Leaf water use efficiency in a 'tendone' trained canopy: a contribute to the ecophysiological characterization of a grapevine growing system

A research project aiming at the ecophysiological characterization of typical viticultural systems has included investigation on table grape vineyard trained to overhead 'tendone' system. It has a large horizontal canopy where primary shoots are tied to a wire grid parallel to the soil, while the lateral shoots grow upward and the clusters hang below the trellis. The actual distribution of the photosynthetic water use efficiency within this type of canopy architecture was studied, in the Apulia region, South Italy, at a vineyard of moderate vigor managed without any type of plastic protection to force the grape production. In this tendone foliage, differently from what generally reported for vertical trained canopies, the mutual leaf shading was found not high because of the lateral shoot position, the leaf blade angle, and the moderate vigor, thus the leaf layer below the top leaf surface received 86% of the maximum PPF available at the external leaf layer, while the lower layers received 68 and 47% of it. Compared to the external leaf surface, the internal leaves lowered their photosynthetic rates by 27-67% and the transpiration rate by 18-41%. As a consequence, the photosynthetic water use efficiency of the internal leaf layers decreased by 11-44%, thus it appeared to be depressed not as much as expected basing on what was found with other types of canopy architecture.