Evolution of midday leaf and stem water potential and their correlations with other ecophysiological measurements in three Galician grapevine cultivars

Abstract

The measurement of leaf water potential has been used to monitor the water relations of grapevines since the development of the pressure chamber. However, midday leaf water potential depends greatly on the weather conditions of the measurement day; thus, it may not provide a reliable estimate of plant water status. Stem water potential is less variable than leaf water potential and it is commonly used for irrigation scheduling. Nevertheless, other ecophysiological measurements may indicate grapevine water status. In this sense, a study was conducted to compare two measurements of determining water status of grapevines in the field and to correlate them with other ecophysiological variables such as soil water content, leaf stomatal conductance and chlorophyll fluorescence. Measurements were taken on “Torrontés”, “Godello” and “Mencía” cultivars over the 2012 growing season. The vineyards were located in the Designation of Origin Ribeiro (Galicia, Spain). Leaf (ψ_l) and stem (ψ_s) water potentials were measured at midday using a pressure chamber. In addition, stomatal conductance to water vapour (g_s) and chlorophyll fluorescence were measured at midday on the same leaves used for determining ψ_l. Values obtained for ψ_l and ψ_s in this study ranged from –0.42 to –1.27 and –0.15 to –0.53 MPa, respectively. Linear regression analysis of ψ_l as a function of ψ_s resulted in r values of 0.81, 0.64 and 0.56 for Godello, Torrontés and Mencía, respectively. The linear correlations among stem water potential and other ecophysiological measurements were different depending on the cultivar. Hence, stomatal conductance was correlated to stem water potential for Godello and Mencía but not for Torrontés. Electron transport rate was correlated to stem water potential for the three studied cultivars. Other chlorophyll fluorescence parameters did not present correlation to water potential for the three cultivars considered in this study. However, the relation between the photosystem II activity and the photosynthetic active radiation was highly correlated to stem water potential in the three cultivars accounted for in this study. In conclusion, water stress did not affect considerably to the grapevine photosynthetic activity under the studied conditions. Finally, certain ecophysiological parameters such as stomatal conductance and electron transport rate may be considered as good indicators of grapevine water status.