Soil Water Use and Adaptive Regulation of Schima superba in the Dry and Wet Seasons

Abstract:

In order to understand the difference in soil water use of Schima superba in dry and wet seasons, the sap flux densities (Js) of S. superba were continually monitored using Granier's thermal dissipation probes (TDP). Based on the measurements of leaf water potential (Ψ_L), parameters of hydraulic structures, such as leaf area index (LAI), and Huber value (A_S:A_L), in combination of the synchronized monitoring environment factors, the dry/wet seasonal changes in whole-tree hydraulic conductance (K_L), canopy stomatal conductance (G_S) and effective water storage for transpiration (Q) of S. superba were analyzed. The results showed that the soil water deficit in the dry season increased the resistance of water absorption and transpiration of S. superba. However, the G_S of S. superba was sensitive to the vapor pressure deficit (VPD) to keep midday leaf water potential (Ψ_L-mid), water potential gradient between leaves and the soil (ΔΨ_S-L) in dry and wet seasons. Moreover, the LAI、K_L and G_S of S. superba decreased to effectively regulate transpiration in the dry season. Meanwhile, the high contribution of effective water storage for transpiration (Q) to daily transpiration and Q per unit leaf area in the dry season would partially compensate the water stress. Since the S. superba plantation could maintain a vigorous transpiration with those adaptive regulations in the dry season during which it still had sufficient solar and thermal resources in south China, the whole-tree water use per unit leaf area of S. superba in the dry seasons was kept similar to that in wet seasons. Therefore, it was suggested that the regulating of K_L and G_S, the hydraulic compensation effect of Q, and the hydraulic characteristics, could to some extent explain that the whole-tree water use per unit leaf area of S. superba remained constant in the dry and wet seasons, and SWC had no significant effect on transpiration.