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

植物的生长和存活最终受到叶片水分供应的限制。即使在充足的水分供应下，光合作用也受到叶片中气孔的限制，以及水分在植物中流动的效率。如果叶片中的气孔不能紧密地协调水分损失与供水的变化，则植物的导水系统（木质部）中将产生大的负压（张力），导致气泡进入并最终导致灾难性的水力失效和植物死亡。气泡是灾难性的，因为气泡会破坏水柱，导致木质部的这一部分失去功能。很少有研究考虑动态条件下，储存在植物组织中的水被释放到蒸腾蒸汽，缓冲木质部张力的波动。本研究的总体目标是阐明从根到叶的植物水力途径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，有一个连续的相对依赖于不同的机制赋予水力安全：物种和植物器官具有低水存储能力主要依赖于木质部结构特征，以避免运输失败，而物种和器官具有较高的水存储能力避免运输失败，由于储存水的瞬时释放。全面了解植物如何对它们每天经历的动态压力做出反应，对于确定使它们能够科普当前和未来气候制度下水分供应变化的机制至关重要。由于水通常是植物生长的最重要限制因素之一，因此研究结果将对农业、林业和由于土地使用、气候变化和其他因素的变化而改变湿度状况的生态系统的管理产生广泛影响。该项目包括培养两名博士后学者，一名硕士生和几名本科生。该项目将涉及来自宾夕法尼亚州立大学、巴黎农业技术学院（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.