Abstract: Evapotranspiration (ET), vapor pressure deficit (VPD) and water use efficiency (WUE) are crucial components of the hydrological cycle in forest ecosystems, serving as indicators that reflect the intricate coupling of carbon and water fluxes within the ecosystem. The cold temperate zone, being ecologically fragile and sensitive to climate change, accentuates the significance of exploring the variation characteristics of the dynamics of hydrological processes of a Larix gmelinii forest ET, VPD and WUE were measured in the June to August growing season and the April, May, September and October freeze–thaw period from 2011 to 2016. A structural equation model (SEM) quantitatively analyzed the impact of environmental factors on ecohydrological variables. The results reveal that: (1) Daily average ET in the growing season was significantly higher than in the freeze–thaw period. WUE showed the opposite. Peaks for both ET and VPD occurred in July. In contrast, the freeze–thaw period saw maximum ET and VPD, and minimum WUE in May. July and May emerged as the most active months for hydrological processes in the ecosystem; (2) During the growing season, VPD was influenced by relative humidity (RH) and temperature (T_a), ET responded negatively to solar radiation, and WUE negatively to VPD. Throughout the freeze–thaw period, the ecosystem experienced heat stress, and ecohydrological processes were influenced by T_a. This study provides valuable references for further research on hydrological cycles in forest systems within cold temperate zones.

Key words: Evapotranspiration, Vapor pressure deficit, Water use efficiency, Larix gmelinii, Daxing’an Mountains