Difference of daily understory evapotranspiration under two water conditions in Larix principis-rupprechtii plantation
[Objective]The purpose of this study is to explore the impact of soil moisture on the daily understory evapotranspiration in Larix principis-rupprechtii plantation,so as to provide a theoretical basis for understanding the mechanism of forest evapotranspiration adapting to climate change and developing plans for coordinated forest water management.[Method]Taking L.principis-rupprechtii plantation in Diediegou small watershed in semi-arid area of Liupan Mountain in Ningxia as the research object,two experiments(blocking precipitation or water-proof input,and natural precipitation input)were conducted.Soil moisture gradient was artificially increased,and the effects of environmental factors(air temperature,solar radiation intensity,precipitation,and so on)on the daily understory evapotranspiration under the two soil moisture conditions were analyzed.[Result]The daily understory evapotranspiration in August,September and October under natural precipitation condition was 67.06,36.32 and 29.49 mm·d-1,respectively,which was greater than that under water-proof treatment(54.22,20.07,and 11.35 mm·d-1).The daily understory evapotranspiration under the two water conditions was characterized by a gradual decrease,and the fluctuations under natural condition was greater than those under water-proof treatment.From August to October,the difference in daily understory evapotranspiration under both water conditions generally showed a wavy pattern of first increasing and then decreasing,while the ratio showed a gradually increasing wavy pattern.In August,September and October,the mean difference between natural evapotranspiration and water-proof evapotranspiration was 0.41,0.54 and 0.59 mm·d-1,respectively,with ratios of 1.29,1.91 and 2.74,respectively.As the potential evapotranspiration increased,the ratio of daily evapotranspiration difference to soil volumetric water difference under both water conditions gradually increased.The effect of soil moisture on understory evapotranspiration was small when the daily potential evapotranspiration was less than 3 mm·d-1,but increased when the daily potential evapotranspiration was more than 3 mm·d-1,and increased significantly when the daily potential evapotranspiration was more than 5 mm·d-1.[Conclusion]The factors affecting daily understory evapotranspiration are roughly the same under both water conditions.The difference lies in that the daily understory evapotranspiration under natural condition is more affected by precipitation,while that under waterproof treatment is more affected by soil moisture.Future study should focus on the influence of multiple soil moisture gradients on understory evapotranspiration difference.[Ch,7 fig.1 tab.28 ref.]
water conditionunderstory evapotranspirationLarix principis-rupprechtii plantationsemi-arid region
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