干旱区生态环境知识资源中心

Grapevine water use efficiency (WUE) is becoming a key issue in semi-arid areas as the production and quality of a harvest largely depends on the use of important water volumes in areas that are typically characterised by water scarcity during the grapevine growing season. Therefore, improving water use efficiency is a challenge to secure the environmental sustainability of viticulture in these areas. WUE is commonly measured at the leaf level because portable equipment of leaf gas exchange rates facilitates the simultaneous measurement of photosynthesis and transpiration. However, when those measurements are compared to the daily integrals or whole plant estimations, the relationship sometimes results in high and sometimes in low correspondence. Scaling up from single leaf to whole plant WUE was attempted by comparing daily integrals of AN/E with midday values, showing a poor relationship that impoverished as water stress intensified. The main objective of the present work was to evaluate the importance of the spatial and time variations of carbon and water balances at the leaf and plant level. The leaf position inside the canopy showed a marked effect on the instantaneous and daily integrals of leaf WUE. The night transpiration and respiration rates were also evaluated, as were the shoot and root respiration contributions to the total carbon balances. Two main components were identified to solve the gap between leaf and whole plant WUE, the important effect of leaf position on the daily carbon gain and transpiration and the large flux of carbon losses by dark respiration. Moreover, these results also showed the importance of some as yet unexplored targets to improve the WUE in grapevines.