We compared branch and leaf functional traits of Ulmus pumila trees inhabiting different climatic zones (sub-humid, dry sub-humid and semi-arid zones), aiming to investigate the role of trait plasticity and coordination in tree acclimation to different water conditions. The results showed that leaf drought stress of U. pumila increased significantly from sub-humid to semi-arid climatic zones, as indicated by a 66.5% reduction in leaf midday water potential. In the sub-humid zone with less severe drought stress, U. pumila had higher stomatal density, thinner leaves, larger average vessel diameter, pit aperture area and membrane area, which could ensure the higher potential water acquisition. With the increases of drought stress in dry sub-humid and semi-arid zones, leaf mass per area and tissue density increased, and the pit aperture area and membrane area decreased, indicating stronger drought tolerance. Across different climatic zones, the vessel and pit structural characteristics were strongly coordinated, while a trade-off between xylem theoretical hydraulic conductivity and safety index was found. The plastic adjustment and coordinated variation of anatomical, structural and physiological traits may be an important mechanism contributing to the success of U. pumila in different climate zones with contrasting water environments.
以亚湿润区、干旱亚湿润区和半干旱区的白榆个体为对象,研究了枝叶功能性状的可塑性及协同变异。结果表明: 从亚湿润区到半干旱区,白榆叶片受到的干旱胁迫显著增加,正午水势降低了66.5%。在干旱胁迫较轻的亚湿润区,白榆的气孔密度较高,叶片较薄,平均导管直径、纹孔开口面积和纹孔膜面积较大,保证了其较高的潜在水分获取能力。在干旱亚湿润区和半干旱区,随着干旱胁迫的增强,白榆比叶重和叶片组织密度提高,纹孔开口面积和纹孔膜面积缩小,其耐旱能力增强。导管与纹孔结构特征的变异存在协同性,而木质部理论导水率与安全性指数之间则表现出权衡关系。枝叶解剖、形态和生理性状的可塑性调整与协同变异是白榆能够成功适应不同水分环境的重要机制。.
Keywords: functional trait; hydraulic architecture; intraspecific variation; water availability; water use strategy.