Dynamics of evapotranspiration and its relationship with drought in a grain-forage compound ecosystem on the Loess Plateau

Evapotranspiration plays a critical role in the water cycles of ecosystems, directly or indirectly impacting soil moisture and processes including plant growth and carbon cycling. It is influenced by extreme climate. Understanding the dynamics and regulatory mechanisms of evapotranspiration in ecosystems under climate change scenarios is thus crucial for regional water resource management and ecological restoration. A typical grain-forage complex ecosystem in the Loess Plateau serves as the research object in this study, and seasonal variation in evapotranspiration within this grain-forage complex ecosystem and its response to summer drought have been analyzed using eddy covariance continuous monitoring. The results show that: 1) evapotranspiration and environmental factors experience noticeable seasonal oscillations, following a unimodal curve throughout the growing season. Approximately 88.0% of total evapotranspiration occurs within the period spanning April to October; 2) the daily maximum evapotranspiration is 6.3 mm, and the annual cumulative evapotranspiration amounts to 471.5 mm. Cumulative rainfall surpasses cumulative evapotranspiration, resulting in a difference of 226.1 mm between evapotranspiration and precipitation; 3) summer drought causes a certain degree of decline in evapotranspiration by inducing stomatal closure, but has little effect on annual evapotranspiration; 4) air temperature, net radiation, soil moisture, and saturation vapor pressure deficit are identified as factors contributing to the seasonal variability in evapotranspiration in this grain-forage combined ecological system, but the most prominent effectors are net radiation and saturated vapor pressure difference. These findings offer a theoretical basis for the management of grain-forage combined ecological systems and efficient water utilization in the Loess Plateau.