Abstract: The objective of this study was to accurately evaluate the evapotranspiration characteristics of Chinese fir (Cunninghamia lanceolata) plantation and to explore the possibility of estimating the evapotranspiration by Penman-Monteith method (PM). Based on the observation data of meteorological gradient and flux from the National Field Scientific Observation and Research Station of Chinese Fir Plantation Ecosystem in Huitong, Hunan Province from 2016 to 2019, we used the eddy covariance method (EC) to analyze the temporal variation of evapotranspiration (ET) in a Chinese fir plantation, and compared the ET obtained with PM. The results showed that the ET showed single wave diurnal and annual variations. During the day, the maximum ET value appeared at 12:30-13:00, and the minimum value appeared at 0:00-2:30. In the year, the maximum value of ET appeared in July-August, and the minimum value appeared in December-February. The ET increased with increasing net radiation (R_n), air temperature (T_a), and vapor pressure deficit (VPD), while decreased with increasing soil water content (SWC). The main meteorological factors affecting the ET were R_n, T_a, and VPD. The ET obtained by PM and EC were consistent in spring and autumn, but significantly different in summer and winter. The difference of ET obtained by PM and EC showed linear and positive correlations with R_n, T_a, and VPD, but a negative correlation with SWC. The results provided theoretical support for exploring the hydrological process of Chinese fir plantation and the feasibility of estimating its ET by PM.

Key words: Chinese fir plantation, evapotranspiration, temporal variation, Penman-Monteith method, meteorological factor.