Diurnal and seasonal changes in whole-tree transpiration of Acacia mangium.

In order to explore the water use characteristics of re_vegetation tree species in degraded hilly lands in south China,sap flow of Acacia mangium was measured continuously using Granier's thermal dissipation probe method.Simultaneously,environmental factors such as photosynthetically active radiation(PAR),global radiation,air temperature,air relative humidity,and soil relative humidity were also monitored.Sap flux density at four orientations(east,south,west and north) on the trunk was significantly different,and the sap flux density at different orientations was highly pair_wise correlated;but the regression coefficients were different among individual trees and varied seasonally.The seasonal patterns of sap flow of the trees were all similar.The correlations between sap flow,PAR,global radiation,air temperature and VPD were significant at any time scales(hourly,daily and monthly).However, there was no significant correlation between sap flow and relative soil water content at above time scales.The mean annual sap flow per tree was(9 380.9) kg,while individual tree sap flow ranged from 6 229.8 to 14 076.6 kg according to individual tree's social status and canopy size.