The Dynamic Simulation of Water Use Efficiency in Potted Apple Trees under Drought Stress

Abstract

This paper simulated the dynamic changes of the Instantaneous Water Use Efficiency (WUEI) of leaves by constructing a coupled model related to net photosynthetic rate (Pn) and transpiration speed (Tr) of apple trees under different moisture conditions. Model parameters were determined through the potted apple tree experiment under gradual drought conditions (Malus domestica Borkh. cv. Fuji). Numerical simulation results showed that WUEI increased as the potential of soil water decreased. When the potential of soil water dropped to less than -1.2 MPa, WUEI turned out to be negatively correlated with it. In the meanwhile, WUEI rapidly increased with increasing CO2 concentration and humidity, but with decreasing temperature. Simulation also revealed that WUEI increased with the Photosynthetically Available Radiation (PAR) when PAR was below the light saturation point, but experienced the minimal changes when PAR exceeded the light saturation point. Over the 24 hours of a day, the WUEI of the apple tree canopy appeared as a bimodal curve. In the daytime the WUEI value was relatively stable, which reached about 2-3mmol·mol-1 with abundant water supply provided. All the above results proved that the coupled model can simulate the dynamic changes of WUEI in potted apple tree under drought stress.