Tracking and quantifying the dynamics of tree water storage under future climate change (CapaciTree)

forthcoming

Climate change threatens the future of forest functioning, compromises their productivity, increases the risk of fire or insect outbreaks, and ultimately causes tree mortality. Under drought, trees can experience catastrophic hydraulic failure due to xylem cavitation (i.e. the breakage of the water column), which is the main cause of tree mortality worldwide. Trees can partially avoid cavitation by mobilising water stored in their tissues into the xylem conduits to meet the atmospheric evaporative demand, a process known as hydraulic capacitance. Despite the relevance of capacitance for predicting transpiration and mortality risk under climate change, we still lack empirical evidence for the dynamics of storage-use and refilling of plant-water pools under drought, particularly for trees growing under natural conditions. Here, I propose to combine labelling experiments with isotopically enriched water with a new technique to selectively extract water from different woody tissues, to quantify and characterize hydraulic capacitance, specifically the refilling and storage-use dynamics, and its contribution to transpiration. I will: 1) characterize the dynamics of tree storage water in relation to tree size; 2) develop a novel methodology to quantify the contribution of capacitance to transpiration; 3) estimate the contribution of tree capacitance to transpiration in mature trees in a native Mediterranean forest subjected to severe drought; and 4) compare the proposed methodology with conventional techniques to assess capacitance in three coexisting Mediterranean tree species in response to drought. My expertise in plant ecophysiology will be key to undertake this project, which will also leverage my skillset for the study of forest resilience to drought. This project will serve to build more realistic models of forest responses to drought and to inform forest management policies to adapt forest ecosystems to climate change.