| Being one of the main afforestation tree species in Liupan Mountain,Larix principis-rupprechtii plantation plays an important role on water conservation and timber production.To elucidate the variation of the sap flow velocity(Js)among different slope positions and the relation between environmental factors and sap flow,continuous monitors of the sap flow velocity changing in different slope positions were started in the growing season of the year of 2016,the results shows that:The cyclical variation of meteorological factors was being observed obviously,variation of solar radiation is very large,the response of soil moisture to rainfall is obvious,the soil water content increases rapidly during the process of precipitation input,and decreases gently during the drought period,the response of the soil temperature on upper slope and middle slope to the air temperature has 8 hours lag.There is a parabola change of the daily solar radiation and the daily air temperature,both of them reached a peak in the middle of the growing season,then decresed in the rest of time.The soil water content decresed continuously during the whole growing season due to the increasing transpiration and the decreasing precipitation.The trend of the Js of three slopes are consistent,but have differences in the start and stop time.Relatively speaking,the sap flow started early and end late in middle slope,which also has a higher peak value.The order of the average value of Js in the whole growing season is:middle slope(0.0474)>upper slope(0.0384)>lower slope(0.0370),the Js of middle slope is significantly greater than other slope positions in August and September.Js does not have regular volatility in daily scale,in the early and middle stage of growing season,the daily Js has a large fluctuation.In the monthly scale,the Js value reached a peak in June on three slope positions,then decreased gently till the end of the growing season.Pearson correlation analysis revealed that Js is significantly correlated with the environmental factors(except wind speed)during the growing season,the solar radiation,VPD and relative humidity have the largest correlation coefficient.Regression analysis between Js and environmental factors showed that environmental factor’s filtering into regression equation changed with different slope positions,solar radiation,air temperature and soil water content are the main influencing factors of the upper and lower slope’s Js,while the solar radiation and air temperature are the main influencing factors of the middle slope’s Js.Prediction model fitting well in all slope positions and the determination coefficients were above 0.6.Pearson correlation analysis between Js and environmental factors in monthly scale revealed that the variation of the R2 are much alike among different slope positions,the R2 of Js to solar radiation is higher at the beginning and ending stage of the growing season,and the R2 of soil water content increased in August due to the absence of precipitation in this month.The K value of soil water content is higher on upper slope,which indicated that mild water stress occurred on upper slope in growing season.To estimate the Js of the Larix principis-rupprechtii plantation on the study slope precisely,at least 15 or 13 trees are required if the error of the measured Js should be controlled within 10%under confidence level of 95%or 90%.At least 19 or 18 trees are required when the error of the measured Js should be controlled within 5%under confidence level of 95%or 90%. |
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