Elevational patterns and thresholds of plant functional traits across China's biomes

Elevational gradients integrate coordinated variation in temperature, water availability, and soil conditions, providing a natural experiment for examining large-scale trait–environment relationships. Using a nationwide dataset of 20,774 vascular plant species across China, we quantified elevational patterns in leaf area, plant height, seed size, and cone size, evaluated environmental drivers, and explored potential responses under future climate scenarios. All four traits exhibited significant nonlinear relationships with elevation, with statistically supported breakpoints at approximately 1838 m (leaf area), 2925 m (plant height), 2585 m (seed size), and 2275 m (cone size). Beyond these breakpoints, vegetative traits showed steeper negative scaling with elevation, whereas reproductive traits varied more gradually, suggesting differential sensitivity to high-elevation constraints. Structural equation modeling indicated that trait–environment coupling differed between elevation zones: indirect environmental mediation was more pronounced at low elevations, while direct elevation effects became relatively stronger at high elevations. Scenario-based projections derived from core climatic drivers suggested that vegetative traits may exhibit greater sensitivity to future hydrothermal changes than reproductive traits. Together, these findings highlight elevation-dependent shifts in trait–environment relationships and emphasize trait-specific sensitivities across heterogeneous landscapes. • Nationwide synthesis of four key functional traits across 20,774 vascular plant species in China. • Integrated threshold detection, machine learning, and SEM reveal divergent elevational sensitivities between vegetative and reproductive traits. • Elevation-dependent climate–trait coupling enables scenario-based projections of trait sensitivity under future climates.