exchange properties

We found that moderate Si concentration improved the net photosynthetic rate of P. pubescens, but excess Si supply reduced its photosynthetic rate (Fig. 3), which supports H₂ and is consistent with other studies that examined other Si-accumulating plants. For example, some studies suggested that Si decreased the angle between the stem and plant leaves, thereby increasing light transmittance and improving its photosynthetic efficiency (Liang et al. 2006). In addition, Si is known to increase the biosynthesis of photosynthetic pigments, such as chlorophylls and carotenoids (Maghsoudi et al. 2015, Frazão et al. 2020).

Our results also showed that there were different photosynthetic responses to Si supply in other tree seedlings. For example, we observed decreased net photosynthetic rate in P. bournei at varying Si supply levels, and no significant response in C. lanceolata to Si supply (Fig. 3), which was probably attributed to different mechanisms of Si uptake and transport under these conditions (Liang et al. 2006, Frick et al. 2020). Indeed, there were differences in Si tissue content between bamboo and other tree seedlings; we found that the Si concentration of bamboo was much higher than that of other tree seedlings, regardless of what tissue type (i.e., leaf, stem, or root) was examined (Table 1). This suggests that bamboo can take up dissolved silicic acid [Si(OH)₄] from soil both actively and passively, unlike the passive mechanisms of Si uptake, where are determined by transpiration, seen in tree seedlings.

4.3 Si supply modified the C:N:P stoichiometry in plant

Generally, H₂SiO₃ supply increases Si availability in soil, but in our study there was no significant difference in the concentration of soluble Si (Si_SOL) in pot soil among Si supply levels (Figure S1), likely because amorphous Si was easily transformed to soluble Si (Yang et al. 2020) and we couldn’t determine Si availability from only the Si_SOL concentration (Sommer et al. 2013, Yang et al. 2018). We also found that high Si addition increased the foliar Si concentration of bamboo, whereas no significant difference in the Si concentration of other tree saplings among three intensities of Si supply. We suspected that this is because their different mechanisms of Si uptake and transport. The structural role played by Si is related to its incorporation into cell walls, such as phytoliths, which contribute to defense against herbivores and pathogens (Ma and Yamaji 2006, Mandlik et al. 2020).

Interestingly, we found that C concentrations in aboveground tissues declined with increasing Si supply, particularly in P. pubescens, a pattern seen in other species, such as rice, wheat, and sugarcane (Schaller et al. 2012b), whereas similar effects on N and P concentrations in plant tissues were not clearly apparent (Table 1). The observed decreases in C concentrations at varying Si supply levels might be due to a partial substitution of organic C with Si in aboveground tissues of P. pubescens (Schaller et al. 2012a, Katz et al. 2021). This would be advantageous for the plant because Si deposits, including phytholiths, are energetically cheaper to form and can confer similar defenses to alleviate biotic or abiotic stress for plants (Jonas et al. 2010, Schoelynck et al. 2010). This suggests that the observed decline in C concentration might reflect a switch of P. pubescens to an inexpensive defense mechanism when sufficient Si is available in the environment. Thus, we suspect that there were more competition advantages in bamboo due to Si defense than other trees during bamboo expansion.

Generally, leaf N and P content can be altered by the photosynthetic capacity of plants (LI et al. 2018, Zhang et al. 2018). Moreover, previous studies suggested that Si supply altered P metabolism and plant nutrient status in some high Si-accumulating Poaceae (Soratto et al. 2019, Katz et al. 2021). However, we found that there was no significant difference in the concentration of N and P of P. pubescens and C. lanceolata among three Si supply treatments, which was different from the N performance of P. bournei and S. superba. Si addition increased the foliar C:N stoichiometry of P. bournei and S. superba through altering their concentration of C and N, but did not affect the C:N or N:P stoichiometry of C. lanceolata and P. pubescens. We speculated that high Si ambient environment could not regulate nutrient status and disrupt balance in some tree saplings, except high Si-accumulating bamboo (Schaller et al. 2017). It has been reported that some tree saplings N and P availability are unlikely to be affected by Si supply (Ma and Takahashi 1991), and the phosphate uptake and distribution in plants is under genetic control (Bucher 2007), whereas uptake of Si is either unspecific or mediated by special groups of aquaporins, with subsequent genetic control (Ma et al. 2006, Ma and Yamaji 2006, Schaller et al. 2012b).

While not an essential element for plant growth, Si is indispensable for high Si-accumulating Poaceae, such as bamboo. Si supply increased Si concentration of bamboo, improved its production of aboveground tissues, and decreased C content. However, there was no significant difference in biomass or photosynthetic gas exchange properties among varying Si supply treatments for other tree seedlings. This indicates that Si exerts either a positive or negative effect on plants, depending on its species and the supply level of Si in the environment. Collectively, our findings provide experimental data to assess the different responses of bamboo and other trees on the growth, photosynthesis, and nutrient status under varying Si supply levels. These results could indicate that the different performance between bamboo and other trees is due to altering the Si availability in the ecosystem during bamboo expansion. We should quantify the growth of above and belowground biomass under varying Si supply levels in future studies to assess the shift in Si availability during bamboo expansion.

Acknowledgements

This research was supported by the 1000 Talents Plan award of Jiangxi province (江西省千人计划, jxsq2020101079), the National Natural Science Foundation of China (42067050, 41807028, 32060319), a grant from Education Department of Jiangxi Province (GJJ170242), and the National Biodiversity Field Monitoring Demonstration Base Renovation Program of the Ministry of Finance and Ministry of Environmental Protection (9131205274).

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Differential response of growth and C:N:P stoichiometry to Si supply between bamboo and other tree seedlings

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Abstract

Figures

Highlights

Introduction

Materials And Methods

2.1 Plant material, growth conditions, and experimental design

2.2 Measurement of Growth Traits

2.3 Photosynthetic gas exchange measurements

2.4 Soil samplings

2.5 Si concentrations

2.6 C, N and P concentration

2.7 Statistical analysis

Results

3.1 Impact of silicon supply on growth traits

3.2 Impact of silicon supply on photosynthetic gas exchange properties

3.3 Impact of Silicon supply on C:N stoichiometry in plants

Discussion

4.1 Si supply increased the biomass of bamboo, but decreased the biomass of tree saplings

4.2 Moderate Si supply improved photosynthetic gas exchange properties

4.3 Si supply modified the C:N:P stoichiometry in plant

Conclusion

Declarations

Acknowledgements

References

Supplementary Files

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