Variation Characteristics Of Evapotranspiration Of Camellia Oleifera Forest In Subtropical Hilly Region

Evapotranspiration mainly occurs in the soil-plant-atmosphere system（SPAC）,and crop evapotranspiration（or ET）is the most important component of water consumption in agriculture.By analyzing the characteristics of evapotranspiration of Camellia oleifera forest in subtropical hilly region under natural conditions,and distinguishing and quantifying it from soil evapotranspiration and plant evapotranspiration,it can provide a theoretical basis for rational allocation of water resources,planning and design of irrigation system,and reducing the ineffective water consumption of forest land.Taking Camellia oleifera forest in subtropical hilly region as the research object,this study adopted instruments and equipment such as Micro Lysimeter,LCI-SD portable photosynthesis meter,ETgage simulated evapotranspiration meter,combined with water balance method and Penman-Monteith model.To distinguish and quantify soil evaporation and plant transpiration in the subtropical hilly region,and to reveal and quantitatively explore the characteristics of evapotranspiration and its response mechanism with influencing factors,to explore the internal relationship between evapotranspiration（E）,evapotranspiration（T）and evapotranspiration,and to verify the applicability of Penman-Monteith model in this region.The following achievements have been made:（1）The characteristics of soil evaporation in Camellia oleifera forest in subtropical hilly region were quantified and analyzed.From April to September 2019,the total soil evaporation of Camellia oleifera forest in subtropical hilly region was about 192.15 mm,with a daily average of 1.05 mm.The average daily soil evapotranspiration at spring,summer and autumn stages was 1.11,1.15 and 0.89 mm/d.The relationship between soil evaporation and influencing factors was explored,and the characteristics of soil evaporation in different spatial locations were defined.There was a significant positive correlation between soil evaporation and soil water content in 5 cm soil layer at summer and autumn shoot stages.Therefore,scientific measures should be taken to control the non-productive consumption of water in Camellia oleifera forest during the actual production.The regression equation of water surface evaporation and soil evaporation was obtained by fitting:E=0.79 E₀–0.004（R²=0.67**）,which provided a theoretical basis for the estimation of soil evaporation in Camellia oleifera forest in subtropical hilly region.（2）The transpiration characteristics of Camellia oleifera forest in subtropical hilly region were explored.During the experiment period,the diurnal variation trend of transpiration rate of Camellia oleifera in subtropical hilly area was"double peak"type.The average transpiration rate of Camellia oleifera was 1.94 mmol·m^-2s^-1in August and 1.37mmol·m^-2s^-1in September.The maximum is usually around 12:00 noon.During the test period,the average transpiration per plant was 6.37 mm/d in August and 4.39 mm/d in early September.The transpiration remained at a high level in August,indicating that Camellia oleifolia was in a state of high water consumption at this time,and more attention should be paid to water control of Camellia oleifolia.（3）The characteristics of evapotranspiration in subtropical hilly region were elucidated and quantified.In the experimental period（142d）of 2019 and 2020,the total reference evapotranspiration was 556.51 mm,and the actual evapotranspiration was 653.36 mm.In general,the ratio of total evaporation to total transpiration of Camellia oleifera forest is about 1:4,and the fitting equation of local evapotranspiration and actual evapotranspiration is ET=1.01 ET_gage+2.29（R²=0.83**）.In the future agricultural management,ETgage simulation evapotranspiration instrument can provide a theoretical basis for estimating the actual evapotranspiration of Camellia oleifera forest in subtropical hilly region and developing scientific irrigation system.