The plant hydraulic continuum from root to leaf: avoidance of catastrophic xylem failure under dynamic conditions

植物的生长和生存最终受到叶片水分供应的制约。即使在充足的水分供应下，光合作用也受到叶片气孔和水分在植物体内流动效率的限制。如果叶片气孔的失水与供水量的变化不能紧密协调，植物的导水系统（木质部）就会产生较大的负压（张力），导致气泡进入，最终导致灾难性的水力破坏和植物死亡。气泡是灾难性的，因为气泡会破坏水柱，导致木质部的那一部分失去功能。很少有研究考虑到植物组织中储存的水分被释放成蒸腾蒸汽，缓冲木质部张力波动的动态条件。本研究的总体目标是阐明植物从根到叶的水力通路的动态和静态特性在避免水力破坏中的相对作用。研究人员假设，水力安全的实现依赖于不同的机制：储水能力低的物种和植物器官主要依靠木质部的结构特征来避免运输失败，而储水能力高的物种和器官由于储水的短暂释放而避免运输失败。全面了解植物如何对它们每天所经历的动态压力作出反应，对于确定它们在当前和未来气候条件下应对水分供应变化的机制至关重要。由于水通常是植物生长最重要的限制因素之一，因此研究结果将对农业、林业和因土地利用、气候变化和其他因素变化而经历湿度变化的生态系统管理产生广泛影响。该项目涉及培养2名博士后、1名硕士生和数名本科生。该项目将涉及宾夕法尼亚州立大学、AgroParisTech（法国）和巴拿马的研究生和本科生。

Plant growth and survival are ultimately constrained by the supply of water to leaves. Even under adequate moisture supply, photosynthesis is restricted by the stomatal pores in leaves as well as the efficiency of water movement through the plant. If the stomatal pores in leaves do not tightly coordinate water loss with changes in water supply, large negative pressures (tension) will develop in the plant's water conducting system (xylem), causing entry of air bubbles and ultimately catastrophic hydraulic failure and plant death. Air bubbles are catastrophic because a bubble will break the water column and cause that part of the xylem to be nonfunctional. Few studies have considered dynamic conditions under which water stored in plant tissues is released into the transpiration steam, buffering fluctuations in xylem tension. The overall objective of this research is to elucidate the relative roles of both dynamic and static properties of the plant hydraulic pathway from root to leaf in avoiding hydraulic failure. The researchers hypothesize that there is a continuum of relative reliance on different mechanisms conferring hydraulic safety: species and plant organs with low water storage capacity rely primarily on xylem structural features to avoid transport failure, whereas species and organs with higher water storage capacity avoid transport failure due to a transient release of stored water. A comprehensive understanding of how plants react to the dynamic stresses they experience on a daily basis is critical for identifying mechanisms allowing them to cope with variation in moisture supply under current and future climate regimes. Because water is typically one of the most important limiting factors to plant growth, the results will have broad implications for agriculture, forestry and management of ecosystems experiencing altered moisture regimes as a result of changes in land-use, climate change and other factors. The project involves training of two postdoctoral scholars, one masters student, and several undergraduate students. The project will involve both graduate and undergraduate students from Penn State University, AgroParisTech (France) and Panama.