A dynamical system perspective on plant hydraulic failure

Photosynthesis is governed by leaf water status that depends on the difference between the rates of transpiration and water supply from the soil and through the plant xylem. When transpiration increases compared to water supply, the leaf water potential reaches a more negative equilibrium, leading to water stress. Both high atmospheric vapor pressure deficit and low soil moisture increase the water demand while decreasing the supply due to lowered soil-to-root conductance and xylem cavitation. Therefore, dry conditions may eventually reduce the leaf water potential to the point of collapsing the plant hydraulic system. This "hydraulic failure" is shown to correspond to a fold bifurcation where the environmental parameters (vapor pressure deficit and soil moisture) trigger the loss of a physiologically sustainable equilibrium. Using a minimal plant hydraulic model, coordination among plant hydraulic traits is shown to result in increased resilience to environmental stresses, thereby impeding hydraulic failure unless hydraulic traits deteriorate due to prolonged water shortage or other damages.