Analysis of pathway differences in sap flow response of Prunus salicina under water gradient conditions

• A structural equation model (SEM) was applied to analyze sap flow responses of Prunus salicina under four soil moisture regimes. • Sap flow was jointly driven by air temperature, soil moisture, and wind speed, with the dominant factors varying across treatments. • The explanatory power of environmental factors was highest under drought and natural conditions, and lowest under full irrigation. • Different water treatments significantly altered the pathways and strength of environmental influences on sap flow. • Results provide theoretical support for precision irrigation and water-saving strategies in cold-region plum orchards. This study examined the responses and regulatory pathways of sap flow in Prunus salicina under different soil water gradients. Four irrigation treatments were applied: sufficient irrigation (G1), moderate irrigation (G3), severe water stress (G2), and natural control (G4). Sap flow, meteorological, and soil moisture data were analyzed using structural equation modeling (SEM) to quantify the direct and indirect effects of environmental factors. Results indicated that the dominant drivers and structural pathways of sap flow varied m markedly with soil moisture. Under natural control, sap flow was mainly governed by atmospheric drought, with vapor pressure deficit (VPD, 0.800) and relative humidity (0.640) as the principal positive factors. Under severe water stress, air temperature (0.439) became the main driver, while under moderate irrigation, wind speed (-0.445) and soil moisture (0.265) jointly influenced sap flow. In the sufficient irrigation regime, soil moisture dominated (0.265) as meteorological influences weakened. All models showed good fit (CFI, GFI > 0.95). The findings highlight a transition in sap flow regulation from meteorological to soil control, demonstrating the utility of SEM in capturing dynamic hydraulic responses and providing a theoretical basis for precision irrigation in cold-region orchards.