Dynamics and environmental controls of energy exchange and evapotranspiration in a hilly tea plantation, China

Abstract

Tea plantations (Camellia sinensis) are expanding rapidly in China during the last two decades. However, the detailed knowledges of water vapor and energy fluxes in tea plantation ecosystem are still absent. In this study, we explored the temporal variation in water vapor and energy fluxes over a tea plantation through the analysis of 4-year (2014–2017) fluxes data obtained via the eddy covariance technique. The results showed that latent heat flux (LE) was the main consumer of net radiation (Rn). LE/Rn ranged from 0.50 to 0.67 at the pruning period (April-June) and dormant period (December-March). At the mid-growing season (July-September) and late growing season (October-November), LE accounted for more than 0.75 of Rn, except for the mid-growing season in 2016. Sensible heat flux (H) showed an almost opposite trend to LE, while seasonal variation of soil heat flux (G) was small. The interannual actual evapotranspiration (ETa) was stable in tea plantation ranging from 694–741 mm (CV = 2.9 %) despite a large interannual variation in precipitation (CV = 23.9 %). The average annual ETa accounted for 49 % of the corresponding annual precipitation. The highest measured daily ETa reached 5.2–6.9 mm in July for both years. The seasonal variations of daily ETa were strongly related to the Rn. At the mid-growing and late growing seasons, Rn was the limiting factor on ETa with high Priestley-Taylor coefficient (α, 1.05) and decoupling coefficient (Ω, 0.69). In addition, low temperature physiological dormancy and vapor pressure deficit (VPD) at the dormant period and pruning of canopy at the pruning period leading low leaf area index (LAI) also played secondary impacts on ETa through their eff ;ects on canopy surface conductance (< 10 mm s−1). Moreover, ETa would be significantly affected by soil water availability at the mid-growing season due to the large water demand for growth, when the soil water was below 0.12 m3 m−3.