Phylogeny overrides environmental effects in explaining leaf and root nutrient concentrations in Fabaceae

Abstract

Plant nutrient concentrations are key to plant function, distribution and ecosystem processes. Understanding their phylogenetic and environmental controls is vital for predicting plant responses to global change. Fabaceae is one of the most ecologically and economically important plant families, yet how phylogeny and environment shape leaf and root nutrient concentrations remains unclear at broad spatial scales. We measured six nutrient concentrations (N, P, S, K, Ca and Mg) in both the leaves and roots of 121 Fabaceae species across various vegetation types in China. Standardized major axis regression was used to assess nutrient allocation strategies between leaves and roots, and Bayesian phylogenetic mixed‐effects models were applied to quantify the relative influences of phylogeny and environmental factors on nutrient concentrations. We found that S, K and Mg exhibited isometric scaling between leaves and roots, whereas N and P accumulated more slowly in leaves, and Ca more slowly in roots. According to the stable nutrient content hypothesis, elements critical for plant function tend to have more tightly regulated and stable concentrations. In line with this, the stability of N and P in leaves likely reflects their essential roles in photosynthesis, while the stable concentration of Ca in roots may be related to its role in supporting mycorrhizal symbiosis. For most nutrients, phylogeny accounted for a greater proportion of the variance in nutrient concentrations than environmental factors. However, environmental variables accounted for more variance in leaf P and K than phylogeny, with mean annual temperature being the strongest environmental predictor for both. This suggests that these two nutrients may play a particularly important role in the environmental adaptation of Fabaceae species. Synthesis. By elucidating leaf and root nutrient allocation patterns and quantifying the effects of phylogeny and environmental factors on nutrient concentrations, our findings advance understanding of plant adaptive strategies and can improve the capacity of biogeochemical models to simulate nutrient‐driven ecosystem processes.