Résumé
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 accumulation
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. Aboveground 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 characterize 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.