Key hydraulic traits control the dynamics of plant dehydration in four contrasting tree species during drought.

Trees are at risk of mortality during extreme drought, yet our understanding of the traits that govern the timing of drought-induced hydraulic failure remains limited. To address this, we tested SurEau, a trait-based soil-plant-atmosphere model designed to predict the dynamics of plant dehydration as represented by changes in water potential, against those observed in potted trees of four contrasting species (Pinus halepensis, Populus nigra, Quercus ilex, and Cedrus atlantica) exposed to drought. SurEau was parameterised with a range of plant hydraulic and allometric traits, soil, and climatic variables. We found close correspondence between predicted and observed plant water potential (MPa) dynamics during early phase drought leading to stomatal closure, as well as during latter phase drought leading to hydraulic failure in all four species. A global model's sensitivity analysis revealed that for a common plant size (leaf area) and soil volume, dehydration times from full hydration to stomatal closure (Tclose) was most strongly controlled by leaf osmotic potential (Pi0) and its influence on stomatal closure, in all four species, while maximum stomatal conductance (gsmax) also contributed to Tclose in Q. ilex and C. atlantica. Dehydration times from stomatal closure to hydraulic failure (Tcav) was most strongly controlled by Pi0, the branch residual conductance (gres), and Q10a sensitivity of gres in the three evergreen species, while xylem embolism resistance (P50) was most influential in the deciduous species Populus nigra. Our findings point to SurEau as a highly useful model for predicting changes in plant water status during drought and suggest adjustments made in key hydraulic traits are potentially beneficial to delaying the onset of drought-induced hydraulic failure in trees.