Relationships between xylem morphology, stomatal responses and plant hydraulics, in three field grown grapevine varieties

Abstract

Grapevines are useful model plants for research on the physiology of water stress responses. Variable responses at the stomatal level have been described in different varieties with implications on the hydraulic conductance of the plant and eventually impacts on the tension imposed to the xylem architecture, depending on xylem properties. In order to assess possible associations between stomatal responses (gs) to evaporative demand (VPD), water potentials at the root to leaf gradient, plant hydraulics and xylem morphoanatomical traits, a two-season research study has been conducted in Cabernet Sauvignon (CS), Carmenere (C) and Syrah (S) in the field, under mild water stress (MWS) and well watered (WW) conditions. During the first season, significant differences between treatments were only observed on Ψ_STEM in all the varieties, neither for ΨPD nor for Ψ_leaf. Also, transpiration was clearly driven by VPD only in S, not in CS and C. On the other hand daily carbon assimilation and transpiration, and also the whole plant hydraulic conductance, were reduced along the season in CS and C, but maintained in S. When assessing xylem vulnerability to cavitation, during the second season on the same well-watered plants from previous experiments, S was the most resistant, followed by C and CS. However, S has a higher theoretical conductance per xylem area, and a higher proportion of xylem vessels of larger diameters than in CS and C, which, theoretically, are more prone to cavitation. It seems that in Mediterranean climates, even well watered plants tend to reduce the capacity for water transport with implications for the carbon gain in varieties with more vulnerable xylem to cavitation.