Future CO2 , warming and water deficit impact white and red Tempranillo grapevine: Photosynthetic acclimation to elevated CO2 and biomass allocation.

Due to the CO2 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 (CO2 , temperature and water availability) simultaneously in grapevine are scarce. The present work aims to analyze the combined effects of high CO2 (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, CO2 , 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. CO2 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 CO2 were reduced by long-term exposition to elevated CO2 . Exposure to such high CO2 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 CO2 .