Environmental controls on transpiration of Schima superba trees with different tree sizes under ten years’ climate fluctuations in south subtropics, China

Abstract

Transpiration is an important component of the hydrological cycle for forest ecosystems. Long-term studies on how climate fluctuations influence canopy transpiration, as well as regulation mechanisms, are still lacking in southern subtropics. Based on a ten-year sap flow monitoring, we analyzed the long-term patterns of tree water use and environmental regulation of transpiration for a Schima superba forest under climate fluctuations. Results showed that the sap flux density (JS) and whole-tree transpiration (Et) in wet seasons were higher than those in dry seasons. Stand transpiration (Eg) upscaled from JS varied significantly among the experimental years and 11.9–33.6% of annual precipitation were transpired by the canopy. Extreme meteorological events increased transpiration anomalies during the decade. Large trees took up the most proportion of stand transpiration and exhibited greater sensitivities to environmental factors than medium and small trees. Evaporative demands had a higher effect on whole tree water use (Qd) than water supply due to adequate precipitation in this area. The variation partitioning analysis indicated that Qd was mainly influenced by energy factor (net radiation and sunshine duration), while the effect of precipitation on Qd was the lowest among all environmental factors. Furthermore, the shared effects of vapor pressure deficit (VPD) and energy factor accounted for the biggest portion of the variance of Qd. These results revealed the influence of environmental factors on forest transpiration in subtropics, and provided valuable implications for predicting the hydrological dynamics under future global climate scenarios, thus improving water resources management in catchments.