Significant Contribution of Evolutionary History in Coordinating Plant Size and Functional Traits in Understory Ferns...

The coordinated variation between plant size and functional traits is a critical link connecting individual ecological strategies and community assembly. However, unlike angiosperms, the drivers of trait-size coordination in coexisting fern species remain unclear. This study sampled seven coexisting fern species in a subtropical secondary forest, measuring biomass (an indicator of plant size) and functional traits related to leaf and root morphology and elemental composition. The coordinated relationship between plant individual size and functional traits was investigated using regression and principal component analysis, while the relative contributions of phylogeny, species identity, and individual biomass to trait variation were quantified via Bayesian phylogenetic generalized linear mixed models. Results indicated that there is a clear trait-size coordination relationship. Specifically, significant linear or nonlinear relationships were identified between plant size and multiple functional traits (e.g., elemental concentrations, specific leaf area, and specific root length), indicating a transition from "fast-acquisitive" to "conservative" strategies. However, variance partitioning indicated that phylogeny and species identity together explained the majority of variation in leaf and root traits (71.4% on average), whereas the independent contribution of individual biomass was minimal (7.1% on average). The results suggest that although significant trait-size coordination exists in understory fern communities, this coordination is statistically dominated by evolutionary history (phylogeny and species identity), though the ecological significance of plant size remains evident in significant trait-size coordination patterns. Overall, the coordinated variation between plant size and functional traits is pivotal in forging resource-allocation strategies and fostering fern species coexistence, highlighting that evolutionary background must be foregrounded when disentangling the mechanisms of functional community assembly.