Energy partitioning and evapotranspiration in a black locust plantation on the Yellow River Delta, China

Plantations of woody tree species play a crucial role in ecological security along coastal zones. Understanding energy partitioning and evapotranspiration can reveal land-atmosphere interaction processes. We investigated energy fluxes, evapotranspiration, and their related biophysical factors using eddy covariance techniques in a black locust (Robinia pseudoacacia L.) plantation in 2016, 2018, and 2019 on the Yellow River Delta. Downward longwave radiation offsets 84-85% of upward longwave radiation; upward shortwave radiation accounted for 12-13% of downward shortwave radiation. The ratio of net radiation to downward radiation was 18-19% over the three years. During the growing season, latent heat flux was the largest component of net radiation; during the dormant season, the sensible heat flux was the dominant component of net radiation. The seasonal variation in daily evapotranspiration was mainly controlled by net radiation, air temperature, vapor pressure deficit, and leaf area index. Black locust phenology influenced daily evapotranspiration variations, and evapotranspiration was greater under sea winds than under land winds because soil water content at 10-cm depth was greater under sea winds during the day. Seasonal patterns of daily evaporative fraction, Bowen ratio, crop coefficient, Priestley-Taylor coefficient, surface conductance, and decoupling coefficient were mainly controlled by leaf area index. The threshold value of daily surface conductance was approximately 8 mm s(-1) over the plantation.