Geographic patterns of leaf functional traits and environmental drivers of national key protected wild plant Davidia involucrata Baillon

The geographical patterns of plant functional traits and their environmental drivers remain central questions in plant population ecology. Leaf functional traits can directly affect the physiological and biochemical processes of plants, reflecting resource acquisition strategies and adaptation mechanisms. In this paper, we measured 17 functional traits of 18 populations of the national key protected wild plant Davidia involucrata Baillon across its natural distribution range in China, and analyzed the geographical patterns of leaf functional traits and their adaptation mechanisms to heterogeneous environments. At the local scale, the coefficients of variation of leaf traits ranged from 1.48% to 24.81%. The variation degree in the leaf carbon phosphorus ratio was the largest, while the variation degree of leaf organic carbon content was the smallest. With increasing longitude and latitude, leaf area, thickness, and serration number decreased significantly. With increasing altitude, leaf thickness, dry matter content, area, and phosphorus content increased significantly, while leaf shape became wider and rounder. Leaf serration enhanced the adaptability of D. involucrata leaves to cold. Significant leaf trait-geography correlations were mediated by climatic and/or soil factors. Environmental factors explained 79.90% of the variation in D. involucrata leaf traits, with variation of leaf traits mainly driven by geographical variables, climatic factors, and soil factors. Annual precipitation and soil nitrogen content were the strongest explanatory factors for leaf trait variation, with increasing precipitation or decreasing soil nitrogen leading to smaller and thinner leaves. In general, the functional traits of D. involucrata leaves showed a clear pattern at the species distribution scale, with precipitation and soil nitrogen content playing an important role in the formation of geographical patterns.