Environmental influences on evapotranspiration in wheat-maize rotation systems under diverse hydrological regimes in the Guanzhong Plain, China

Evapotranspiration (ET) is a crucial hydrological process in terrestrial and agricultural ecosystems, and is a key factor driving climate change dynamics. Understanding the variability of ET and how it responds to controlling factors helps describe the impact of environmental changes on agricultural ecosystems. This study analyzes long-term continuous measurements from an Eddy Covariance (EC) system in wheat-maize rotation fields in the Guanzhong Plain in China. Using structural equation modeling (SEM), we investigated the regulatory roles of environmental and biological factors on ET, and the mechanisms controlling ET for summer maize and winter wheat under varying hydrological and climatic conditions. The results indicate that the eight-year average ETa during the summer maize season ranged from 259 to 348 mm; during the winter wheat season, it ranged from 369 to 513 mm. The adjusted SEM explained 64 % of the variation in daily ETa during the summer maize season and 80 % during the winter wheat season. Photosynthetically active radiation (PAR) was the primary controlling factor for both seasons, with air temperature (Tair) also playing a significant role. Leaf area index (LAI) was an important mediator for ET, and had a greater effect during the winter wheat season than during the summer maize season. Vapor pressure deficit (VPD) and soil water content (SWC) had a more significant impact on ET during the summer maize season than during the winter wheat season. The ET response to environmental factors varied significantly under different hydrological and climatic conditions. Specifically, the total effect of PAR on ETa increased with increased moisture availability and decreased temperature; the trend was opposite for Tair. This indicates that high temperatures and drought conditions may increase the sensitivity of ET to temperature changes, and decrease the sensitivity of ET to radiation changes. This study explains the variability of evapotranspiration in agricultural ecosystems and associated controlling factors, providing important insights about how agricultural evapotranspiration responds to vegetation phenology under future climate change scenarios. These investigations help optimize water resource utilization and allocation in agricultural fields.