Sand-fixing shrub Salix gordejevii plays an important role in sand dune stabilization but often shows severe decline and mortality on the windward slopes of active dunes. The objective of this study was to explore the environmental drivers and physiological mechanisms behind its decline and mortality on the windward slopes of active sand dunes. The xylem hydraulics, sap flow, water relations and non-structural carbohydrate reserves were measured for S. gordejevii plants that respectively inhabited interdune, leeward and windward positions of active dunes with contrasting soil water regimes. Root exposure caused by wind erosion, rather than low soil moisture, predisposed windward S. gordejevii plants to stronger water stress. Correspondingly, the windward plants showed reduced transpirational water use and exhibited a suite of acclimative adjustments in leaf traits favoring water conservation. Despite these adjustments, windward S. gordejevii plants still suffered from higher risks of hydraulic failure and branch mortality. No evidence of carbon depletion in windward S. gordejevii plants was found although the soluble sugar to starch ratios changed significantly. Our findings suggest that wind-erosion-induced root exposure triggers water stress and eventually causes the mortality of windward S. gordejevii plants, during which increased risk of hydraulic dysfunction is pronounced.

中文翻译：

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由于根部暴露引发的水分胁迫引起的水力功能障碍是导致活动沙丘迎风坡上的 Salix gordejevii 灌木死亡的原因

固沙灌木 Salix gordejevii 在沙丘稳定中起着重要作用，但在活动沙丘的迎风坡上经常表现出严重的衰退和死亡。本研究的目的是探索活动沙丘迎风坡上其衰退和死亡率背后的环境驱动因素和生理机制。测量了分别居住在活动沙丘的沙丘间、背风和迎风位置的 S. gordejevii 植物的木质部水力学、树液流、水分关系和非结构性碳水化合物储备，并具有对比的土壤水分状况。风蚀引起的根系暴露，而不是低土壤湿度，使迎风的 S. gordejevii 植物更容易受到水分胁迫。相应地，迎风植物的蒸腾耗水量减少，并在叶片性状方面表现出一系列有利于节约用水的适应性调整。尽管进行了这些调整，迎风 S. gordejevii 植物仍然面临更高的水力故障和分支死亡风险。尽管可溶性糖与淀粉的比例发生了显着变化，但没有发现迎风 S. gordejevii 植物中碳耗竭的证据。我们的研究结果表明，风蚀引起的根系暴露会引发水分胁迫，并最终导致迎风 S. gordejevii 植物死亡，在此期间水力功能障碍的风险增加是明显的。尽管可溶性糖与淀粉的比例发生了显着变化，但没有发现迎风 S. gordejevii 植物中碳耗竭的证据。我们的研究结果表明，风蚀引起的根系暴露会引发水分胁迫，并最终导致迎风 S. gordejevii 植物死亡，在此期间水力功能障碍的风险增加是明显的。尽管可溶性糖与淀粉的比例发生了显着变化，但没有发现迎风 S. gordejevii 植物中碳耗竭的证据。我们的研究结果表明，风蚀引起的根系暴露会引发水分胁迫，并最终导致迎风 S. gordejevii 植物死亡，在此期间水力功能障碍的风险增加是明显的。