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The present study aimed: i) to evaluate the impact of the changes in temperature and relative humidity (RH), projected by the year 2100, on grape ripening, and ii) to assess if bunch transpiration is a key physiological process involved in the advancement in grape development under future climate conditions. Fruit-bearing cuttings of Vitis vinifera L. cv. 'Tempranillo' were grown, from fruit set to maturity, in glasshouses under two conditions: 24°C/14°C and 55%/70% RH (day/night) (T) vs 28°C/18°C and 43%/58% RH (T+4). To elucidate the role of bunch transpiration in grape development in a future climate scenario, the bunches of half of the plants in the T+4 glasshouse were sprayed with an antitranspirant (AT+4). T+4 increased bunch transpiration, hastened the ripening process, increasing the rate of total soluble solid (TSS) accumulation and malic acid degradation, and reduced the concentration of total anthocyanins. The application of antitranspirant partially alleviated the effects of combined high temperature and low RH on maturation times, through lower TSS accumulation rates. Berries in AT+4 had the lowest concentrations of anthocyanins and color, likely related to a reduction in light transmittance by the antitranspirant film and to higher anthocyanin degradation due to the longer exposure to elevated temperatures. The results show a negative impact of elevated temperature and low RH on grape composition. The increased bunch transpiration under these conditions played an important role in the changes observed in phenology and sugar accumulation.

Atmospheric CO2 levels and global temperatures are expected to rise in the next decades, and viticulture must face these changes. Within this context, exploiting the intra-varietal diversity of grapevine (Vitis vinifera L.) can be a useful tool for the adaptation of this crop to climate change. The aim of the present work was to study the effect of elevated temperature and elevated levels of atmospheric CO2, both individually and combined, on the growth, phenology and carbon partitioning of five clones of the cultivar Tempranillo (RJ43, CL306, T3, VN31 and 1084). The hypothesis that clones within the same variety that differ in their phenological development may respond in a different manner to the above mentioned environmental factors from a physiological point of view was tested. Grapevine fruit-bearing cuttings were grown from fruit set to maturity under two temperature regimes: ambient (T) vs elevated (ambient + 4°C, T + 4), combined with two CO2 levels: ambient (ca. 400 ppm, ACO2) vs elevated (700 ppm, ECO2), in temperature-gradient greenhouses (TGGs). Considering all the clones, elevated temperature hastened grape development and increased vegetative growth, but reduced grape production, the later most likely associated with the heat waves recorded during the experiment. Plants in the elevated CO2 treatments showed a higher photosynthetic activity at veraison and an increased vegetative growth, but they showed signs of photosynthetic acclimation to ECO2 at maturity according to the C:N ratio, especially when combined with high temperature. The combination of ECO2 and T + 4, mimicking climate change environmental conditions, showed additive effects in some of the parameters analyzed. The clones showed differences in their phenological development, which conditioned some responses to elevated CO2 and temperature in terms of vegetative production and C partitioning into different organs. The work adds new knowledge on the use of different grapevine clones, that c