Patterns, magnitude and controlling factors of hydraulic redistribution by Populus euphratica roots.

As an important ecological process, it is fundamental for understanding the eco-hydrological consequences of hydraulic redistribution to illuminate its patterns, magnitude and controlling factors. We selected Populus euphratica, which of constructive species located at the lower reaches of Heihe River in northwestern China, to identify patterns and quantize the magnitude and controlling factors of hydraulic redistribution by the heat ratio method. We not only confirmed the previous knowledge on hydraulic lift, in which rates of flow in lateral roots of P. euphratica were negative during the night, but also demonstrated that water can transport from moist topsoil to dry subsoil after rain, i. e. hydraulic descent. In addition, water also moved from lateral moist soil layer to opposite dry soil layer after lateral irrigation, i. e. lateral redistribution. The magnitude of hydraulic redistribution of P. euphratica roots based on negative sap flow in lateral roots ranged from 0.16 to 0.26 kg/ day with an average of 0.21 kg/ day, which can accounts for 38.75% of transpiration of the next day. The correlation and stepwise regression analysis demonstrated that hydraulic redistribution was significantly positive correlated with vapor pressure deficit, air temperature and soil moisture content, instead negative correlation with relative humidity, in which vapor pressure deficit and soil moisture content were main controlling factors of hydraulic redistribution.