Transpiration and water use strategies of three economic tree species in a semi-arid afforestation region

Determining transpiration characteristics and water use strategies of economic tree species is crucial for adaptability evaluations and orchard management in semi-arid areas. This research focused on peach (Prunus persica), walnut (Juglans regia L.), and apple (Malus pumila) trees to quantify variations in sap flow using the thermal dissipation probe method over two consecutive years on the Loess Plateau of China. We calculated transpiration (Tr) and canopy conductance (g_c) for the three tree species, and monitored meteorological factors, soil water content (SWC), and leaf area index (LAI). On sunny days, the diurnal results revealed single-peak curves of sap flux densities for all three tree species, with peach and apple trees exhibiting earlier peak times than walnut trees. Tr and g_c values varied in accordance with the intrinsic phenology of each tree species. The environmental and physiological factors affecting Tr differed among the three species, and Rs was the primary meteorological influencing factor affecting the Tr of peach and apple trees, while walnut trees Tr was mainly controlled by VPD. No significant correlations occurred between daily Tr and relative extractable water (REW) for any of the tree species. However, on a monthly scale, LAI positively correlated with Tr for peach and walnut trees but not for apple trees. Furthermore, the water use strategies differed among the three tree species, with peach and apple trees exhibiting higher stomatal sensitivity than walnut trees. These findings highlight the impact of tree phenology on seasonal variations in Tr and g_c, leading to different influencing factors for transpiration among the three species.