| Forest and water was interaction and mutual influence.Under the background of global water shortage,to realize the sustainable utilization of water resources,we must fully understand the water cycle mechanism of each link of forest.In this paper,we study the evapotranspiration features of rubber plantation.Research area is located in the third testing site of Chinese Academy of Tropical Agricultural Sciences institute.Using eddy covariance system to observe the water vapor transmission characteristics of different age rubber plantations in a long term.Comparative study water vapor transmission and transpiration characteristics of different age rubber plantations on different time scales.Used the methods of hydrologic budget and BREB and Penman-Monteith to estimate the evaporation of adult rubber plantation and compared with eddy covariance(EC).The purpose of this study is to fully understand the evapotranspiration water features of the rubber plantation in different growth stages on different time scales,and to find out the main environmental factors affecting evapotranspiration,and to find the right evapotranspiration method of rubber plantation.The results of the study are as follows:(1)The overall trend change characteristic curve were similar of the net radiation flux(Rn),soil heat flux(G),latent heat flux(LE)and sensible heat flux(H)of rubber plantation,and they were all unimodal type change,and increased first and then reduced during the day,and basic remained unchanged at night.But the change of H and LE curve were rough.The energy distribution characteristics of rubber plantation were shown as:Rn>LE>H>G>S.Energy component of different season was different,LE was larger than H in rainy season.and in dry season the difference was little.The energy distribution of different age rubber plantations was different.(2)The energy closure results of rubber plantation were as follows:on the half an hour scale,energy closure of adult rubber plantation in rainy season and dry season and throughout the year were 76.07%,66.91%and 73.02%;Energy closure of young rubber plantation in rainy season and dry season and throughout the year were 91.88%and 89.62%and 90.96%.On the day scale,energy closure of adult rubber plantation in rainy season and dry season and throughout the year were 91.42%and 75.27%and 85.18%;Energy closure of young rubber plantation in rainy season and dry season and throughout the year were 92.16%and 94.20%and 92.82%.On the month scale,energy closure of adult rubber plantation was 89.75%,energy closure of young rubber plantation was 93.33%.(3)The diurnal water vapor flux variation characteristics of rubber plantation was the inverted "U" type.The water vapor flux are near zero at night,and basic remained unchanged.And during the day,it was increased first and then reduced,and the maximum value around 12:00～13:00.The the vapor flux in rainy season was greater than the dry season,and the maximum value appeared earlier.The water vapor flux were positively correlated with net radiation(Rn),air temperature(Ta),vapor pressure deficit(VPD).The result of polynomial regression analysis was as follows:Water vapor flux and Rn coefficient of correlation,the adult forest and young forest in rainy season respectively were as follow:R~2=0.5856,R~2=0.7330,and in dry season respectively were as follow:R~2=0.3466,R~2=0.4004;Water vapor flux and Ta coefficient of correlation,the adult forest and young forest in rainy season respectively were as follow:R~2=0.4733,R~2=0.5212,and in dry season respectively were as follow:R~2=0.2723,R~2=0.2772;Water vapor flux and VPD coefficient of correlation,the adult forest and young forest in rainy season respectively were as follow:R~2=0.4560,R~2=0.5315,and in dry season respectively were as follow:R~2=0.2224,R~2=0.2541.The reslut of many factor correlation analysis was that,the main environmental factors which affectied the water vapor flux of rubber plantation were net radiation(Rn),vapor pressure deficit(VPD),air temperature(Ta),volume water content(VWC),soil heat flux(G),weed speed(Ws).But the main factors were difference in different age forests and in different season.(4)The diurnal evaporation in a year was unimodal type change.The averages of the diurnal evapotranspiration of adult forest and young forest were 1.45mm and 1.93mm.The diurnal evapotranspiration in rainy season was greater than in dry season,the adult forest and young forest diurnal evapotranspiration in rainy season were 3.69mm and 3.94mm,in dry season were 2.60mm and 3.04mm.The month evapotranspiration of same month were different in 2013 and in 2014.On the year scale,evapotranspiration of rubber plantation was greater than precipitation.In 2013,the precipitation was 1582.4mm,and the evapotranspiration of adult and young rubber plantation were 949.7mm and 1039.2mm,and the accounts for the proportion of precipitation were 60.0%and 65.7%;In 2013,the precipitation was 2243.5mm,and the evapotranspiration of adult and young rubber plantation were 929.0mm and 1108.3mm,and the accounts for the proportion of precipitation were 41.4%and 49.4%.(5)Evapotranspiration of rubber plantation were positive correlation with Rn and VPD.As temperatures rise evapotranspiration of rubber plantation was increased first then decreased.And VWC was one of the factors that affected the evapotranspiration of rubber plantation.Many factor correlation analysis results were as follows.On the day scale,the main environmental factors that affected evapotranspiration of the adult rubber plantation were Ta,VWC,VPD and Rn,but the main factors were Rn and Ta on the month scale.In the young rubber plantation,the main environmental factors which affected evapotranspiration were Ta,Rn,VWC and VPD on the day scale,but on the month scale,the main factors were Rn,Ta and VWC.(6)The evapotranspiration of adult rubber plantation in 2014 was measured by different methods,and compared the results of different methods.The evapotranspira-tion was 928.97mm that measured by EC,and the result of hydrologic budget was 1168.03mm,and the evapotranspiration which measured by hydrologic budget was 25%higher than the EC.The evapotranspiration was 1376.7mm that measured by BREB,and the result of Penman-Monteith was twice the EC. |
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