Fisiologia e metabolismo foliar em duas variedades de videira sujeitas a um ciclo de défice hídrico e reidratação

Abstract

This work aimed to compare two grapevine varieties grown in Portugal, Syrah and Touriga Nacional, in terms of their physiological and biochemical behavior in response to a cycle of severe water stress followed by rehydration. Vines were subjected to either continuous watering (FI) or not watered for 21 days and rehydrated after leaf water potential at predawn reach-1.1 MPa (NI). Observations took place at four stages: i) immediately before water withdrawal (day 0), ii) Maximum stress (day 21), iii) two days after rehydration (day 23) and iv) six days after rehydration (day 27). We measured leaf water potential at pre-dawn (Ψ<inf>pd</inf>) and at midday (Ψ<inf>md</inf>), stomatal conductance to water vapor (gs), net photosynthesis (An), transpiration (E), the sub-stomatal CO<inf>2</inf> concentration (ci) and chlorophyll a fluorescence. The contents of total chlorophyll content and hydrogen peroxide (H<inf>2</inf>O<inf>2</inf>) in leaves were determined as well. All parameters were negatively affected by water stress, except basal fluorescence (Fo). The recovery capacity in terms of water potential and leaf gas exchange was similar in both varieties but it proved incomplete, in particular for net photosynthesis. The variety 'Touriga Nacional' showed higher degradation of chlorophyll and higher levels of H<inf>2</inf>O<inf>2</inf> in leaves than the 'Syrah' variety, which may explain the high susceptibility of Touriga to leaf senescence and leaf drop under water stress conditions in the field.