Tree-to-tree variation in plant-based measurements as indicators of orange water status

A study was conducted in order to determine the sensitivity of measured indicators of the plant water status in a citrus orchard. In ten adult orange (Citrus sinensis) trees, grafted on sour orange (C. aurantium) rootstocks and drip irrigated every second day, sap flow by Granier TDP probes, leaf and xylem water potential, gas exchange and leaf and canopy thermal imaging were hourly monitored all over the day. The evaluations were performed during two separate clear-sky days with different environmental conditions, respectively in the summer and autumn seasons. Variations of environmental components (reference evapotranspiration, solar radiation, vapour pressure deficit and temperature) were recorded. Each measurement tecnique resulted effective to perceive continuous plant water status at the proper scale (treeand orchard level). In particular, transpiration rate, water deficit stress indicators, stomatal conductance and closure were related to diurnal changes in ET0 and net radiation. Tree-to-tree variations in the diurnal dynamics of tree gas exchange were evaluated to develop up-scaling rules of tree-level water consumption measurements.