Regulation of leaf elemental composition in a subtropical river basin with diverse forest landscapes

Understanding the eco-evolutionary processes that govern leaf elemental composition in subtropical regions with diverse forest landscapes remains a challenge. Here, we investigated the phylogenetic and environmental regulation of leaf elemental composition in subtropical forests.

We sampled surface soils and leaves from herbs, ferns, deciduous woody species, and evergreen woody species across four forest landscapes (montane, valley, karst, and island forests) in the subtropical Lijiang River basin. We used phylogenetic comparative methods to identify regulators of leaf elemental composition.

Leaf elemental concentrations varied significantly among growth forms, with evergreen woody species presenting the highest leaf C concentration relative to N, P, and K. Apart from C, leaf elemental concentrations also showed significant variations across forest landscapes; for instance, karst forest species exhibited the highest leaf Ca and Mg concentrations but the lowest leaf P concentration, reflecting pronounced P deficiency and enhanced supply of Ca and Mg. Phylogenetic signal, indicating phylogenetic conservatism, was significantly detected in leaf C, K, Ca, and Mg concentrations. Evolutionary model comparisons suggested that stabilizing selection towards multiple optima for growth forms best explained variation in leaf C concentration, while stabilizing selection towards multiple optima for each growth form within a specific landscape emerged as the dominant process for leaf N, P, K, Ca, and Mg concentrations.

Our study highlights the critical roles of leaf elemental conservatism and stabilizing selection towards multiple optima for growth forms within and across forest landscapes in regulating leaf elemental composition in subtropical region.