Shoot hydraulic characteristics, plant water status and stomatal response in olive trees under different soil water conditions

To evaluate the impact of the amount and distribution of soil water on xylem anatomy and xylem hydraulics of current-year shoots, plant water status and stomatal conductance of mature 'Manzanilla' olive trees. Measurements of water potential, stomatal conductance, hydraulic conductivity, vulnerability to embolism, vessel diameter distribution and vessel density were made in trees under full irrigation with non-limiting soil water conditions, localized irrigation, and rain-fed conditions. All trees showed lower stomatal conductance values in the afternoon than in the morning. The irrigated trees showed water potential values around -1.4 and -1.6 MPa whereas the rain-fed trees reached lower values. All trees showed similar specific hydraulic conductivity (K (s)) and loss of conductivity values during the morning. In the afternoon, K (s) of rain-fed trees tended to be lower than of irrigated trees. No differences in vulnerability to embolism, vessel-diameter distribution and vessel density were observed between treatments. A tight control of stomatal conductance was observed in olive which allowed irrigated trees to avoid critical water potential values and keep them in a safe range to avoid embolism. The applied water treatments did not influence the xylem anatomy and vulnerability to embolism of current-year shoots of mature olive trees.