Nitrogen availability and plant-plant interactions drive leaf silicon concentration in wheat genotypes

Abstract

Estimating plasticity of leaf silicon (Si) in response to abiotic and biotic factors underpins our comprehension of plant defences and stress resistance in natural and agroecosystems. However, how nitrogen (N) addition and intraspecific plant-plant interactions affect Si concentration remains unclear.We grew 19 durum wheat genotypes (Triticum turgidum ssp. durum) in pots, either alone or in intra- or intergenotypic cultures of two individuals, and with or without N. Above-ground biomass, plant height and leaf [Si] were quantified at the beginning of the flowering stage.Nitrogen addition decreased leaf [Si] for most genotypes, proportionally to the biomass increase. Si plasticity to plant-plant interactions varied significantly among genotypes, with both increases and decreases in leaf [Si] when mixed with a neighbour, regardless of the mixture type (intra-/intergenotype). Besides, increased leaf [Si] in response to plant-plant interactions was associated with increased plant height.Our results suggest the occurrence of both facilitation and competition for Si uptake from the rhizosphere in wheat mixtures. Future research should identify which leaf and root traits characterise facilitating neighbours for Si acquisition. We also show that Si could be involved in height gain in response to intraspecific competition, possibly for increasing light capture. This important finding opens up new research directions on Si and plant-plant interactions in both natural ecosystems and agroecosystems. More generally, our results stress the need to explore leaf Si plasticity in responses to both abiotic and biotic factors to understand plant stress resistance. Read the free Plain Language Summary for this article on the Journal blog.

Keywords: agroecology; facilitation; genotype mixture; intraspecific variation; nutrient limitation; phenotypic plasticity; plant competition; plant height.

FIGURE 1

Leaf silicon concentrations ([Si]) of 19 durum wheat genotypes grown alone (single) and for two levels of N availability (means ± SE; n = 3) in (a). Boxplots showing the effects of plant growth modalities (single, intra‐ and intergenotypic culture) on leaf [Si] in (b), plant above‐ground biomass in (c) and plant height in (d), for each N treatment. In (a), data are ranked by increasing genotype‐mean leaf [Si] in the N⁻ treatment for both plots, and results of ANOVA (F‐values) conducted between the genotypes are given. In (b)–(d), the central horizontal bar in each box shows the median, the box represents the interquartile range (IQR) and the whiskers show the location of the most extreme data points that are still within a factor of 1.5 of the upper or lower quartiles. Each point indicates one individual, and the y‐axis for leaf [Si] in (b) is on a logarithmic scale to improve visualisation. Different letters indicate significant differences (p < 0.05) between single, intra‐ and intergenotypic culture within an N treatment. ***p < 0.001; **p < 0.01; *p < 0.05; ns, not significant.

FIGURE 2

Variation in log response ratios (logRR) of leaf silicon (Si) concentrations to nitrogen (N) fertilisation for the single plants in (a) and to plant–plant interactions for both N treatments in (b) among 19 wheat genotypes. Both intra‐ and intergenotypic culture were considered together in the analysis in (b) (see Figure S1 for separate analyses). Data are ranked by increasing genotype‐mean logRR. The central horizontal bar in each box shows the median, the box represents the interquartile range (IQR), the whiskers show the location of the most extreme data points that are still within a factor of 1.5 of the upper or lower quartiles, and black points are values that fall outside the whiskers. Results of ANOVA (F‐values) conducted between the genotypes are given. LogRR significantly different from zero following student t‐tests are indicated with stars. ***p < 0.001; **p < 0.01; *p < 0.05; ns, not significant.

FIGURE 3

Variation in log response ratios (logRR) of leaf silicon (Si) concentrations to intergenotypic culture for both N treatments as a function of neighbour identity. Data are ranked by increasing neighbour identity‐mean logRR for both plots. The central horizontal bar in each box shows the median, the box represents the interquartile range (IQR), the whiskers show the location of the most extreme data points that are still within a factor of 1.5 of the upper or lower quartiles, and black points are values that fall outside the whiskers. Results of ANOVA (F‐values) conducted between the neighbour identity are given. LogRR significantly different from zero following student t‐tests are indicated with stars for the N⁻ treatment. ***p < 0.001; **p < 0.01; *p < 0.05; ns, not significant.

FIGURE 4

Relationships between the log response ratio (logRR) of leaf silicon (Si) concentrations and those of biomass and height to nitrogen (N) fertilisation for the single in (a) and to plant–plant interactions for both N treatments in (b). Both intra‐ and intergenotypic culture were considered together as ‘plant–plant interactions’ in the analyses (see Figure S3 for separate analyses). Red lines indicate regression lines between variables, and multiple R‐squared are given. ***p < 0.001; **p < 0.01; *p < 0.05; ns, not significant.