Consistency of the hydraulic traits and stomatal responses in grapevines with contrasting hydraulic vulnerability

Abstract

Context and purpose of the study ‐ Different from wild species in arid and semiarid conditions, cultivated species are very sensitive to drought and, beyond some stress thresholds, food production is not possible. It is therefore important to gain further knowledge on the responses of plant species of agricultural importance to realistic water shortage extents, and their consistencies. A valuable model for water stress studies has been the grapevine (Vitis vinifera L.), a species with a high variability in their stomatal sensitivity to water stress. In contrast to usual agricultural practices, grapevines for oenological purposes are grown under controlled water stress conditions.

Material and methods ‐ In the abovementioned context, we aimed to study the physiological responses to a progressive, not severe (Ѱpd > ‐1MPa), water deficit in the grapevine varieties Syrah and Carménère, in two consecutive season using different sites each year, and with different row orientation. We assessed a) the relationship between the water status of plants and the stomatal responses to water availability; b) the hydraulic traits derived from Ѱ isotherms (pressure vs volume curves); c) the impact of the water stress on the hydraulic traits derived from the pressure vs volume curves and on photosynthetic responses; d) the stomatal sensitivity to ABA (only on one of the study sites) and e) their stem hydraulic vulnerability in relation to xylem characteristics.

Results – Acording to the Ѱleaf/Ѱpd relationship (), and contrary to various previous reports, we found Syrah to be an isohydric grapevine variety, while Carménère, an emblematic variety cultivated in Chile, behaved as anisohydric. Syrah resulted to be more variable in terms of , gs50 and gs12 (the pd upon which stomata is reduced down to a 50% and 12%), 0 and tlp (the at full turgor and the  at turgor loss point), likely associated to the higher genetic variability of Syrah compared to that of Carménère. Also, Carménère, the anisohydric variety was capable of osmotic adjustment and was more sensitive to ABA at the stomatal level, two traits typical of anisohydric species, contrary to that observed in Syrah. Even though the capacity to maintain stomata open, theoretically, would imply a lower energy load into the photosynthetic systems, both varieties reduced their photosynthetic capacity up to a similar extent upon drought. Finally, Syrah, despite having wider xylem vessels than Carménère, is less vulnerable to cavitation, and had a lower hydraulic safety margin, typical of isohydric species. We will discuss our results in terms of the genetic variability of the varieties regarding the consistency of their hydraulic responses, the importance of the environment, the degree of isohydry in relation to stomatal responses to critical thresholds as well as drought resistance, and the implications for photosynthesis in the long term.