Leaf Trait Differentiations Depend on Plant Size in a Modular Assembled Community of Evergreen and Deciduous Trees From a Degraded Karst Forest Ecosystem.

Generally, a forest community can be viewed as functionally integrated assemblages composed of modular subcommunities representing different functional groups, such as evergreen and deciduous plants, which exhibit distinct trait strategies along the leaf economics spectrum. However, how plant size drives leaf trait differentiation between evergreen and deciduous subcommunities remains unclear. In this study, we surveyed 53 forest plots in a typical subtropical karst forest and measured leaf traits, including specific leaf area (SLA), leaf tissue density (LTD), leaf dry matter content (LDMC), and leaf carbon (LCC), nitrogen (LNC), and phosphorus (LPC) contents, as well as soil physicochemical properties. All woody species were classified into evergreen and deciduous subcommunities based on leaf habit. Relationships among plant size, leaf traits, and soil variables were analyzed using linear regression, principal component analysis, and multiple regression. The results showed that the deciduous subcommunity exhibited significantly greater tree DBH, height, SLA, LDMC, LNC, LPC, and leaf N/P ratio, but lower LCC, C/N, and C/P than the evergreen subcommunity, indicating clear differentiation in leaf trait strategies between the two subcommunities. Additionally, distinct trait responses to increasing plant size in both subcommunities, particularly for SLA, LNC, and C/N, suggest plant size-dependent trait differentiation. Moreover, the relative effects indicated that evergreen leaf traits were mainly influenced by soil total phosphorus and habitat heterogeneity, whereas deciduous leaf traits were primarily driven by plant size. Overall, our findings demonstrate that modular subcommunities exhibit distinct leaf trait characteristics and resource-use strategies, with an acquisitive strategy in the deciduous subcommunity and a conservative strategy in the evergreen subcommunity, both closely associated with plant size in degraded karst forests. These results provide new insights into trait-based community assembly by highlighting size-dependent differentiation in modular subcommunities, with implications for understanding vegetation functional evolution and informing ecological restoration of degraded karst forest ecosystems.