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

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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.