Seminarios IHSM La Mayora - Michele Holbrook (Harvard University)

Hydromechanical forces in transpiring leaves: how the reversible collapse of minor vein xylem conduits protects against cavitation Vascular plants transport water in a metastable state and thus their lifeline to the soil operates at risk of cavitation. Understanding how this risk constrains plant productivity is central for models of plant and ecosystem function. Here I review work on cavitation thresholds and discuss the time scale of stomatal closure and xylem cavitation during drought, as well as the fate of embolised organs. I will also discuss a new hypothesis for how leaves protect their xylem from cavitation in the face of environmentally-driven fluctuations in transpiration rate. Using new tools, we have shown that the reversible collapse of the xylem conduits of the smallest vein orders protects upstream xylem conduits from cavitation associated with transient increases in transpiration. Overall, my goal is to illuminate what happens inside a transpiring leaf and to connect this massive movement of water and energy to the functioning of plants at larger scales.