Abstract: To research the nighttime water recharge in Acacia mangium trunk is helpful to improve the preciseness of canopy transpiration- and stomatal conductance estimation, and to further understand the time lag between canopy transpiration and stem sap flow. In this study, the whole-tree sap flow in A. mangium forest was measured by Granier’s thermal dissipation probe for over two years in Heshan Mountain of Guangdong Province, and the environmental factors, including relative humidity (RH), rainfall, vapor pressure deficit (VPD), photosynthetically active radiation (PAR), and air temperature (T) were recorded simultaneously. The nighttime water recharge of A. mangium trunk was analyzed on daily scale and monthly scale, and the results indicated that the sap flow density was smaller at nighttime than at daytime, and the range of nighttime sap flow density was wider in dry season than in wet season. The major duration of water recharging was from sunset to midnight. No significant differences were observed among inter-annual nighttime water recharges. Nighttime water recharge had no significant correlation with environmental factors, but correlated well with the diameter in the breast, height, and crown width of A. mangium. In dry season, the contribution of nighttime water recharge to total transpiration had significant correlations with daytime transpiration, total transpiration, VPD, PAR and T; while in wet season, it was significantly correlated with daytime transpiration and total transpiration.

Key words: Soil solution chemistry, Dissolved aluminum, Dissolved organic carbon Forest stand, Eco-chem-istry