Effects of size and microclimate on whole-tree water use and hydraulic regulation in Schima superba trees

Background. Plant-water relations have been of significant concern in forestry and ecology studies in recent years, yet studies investigating the annual differences in the characteristics of inter-class water consumption in trees are scarce. Methods. We classified 15 trees from a Schima superba plantation in subtropical South China into four ranks using diameter at breast height (DBH). The inter-class and wholetree water use were compared based on three parameters: sap flux density, whole-tree transpiration and canopy transpiration over two years. Inter-class hydraulic parameters, such as leaf water potential, stomatal conductance, hydraulic conductance, and canopy conductance were also compared. Results. (1) Mean water consumption of the plantation was 287.6 mm over a year, 165.9 mm in the wet season, and 121.7 mm in the dry season. Annual mean daily water use was 0.79 mm d(-1) with a maximum of 1.39 mm d(-1) (2) Isohydrodynamic behavior were found in S. superba. (3) Transpiration was regulated via both hydraulic conductance and stoma; however, there was an annual difference in which predominantly regulated transpiration. Discussion. This study quantified annual and seasonal water use of a S. superba plantation and revealed the coordinated effect of stoma and hydraulic conductance on transpiration. These results provide information for large-scale afforestation and future water management.