Study On Transpiration And Water Consumption Characteristics Of Artificial Robinia Pseudoacacia Forest In The Loess Plateau Of Eastern Gansu

This study takes the artificial Robinia pseudoacacia forest in the Zhonggou watershed of Jingchuan,in the Loess Plateau area of Eastern Gansu Province,as the research object and conducts in the growing season of May-October 2017.Various indexes such as SAP flow,trunk runoff,penetrating rain,soil(vegetation)evaporation under the forest and meteorological factors were synchronously measured.The study studied the relationship between the evapotranspiration of each component and total transpiration of the stand in the region,clarified the relationship between environmental factors and soil factors affecting sap flow at different growth stages and analyzed the relationship between night sap flow characteristics and driving factors of Robinia pseudoacacia was also understood.The results show that:(1)Variation of meteorological factors in growing seasonFrom May to October,the seasonal variations of various meteorological factors showed obvious seasonal differences,with the maximum monthly mean temperature of 25.15 C in July,the minimum relative humidity of 61.75% in July and the maximum relative humidity of 94.41%in October.The seasonal variations of solar radiation and saturated water vapor pressure were in keeping with that of temperature,and the maximum solar radiation and water vapor pressure in July were 250.00w/m and 1.46 kpa,respectively.Pa,the lowest solar radiation and water vapor pressure in October are 67.54w/m and 0.08 kpa,respectively.The seasonal differences of soil moisture content in different soil layers are different.Among which the soil moisture content in the surface layer of 5cm is the largest in May,followed by July,October,the smallest in May,the soil moisture content in the 5-80 cm layer is the smallest in May,the largest in October and the seasonal differences are significant.(2)Evapotranspiration of various components of Robinia pseudoacacia forestDuring the growing season of 2017,the total rainfall of Robinia pseudoacacia forest in Zhonggou watershed was 508.97 mm.Among the components of rainfall redistribution,the penetrating rain was 441.55 mm,the trunk runoff was 20.85 mm,and the canopy interception was 46.57 mm.The components accounted for 86.8%,20.85% and 46.57% of the redistribution of rainfall,respectively.Among which,penetrating rain accounts for the highest proportion of rainfall redistribution,followed by canopy interception,and trunk runoff accounts for the lowest proportion of rainfall redistribution.The evapotranspiration of each component of the stand was462.4 mm under the forest and 772.85 mm under the tree.The water consumption of tree transpiration accounted for 60.3% of the total evapotranspiration.The seasonal variation of evapotranspiration and total evapotranspiration of each component is the same,which increases first and then decreases.The evapotranspiration in July is the largest and that in October is the smallest.(3)Water Consumption of Tree Transpiration at Different Time ScalesDuring the whole growing season,the sap flow of tree trunks in different growing periods showed unimodal or bimodal changes in sunny days,and unimodal or bimodal changes in cloudy days,while the changes in rainy days had no regularity to follow;the daily mean value and peak value of sap flow in sunny days were larger than those in cloudy and rainy days;the start time,peak time and decline time of sap flow in different growing periods had significant seasonal differences.The sap flow usually starts at about 7:00 in the early growth stage and reaches its peak at about 13:00,which lags behind one hour in the middle growth stage.The sap flow starts at 6:00 in the peak growth stage and reaches its peak at 11:00-12:00,which is basically in line with that in the early growth stage.The factors affecting the sap flow change in different growth stages are different,but they are all different from air temperature,air temperature and air temperature.Solar radiation is significantly correlated with air humidity,and other influencing factors have different effects on sap flow with seasonal changes.regression models between sap flow rate and environmental factors at different growth stages were established by SPSS software.(4)Sap Flow Characteristics of Robinia pseudoacacia at NightDuring the whole growing season,the nocturnal fluid flow of Robinia pseudoacacia was obvious.The amplitude of fluid flow in the first half of the night was larger than that in the second half of the night,and that was larger in the sunny days compared with the rainy days,and gradually decreased with the alleviation of water deficit in the second half of the night,and increased with the increase of tree diameter at breast height.The environmental factors affecting the nocturnal water supply of Robinia pseudoacacia were water vapor pressure deficit,wind speed and soil moisture content within 40 cm.The regression models of DBH,tree height,crown width,Sapwood Thickness and nocturnal sapwood flow were established.The nocturnal sapwood flow was the combined effect of nocturnal transpiration and water deficit of supplementary daytime transpiration.The proportion of nocturnal water supply to total transpiration of Robinia pseudoacacia varied seasonally,with the monthly average contribution rates of 18.11%,5.82%,11.23%,8.61%,12.31% and 22.61% in the whole growing season.The contribution rate of night water supply to total transpiration of Robinia pseudoacacia was13.12%.