Abstract:
Photosynthesis in C3 plants is CO2 limited and therefore any increase in Rubisco carboxylation substrate may increase net CO2 fixation, unless plants experience acclimation or other limitations. These aspects are largely unexplored in grapevine. Photosynthesis analysis was used to assess the stomatal, mesophyll, photochemical and biochemical contributions to the decreasing photosynthesis observed in Tempranillo grapevines (Vitis vinifera) from veraison to ripeness, modulated by CO2, temperature and water availability. Photosynthesis and photosystem II photochemistry decreased from veraison to ripeness. The elevated CO2 and temperature increased photosynthesis, but transiently, in both well irrigated (WI) and water-stressed plants. Photosynthetic rates were maxima 1 week after the start of elevated CO2 and temperature treatments, but differences with treatments of ambient conditions disappeared with time. There were not marked changes in leaf water status, leaf chlorophyll or leaf protein that could limit photosynthesis at ripeness. Leaf total soluble sugars remained at ripeness as high as 2 weeks after the start of treatments. On the other hand, and as expected, CO2 diffusional limitations impaired photosynthesis in grapevine plants grown under water scarcity, stomatal and mesophyll conductances to CO2 decreased and in turn low chloroplastic CO2 concentrations limited photosynthetic CO2 fixation. In summary, photochemistry and photosynthesis from veraison to ripeness in Tempranillo grapevine were dominated by a developmental-related decreasing trend that was only transiently influenced by elevated CO2 concentrations.