Measurements of water dissipation and water use efficiency at the canopy level in a peach orchard

Water deficit is the main limiting factor for agricultural production in the dry regions of northern China. Previous studies on water–plant relationships in fruit trees have focused mainly on ecological, physiological and molecular responses to water stress at the leaf or tree-scale; few equivalent studies have been conducted at the ecosystem-scale. In this study, we monitored water vapour exchange and water use efficiency (WUE) in a no-till, 12-year-old peach orchard using an eddy covariance technique. Daily average values of actual evapotranspiration (ETa) and WUE were 2.3 ± 2.1 mm and 0.44 g CO2 kg−1 H2O, respectively, across the monitoring period. Daily changes in WUE at the canopy level were strongly influenced by atmospheric vapour pressure deficit (VPD) during stages rapid plant growth. The rank order of WUE across developmental stages was: fruit post-harvest stage > fruit de-greening and red-colouring stage > flowering period and early fruit enlargement stage. The trends of water dissipation and WUE both had single peaks. During the late period of fruit enlargement, the rate of actual evapotranspiration was very high, reaching a daily maximum value of 7.1 mm d−1. Average daily WUE ranged up to 2.1 g CO2 kg−1 H2O, peaking after fruit harvest. The annual cumulative actual evapotranspiration reached 790.6 mm, with a crop coefficient 1.08. In conclusion, WUE was strongly influenced by VPD in the daytime during peach development, and the key stage of water requirement occurred in the period following the onset of fruit ripening in the orchard.