Future CO 2 , warming and water deficit impact white and red Tempranillo grapevine: Photosynthetic acclimation to elevated CO 2 and biomass allocation

Due to the CO 2 greenhouse effect, elevated atmospheric concentration leads to higher temperatures, accompanied by episodes of less water availability in semiarid and arid areas or drought periods. Studies investigating these three factors (CO 2 , temperature and water availability) simultaneously in grapevine are scarce. The present work aims to analyze the combined effects of high CO 2 (700 ppm), high temperature (ambient +4°C) and drought on the photosynthetic activity, biomass allocation, leaf non‐structural carbon composition, and carbon/nitrogen (C/N) ratio in grapevine. Two grapevine cultivars, red berry Tempranillo and white berry Tempranillo, were used, the latter being a natural, spontaneous mutant of the red cultivar. The experiment was performed on fruit‐bearing cuttings during a 3‐month period, from June (fruit set) to August (maturity). The plants were grown in research‐oriented facilities, temperature‐gradient greenhouses, where temperature, CO 2 , and water supply can be modified in a combined way. Drought had the strongest effect on biomass accumulation compared to the other environmental variables, and root biomass allocation was increased under water deficit. CO 2 and temperature effects were smaller and depended on cultivar, and on interactions with the other factors. Acclimation effects were observed on both cultivars as photosynthetic rates under high atmospheric CO 2 were reduced by long‐term exposition to elevated CO 2 . Exposure to such high CO 2 resulted in increased starch concentration and reduced C/N ratio in leaves. A correlation between the intensity of the reduction in photosynthetic rates and the accumulation of starch in the leaves was found after prolonged exposure to elevated CO 2 .