Abstract: The aim of this study was to clarify the biogeographic patterns of leaf functional traits of Bauhinia brachycarpa, mainly vein density, and the influencing mechanisms. We investigated the variation characteristics of vein density in different grades and leaf morphology of Bauhinia brachycarpa, a dominant shrub along a latitude gradient (23°16′N-31°30′N, 101°28′E-103°25′E) in the arid valley of southwest China, and analyzed the relationship among leaf traits. The results showed that vein density and leaf surface area decreased with increasing latitude, and that main vein density was negatively correlated with specific leaf area. The total vein density and minor vein density were independent of leaf morphological traits, such as leaf surface area, while the main vein diameter was positively correlated with leaf morphological traits and specific leaf area. The latitudinal variation of leaf vein traits was affected by the average precipitation in dry season, soil cation exchange capacity, altitude, and annual average temperature. Our results help reveal the ecological adaptation mechanism of xerophytes in arid valleys.

Key words: vein density, leaf surface area, arid valley, latitude gradient