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

Abstract

The 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 (Ψ 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 Ψ 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 ~Ψstem ), demonstrating that grapevines become increasingly tolerant to low Ψ stem as the season progresses in coordination with the decrease in Ψ TLP . We also used the SurEau hydraulic model to demonstrate a direct link between osmotic adjustment and the plasticity of g s ~Ψstem . To understand the possible advantages of g s ~Ψstem 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 ~Ψstem . These findings show that accounting for dynamic stomatal regulation is critical for understanding drought tolerance.

Do hourly and seasonal changes in non-structural carbohydrates in grapevine leaves contribute to osmotic adjustment and regulation of photosynthesis?

“…In agreement with past studies of grapevines, we observed an increase in foliar osmotic concentration in response to water deficit (Patakaset al , 2002;Hochberg et al , 2017) and as the seasonal progressed (Alsina et al , 2007;Sorek et al , 2021;Herrera et al , 2022). However, SC did not play a major role in these adjustments.…”

Seasonal adjustment of leaf embolism resistance and its importance for hydraulic safety in deciduous trees

“…Such is the case of the turgor loss point (Ψ TLP ). Since Ψ TLP is coupled to stomatal closure (Brodribb et al, 2003 ), its adjustment to a lower Ψ x (a.k.a., osmotic adjustment) along the season (Bartlett et al, 2014 ; Herrera et al, 2022 ) allows plants to maintain transpiration in the face of declining Ψ x as the summer intensifies (Kozlowski & Pallardy, 2002 ). Adjusting the threshold of stomatal closure without changing the P 12 or P 50 seems unreasonable, as it would increase the risk of hydraulic failure and leaf death.…”

Physiological and Molecular Aspects of Two Thymus Species Differently Sensitive to Drought Stress

“…RWC is a factor that assesses both the effect of the soil−plant−atmosphere water continuum and the effect of membrane osmotic potentials. Indeed, different cultivars (but plants of the same species) with the same foliar water potential can have different RWCs [6]. RWC decreases proportionally with the decrease in water availability [7].…”