Effect of pruning on the stem sap flow of typical sand-fixing plant Haloxylon ammodendron

Haloxylon ammodendron is a typical tree species known for windbreak and sand fixation. In recent years, some H. ammodendron forests have shown signs of decline, which has seriously affected the windbreak and sand fixation benefits of the shelter forest system. Pruning is an effective tending management measure to reduce water stress of the tree in arid areas. Understanding the changes in the sap flow rate of the tree under different pruning treatments and its relationship with meteorological factors can help to reveal the water transport law of H. ammodendron. In this study, we monitored the sap flow of the species and meteorological factors under different pruning treatments in Ulan Buh Desert using a thermal diffusion sap flow meter and automatic weather station. The results showed that the hourly scale change of sap flow under different pruning treatments (pruning 75%, pruning 50%, pruning 25%, pruning 0) is a “broad peak” pattern, whereas, that without pruning is a “single-peak” pattern. The descending order of average daily water consumption of the species under different pruning treatments is pruning 50% (15.37 kg) > pruning 75% (11.77 kg) > no pruning (9.37 kg) > pruning 0 (3.29 kg) > pruning 25% (2.03 kg). The sap flow rate has an asymmetric response to solar radiation, air temperature, relative humidity and saturated water vapor pressure difference. The sap flow under no pruning, pruning 75%, pruning 50%, pruning 25% and pruning 0 treatments showed a counterclockwise ring or counterclockwise oblique 8-shaped pattern with solar radiation and relative humidity, respectively, and exhibited a clockwise ring or clockwise oblique 8-shaped with air temperature. The vapor pressure deficit Principal component analysis showed that solar radiation is the primary meteorological factor affecting the hourly and daily sap flow rate of the species under pruning and no pruning treatment. Based on the water consumption, it is suggested that pruning 25% treatment is the best for the tree in Ulan Buh Desert, which can provide a theoretical basis for the estimation of ecological water demand and tending management of H. ammodendron forest in the future.