Environmental constraints on the inter-genus variation in the scaling relationship between leaf nitrogen and phosphorus concentrations

Aims The scaling relationship between nitrogen (N) and phosphorus (P) concentrations ([N] and [P], respectively) in leaves manifests plants’ relative investment between the two nutrients. However, the variation in this relationship among taxa as well as its causes was seldom described. Methods The analysis was based on a dataset including 2483 leaf samples from 46 genera of angiosperm woody plants from 1733 sites across China. We calculated the leaf N–P scaling exponent (βL) with an allometric equation ([N] = α[P]β), for each genus, respectively. We then performed phylogenetic path analyses to test how the climate and soil niche conditions of these genera contributed to the inter-genus variation in βL. Important Findings The genera living with lower soil P availability presented a more favoured P uptake relative to N, as shown by the higher βL, suggesting a resistant trend to P limitation. Additionally, genus-wise βL was positively correlated with soil N–P scaling exponents (βS), implying that the variation in leaf nutrients is constrained by the variability in their sources from soil. Finally, climatic factors including temperature and moisture did not affect βL directly, but could have an indirect influence by mediating soil nutrients. Phylogeny did not affect the inter-genus variation in βL along environmental gradients. These results reveal that the trade-off between N and P uptake is remarkably shaped by genus niches, especially soil nutrient conditions, suggesting that the βL could be considered as a functional trait reflecting characteristics of nutrient utilization of plant taxa in response to niche differentiation.