Variability in intrinsic water use efficiency (WUEi) of eight red varieties grown in the center of the Iberian Peninsula during an atypical vintage year

The study was performed in the summer of 2007, the point of confluence of a rather atypical vintage year in the area with abnormally low temperatures after a very humid spring. The experiment was carried out in a fully productive vineyard with espalier cultivation and different varieties in one of the largest terroirs of La Mancha (region in the center of Spain). Eight red varieties, i.e., five traditional varieties of the region (Tempranillo, Garnacha Tinta, Bobal, Tinto Velasco and Moravia Agria) and three international varieties (Merlot, Syrah and Cabernet Sauvignon), were studied.
Daily monitoring of the gas exchange was performed with a portable infrared gas exchange system at different development stages (closure of the bunches, veraison and maturity). The recorded measurements allowed to determine, for each studied variety, the values of net photosynthesis (A_N), stomatal conductance (g_s) and transpiration (E) as well as to calculate intrinsic water use efficiency (WUE_i).
The results showed significant differences between varieties as far as the gas exchange parameters are concerned. Bobal, Moravia Agria and Cabernet Sauvignon showed rather high assimilation rates (A_N) during the day, usually above the rest. In turn, the WUEi proved that the Garnacha Tinta and Tempranillo varieties belong to the most efficient group under moderate water stress conditions.