Actual transpiration and canopy resistance in a Mediterranean vineyard irrigated with saline water

Irrigation with saline water is practiced in countries prone to water scarcity, in arid and semi-arid climates. In a Mediterranean climate (Sicily, southern Italy), transpiration and canopy resistance were determined in a vineyard (Syrah grafted on Paulsen 1103) irrigated with water at two salinity levels. One section of the experimental plot was irrigated with water of low salinity (electrical conductivity ECw = 0.6 dS m-1); the other section received irrigation water at higher salinity level (ECw = 1.6 dS m-1). Actual vines transpiration was measured by a thermal dissipation sap flow method, in two growing seasons (2008 and 2009). Canopy transpiration (Tr) and resistance (rc), the latter calculated using the Penman-Monteith equation, were analyzed on hourly and daily time scale. Moreover, the trends in canopy resistance were evaluated in relation to main micrometeorological variables (global radiation and vapor pressure deficit). In the ECw 1.6 treatment, canopy transpiration was lower and its values, cumulated through the experimental period, were 20% and 16% lower than in the ECw 0.6 treatment, in 2008 and 2009, respectively. A rudimentary estimate of the relationship between cumulated canopy transpiration and soil salinity was also made, and a threshold value of relative transpiration was identified at soil electrical conductivity (ECe) = 1.4 dS m-1. Hourly values of rc in ECw 1.6 were higher than in ECw 0.6 and the response patterns of rc to global radiation and to vapor pressure deficit were different at different salinity levels.