Nocturnal Water Use Partitioning and Its Environmental and Stomatal Control Mechanism in Caragana korshinskii Kom in a Semi-Arid Region of Northern China.

As an important aspect of plant water consumption, nocturnal water use (E_n) behavior provides reliable information on the effect of plantation carbon and water budgets at stand and regional scales. Therefore, quantifying E_n and its environmental and stomatal controlling mechanisms is urgent to establish adaptation strategies for plantation management in semiarid regions. With the help of the sap flow technique, our study investigated the seasonal variations in canopy transpiration and canopy conductance in a Caragana korshinskii Kom plantation. Environmental variables were measured concurrently during the growing seasons of 2020 and 2021. The results indicated that the average E_n values were 0.10 mm d⁻¹ and 0.09 mm d⁻¹, which accounted for 14% and 13% of daily water use, respectively, over two years. The proportions of nocturnal transpiration (T_n) to E_n were approximately 49.76% and 54.44%, while stem refilling (R_e) accounted for 50.24% and 45.56% of E_n in 2020 and 2021, respectively, indicating that C. korshinskii was able to draw on stored stem water to support transpiration. E_n was predominantly affected by nocturnal canopy conductance (G_c–n), air temperature (T_a–n) and wind speed (u_2-n). In contrast, G_c–n and T_a–n explained the highest variation in T_n and nocturnal vapor pressure (VPD_n), and u_2-n explained the highest variation in R_e. Total effects of the five environmental and stomatal variables explained 50%, 36% and 32% of E_n, T_n and R_e variation, respectively. These findings could enable a better understanding of nocturnal water use dynamics and their allocation patterns in C. korshinskii plantations on the Bashang Plateau. Moreover, our results reveal the water use strategies of artificial shrubs and highlight the importance of incorporating nocturnal water use processes into large-scale ecohydrological models in semiarid regions. [ABSTRACT FROM AUTHOR]