Study On Key Evapotranspiration Features Of Two Vegetation Types In Diediegou Watershed Of Liupan Mountains

We studied the evapotranspiration characteristics in growing season of Larix principis-rupprechtii forests and natural grassland in Semi-arid area of Liupan Mounains.We analyzed the sapflow under different weather conditions and sample trees in experimental plots. The study evaluated the impact of early autumn snowfall to sapflow rate We analyzed differences of the growing season evapotranspiration on different grassland slope positions. Explores the changes of aboveground biomass and other hydrological factors on the slope. The results were shown in below.(1) Total rainfall was 613.15 mm in the 2014 growing season. In Larix principis-rupprechtii forests plots, precipitation mainly consumed by vegetation evapotranspiration. Total evapotranspiration was 552.18 millimeter, including under forest evapotranspiration 317.76 millimeter(57.54% of the total evapotranspiration). Trees transpiration was 186.4 millimeter(33.7% of the total evapotranspiration). Canopy interception was 48.3 millimeter(8.76% of total evapotranspiration). Stand evapotranspiration and its components have significant changes in the month, reaching a maximum in mid-growing season(7-8 months),and the end of the growing season reduced.(2) The presence of individual trees within Larch plantation transpiration had big difference, such as sapflow rate was affected by DBH. Diameter larger sample tree(No. 221 sample trees, diameter 15.6 cm) on July 5 the maximum daily flow rate of the flow rate(0.31 ml·cm-2.min-1) is greater than the diameter smaller sample tree(No. 47 sample trees, diameter 13.9cm) maximum(0.24 ml·cm-2.min-1), 29.1% of the former than the latter large. The sap flow rate of two trees reached the maximum at same time. This indicates that the sapflow is a common phenomenon in the trees physiological activities. Tree transpiration related with tree-related factors and dominance.(3) Study area suffered a long lost early snow in 2011 autumn. Observations found that the rate of the snow day(Sep. 18th) has lower peak(0.011 ml·cm-2.min-1) and transpiration(0.23 mm) than typical sunny at Sep 15th(0.167 ml·cm-2.min-1,0.84 mm). But the typical rain Sep.16th(0.013 ml·cm-2.min-1,0.22 mm) and snow had same level sapflow rate. Sap flow rate had been some recovery after the snow with the temperature rising. Analysis showed that under sunny, rainy and snowy sap flow rate was positively correlated with air temperature, solar radiation and vapor pressure, was negatively correlated with the relative humidity.(4) Evapotranspiration had differences on semi-sunny slope position on six plots of natural grass slope.The evapotranspiration(mm) of six plots was 411.4(Top),361.0(Upper),394.8(Middle-upper),365.0(Middle-down),422.7(Down), 365.9(Foot) in 2014 growing season. Evapotranspiration shown obvious wave change.(5)Aboveground biomass of semi-sunny natural grasslands slope have significant differences with slope position. The aboveground biomass(t / hm2) of six plots was 3.15(Top),2.86(Upper), 5.16(Middle-upper), 5.02(Middle-down), 3.6(Down), 3.21(Foot). The maximum biomass of plot was the Middle-upper plot. Aboveground biomass had spatial scale effect on the slopes. The moving average of aboveground biomass(Y) on slope followed the leaving top of the hill with the absolute horizontal distance(X,m) non-linear changes in their relationship as Y=-1×10-7X3-9× 10-6X2+ 1.54×10-4X+2.7775(R2=0.8204).