Impact of environmental and physiological factors during drought stress on sap flow in Robinia pseudoacacia plantations in the loess region of western Shanxi Province of northern China

Objective This study aims to investigate the impact of drought stress on the transpiration process of Robinia pseudoacacia plantations in the loess region of western Shanxi Province, northern China. Additionally, it aims to explore the environmental and physiological mechanisms that regulate transpiration in R. pseudoacacia under drought stress conditions. The findings of this study aim to establish a theoretical basis for the management and water regulation of R. pseudoacacia plantations in the loess region of western Shanxi Province.

Method The research focused on R. pseudoacacia plantations in the loess region of western Shanxi Province. Continuous monitoring of sap flow changes in R. pseudoacacia was to conduct alongside a rainfall interception experiment (the 50% precipitation reduction during the entire growing season). Simultaneously, environmental factors and hydraulic physiological changes were monitored to analyze their collective influence on sap flow.

Result (1) Drought treatment significantly reduced the sap flow rate (J_s) of R. pseudoacacia, with an average of 0.92 g/(cm²·h) under drought treatment, markedly lower than the control treatment’s J_s of 1.87 g/(cm²·h). However, the trend of variation exhibited similarity. (2) Drought treatment had an impact on the relative water content of R. pseudoacacia branches and leaves. Over time, the relative water content decreased with extended drought treatment periods. In varying treatment conditions, both water potential and hydraulic capacitance of R. pseudoacacia branches and leaves exhibited a “V” shaped pattern. Under drought treatment, the water potential of branches and leaves (−1.22 MPa, −0.72 MPa) was lower compared with the control treatment (−1.15 MPa, −0.60 MPa). Moreover, under drought treatment, there was a decrease in the hydraulic capacitance of branches (0.52 g/(cm³·MPa)) and leaves (1.05 × 10⁻² g/(cm²·MPa)). (3) Changes in R. pseudoacacia’s sap flow were influenced by meteorological factors, soil moisture, and hydraulic physiological factors. The primary controlling factors under different treatments were solar radiation. Under drought treatment, the influence of branch and leaf hydraulic capacitance weakened, indicating that R. pseudoacacia under control conditions relied more on tissue hydraulic capacitance to meet transpiration compared with drought treatment.

Conclusion Drought treatment significantly reduces the sap flow rate of R. pseudoacacia, but the trend of variation exhibites similarity. Changes in R. pseudoacacia’s sap flow are influenced by meteorological factors, the primary controlling factors are meteorological factors, soil moisture, and hydraulic physiological factors. These findings contribute to a deeper understanding of transpiration alterations in plantations under drought conditions. Additionally, they hold significant importance in evaluating the stability of plantation ecosystems and eco-hydrological processes in the loess region amidst climate change.