Response of sap flow of in Liupan Mountain to drought types.

With forest in the Xiangshui River sub-basin of the Liupan Mountain area as test material, we monitored sap flow in using the thermal diffusion probe during the growing season (from May 13th to September 30th) of 2022 and measured meteorological conditions and soil moisture to explore the water utilization patterns of forest under different drought types. The results showed that the piecewise linear function could accurately reflect the variation of the sap flow rate with soil relative extractable water (REW) and vapor pressure deficit (VPD). Based on the thresholds of the piecewise function, the drought conditions in this area were classified into four types: non-drought (REW≥0.37 m·m, VPD<0.99 kPa), atmospheric drought (REW≥0.37 m·m, VPD>0.99 kPa), soil drought (REW<0.37 m·m, VPD<0.99 kPa), and combined drought (REW<0.37 m·m, VPD>0.99 kPa). The average sap flow rate of was the highest under atmospheric drought (0.042 mL·cm·min) and the lowest under soil drought (0.022 mL·cm·min). The dominant factors influencing the sap flow rate varied across drought types. Under non-drought types, the dominant factors of sap flow were VPD and solar radiation (). Under soil drought, the main influencing factor of sap flow was . Under atmospheric drought and combined drought, the main influencing factors of sap flow were REW and . When facing drought stress, would initiate trunk sap flow earlier for trunk water replenishment, with soil moisture as the main limiting factor.