Characteristics and modelling of sap flow of degraded Populus simonii in areas where the ecology is vulnerable

Abstract

AbstractPlant transpiration plays a crucial role in the water balance of forest stands and water yield in arid and semiarid ecosystems. However, our understanding of the characteristics and modeling of transpiration or sap flow of degraded plantations in vulnerable ecology areas is still limited. In this study, the sap flow velocity (SF) of Populus simonii under different categories of degradation (LD, lightly degraded; MD, moderately degraded; SD, seriously degraded) during the growing season in the water‐wind erosion crisscross region of the Chinese Loess Plateau was continuously monitored and estimated using the modified Jarvis‐Stewart (MJS), modified process‐based (MBTA) and multiple linear regression (MLR) models. We found that the daily SF of P. simonii under the three categories of degradation was significantly different (p < 0.05), and degradation degree was negatively correlated with SF. Soil water deficit significantly reduced SF (p < 0.05). Soil water conditions and P. simonii degradation change the peak time of SF rather than the startup time. Three models give good performance for simulating the daily SF of degraded P. simonii, especially the MJS model. The stress of vapour pressure deficit (VPD) on SF first decreases and then increases with increasing VPD, and the VPD threshold is LD < MD < SD. The results provide a valuable reference for revealing the causes of degradation and assessing the drought resistance of plantation ecosystems in water‐limited areas.