Legacy effects control root elemental composition and stoichiometry in subtropical forests: empirical support for the biogeochemical niche hypothesis

The biogeochemical niche (BN) hypothesis, where BN is defined as the species-specific occupation of an n-dimensional bio-element space, has been proposed as an approach to quantify ecological niches and explain community assembly. However, empirical studies of the BN hypothesis have tended to measure leaf chemical element content as a proxy for whole-plant element status, with little regard to other plant organs involved in biological processes, such as root nutrient uptake. Based on root concentrations and stoichiometry of 9 elements in 137 tree species of a subtropical forest, we test following hypotheses(1) each species with specific fine root elemental composition and stoichiometry from different taxonomic group occupy a specific position in the multidimensional space; (2) legacy effects (phylogenetic and species) primarily drive species-specific element use; and, (3) fine root elemental composition, stoichiometry and BNs of subtropical tree species are a product of legacy effects, type of mycorrhizal association, and local-scale variability in resources.