Stomatal responses in grapevine become increasingly more tolerant to low water potentials throughout the growing season

International audienceThe leaf of a deciduous species completes its life cycle in a few months. During leaf maturation, osmolyte accumulation leads to a significant reduction of the turgor loss point (psi(TLP)), a known marker for stomatal closure. Here we exposed two grapevine cultivars to drought at three different times during the growing season to explore if the seasonal decrease in leaf psi(TLP) influences the stomatal response to drought. The results showed a significant seasonal shift in the response of stomatal conductance to stem water potential (g(s)similar to psi(stem)), demonstrating that grapevines become increasingly tolerant to low psi(stem) as the season progresses in coordination with the decrease in psi(TLP). We also used the SurEau hydraulic model to demonstrate a direct link between osmotic adjustment and the plasticity of g(s)similar to psi(stem). To understand the possible advantages of g(s)similar to psi(stem) plasticity, we incorporated a seasonally dynamic leaf osmotic potential into the model that simulated stomatal conductance under several water availabilities and climatic scenarios. The model demonstrated that a seasonally dynamic stomatal closure threshold results in trade-offs: it reduces the time to turgor loss under sustained long-term drought, but increases overall gas exchange particularly under seasonal shifts in temperature and stochastic water availability. A projected hotter future is expected to lower the increase in gas exchange that plants gain from the seasonal shift in g(s)similar to psi(stem). These findings show that accounting for dynamic stomatal regulation is critical for understanding drought tolerance