Abstract: Objective This study investigates the variation in functional traits of Sophora japonica across a precipitation gradient and the climatic drivers underlying this variation, aiming to elucidate its habitat adaptation strategies.Method Ten study sites were selected along the precipitation gradient from the humid zone in southeastern China to the arid zone in northwestern China, and a conspecific populations of S. japonica was used to measure functional traits, including leaf functional traits (stomatal size, stomatal density, vein density, huber value, specific leaf mass, leaf thickness, palisade tissue thickness, spongy tissue thickness, palisade to spongy tissue ratio) and branch functional traits (vessel diameter, vessel density, vessel wall thicknesses, thickness span ratio, wood density). Quantify relationships between climatic factors (mean growing-season temperature, sunshine duration, and mean annual precipitation) and functional trait variation in S. japonica, reveal coupling patterns among traits, and elucidate its habitat adaptation strategies.Result Among the functional traits of S. japonica, the three traits with the higher coefficients of variation were palisade tissue thickness (37.26%), palisade to spongy tissue ratio (32.51%), and vessel density (27.53%), while the three traits with the lower coefficients of variation were vessel diameter (12.07%), wood density (13.32%), and vein density (14.75%). Mean annual precipitation exhibited significant correlations with functional trait variation in S. japonica branches (P<0.05), whereas no significant associations were detected between either mean growing-season temperature or sunshine duration and these trait variations. Specific leaf mass of S. japonica showed a significantly positive correlation with both leaf thickness and palisade tissue thickness (P<0.05), while vessel diameter exhibited a highly and significant negative correlation with vessel density (P<0.01).Conclusion Trait variation and inter-trait coupling reflect the habitat adaptation strategies of S. japonica: the overall variability in leaf functional traits exceeds that of branch functional traits. Among climatic factors, mean annual precipitation had the greatest influence on the variation in functional traits of S. japonica, primarily affecting the variation in its branch functional traits. Compared to S. japonica in humid regions, those in semi-arid/arid regions adapt by developing leaf thickness to enhance water storage capacity and enlarging vessel diameter to improve hydraulic efficiency, thereby optimizing short-term water utilization. In semi arid/arid regions, S. japonica achieves efficient utilization of precipitation pulses and rapid growth through the coordinated functioning of its leaf and branch traits.

Key words: climate change, adaptation strategies, trait variation, plant functional trait, Sophora japonica