| Abstract: | - Based on the elemental composition of major biochemical molecules associated with different biological functions, the ‘growth rate hypothesis’ proposed that organisms with a higher growth rate would be coupled to lower C:N, especially lower C:P and N:P ratios. However, the applicability of the growth rate hypothesis for plants is unclear, especially for shrubs growing under different water supply.
- We performed an experiment with eight soil moisture levels (soil water content: 4%, 6%, 8%, 13%, 18%, 23%, 26% and 28%) to evaluate the effects of water availability on leaf C:N:P stoichiometry in the shrub Zygophyllum xanthoxylum.
- We found that leaves grew slowly and favored accumulation of P over C and N under both high and low water supply. Thus, leaf C:P and N:P ratios were unimodally related to soil water content, in parallel with individual leaf area and mass. As a result, there were significant positive correlations between leaf C:P and N:P with leaf growth (u).
- Our result that slower‐growing leaves had lower C:P and N:P ratios does not support the growth rate hypothesis, which predicted a negative association of N:P ratio with growth rate, but it is consistent with recent theoretical derivations of growth–stoichiometry relations in plants, where N:P ratio is predicted to increase with increasing growth for very low growth rates, suggesting leaf growth limitation by C and N rather than P for drought and water saturation.
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