Nonlinear biogeographic responses and threshold patterns in vegetative versus reproductive traits across China's...

Understanding how ecosystem productivity is associated with plant trait variation is essential for linking trait-based ecology with ecosystem functioning. However, whether vegetative and reproductive organ-size traits show different responses along broad productivity gradients remains unclear. Here, we compiled a nationwide dataset of 23,848 vascular plant taxon records across China to examine nonlinear responses of leaf area, plant height, seed size, and fruit/cone size to net primary productivity (NPP). We further assessed whether climatic, edaphic, vegetation, and nitrogen-deposition variables differed in their associations with these traits across productivity regimes. Vegetative organ-size traits showed clearer nonlinear associations with NPP than reproductive organ-size traits. Leaf area and plant height increased rapidly from low to intermediate productivity and then showed diminishing marginal increases at trait-specific breakpoints within 300-500 g C m^-2 yr^-1. By contrast, seed size and fruit/cone size showed weaker and more trait-specific responses, rather than remaining invariant across the gradient. Environmental associations also varied among traits and productivity regimes, indicating that productivity is linked to both organ-size trait variation and the environmental context underlying that variation. These findings clarify how productivity is associated with size-related trait variation, while highlighting the need to integrate leaf economic, floral, chemical, and physiological traits to fully understand plant functional strategies across heterogeneous ecosystems.