Studies On The Water Transpiration Of Two Main Afforesting Plants On Sandy Land In Yanchi

Water is the limiting factors of revegetation and ecological construction in arid and semi-arid regions,so the thesis mainly aimed at the issues about soil water bearing capacity of vegetation cover.According to the theory of soil-plant-atmosphere continuum,the paper studied the water consumption characteristics,forest stand water consumption rules,water consumptive using and water requirement of the forest land and actual evapotranspiration of the forest land about single plant of shrub species Caragana spp.and main arbor species Ulmus pumila.And at the same time the water consumption rule of the Caragana spp.and Ulmus pumila forest land was researched. Main research as followings:In growing season(May to September),the research found that at the continuous observation of water consumption about the single plant of salt pond and sandlot Ulmus pumila and Caragana spp.,daily average water consumption of the former plant is 16.3L/d,the latter one is 2.13 L/d. The diurnal variation rhythm of sap flow is basically coincident,at 7:00 it notable increases,at 9:00 the peak appear and it will keep a high value at 8:00～18:00,after 18:00 it's drop rapidly,till 20:30 it's drop utmost and will continue all the night.The sequence of environmental factors in which the influence to Ulmus pumila and Caragana spp.are solar radiation＞relative air humidity＞air temperature＞wind speed.The multiple linear regression equation between sap flow and environmental factors are derived.V_{Ulmus pumila}=0.691R_e+76.936T+11.271H_a-1700.242 (R²=0.804),V_{Caragana spp.}=0.077R_e+9.442T+6.954V_s+0.747H_a-172.372(R²=0.814)By using the actual measurement date,the above equation was been validated.The average errors are all less than 10%,that means the calculation accuracy is reliable.Utilizing sapwood area and leaf area as space absolute amount.According to the above formulas,the estimation value of water consumption in growing season(May to September) about all the shelter forest stand of Ulmus pumila and Caragana spp.are 31.13mm,64.14 mm,42.63 mm,33.92 mm,13.24 mm and 21.72 mm,36.58 mm35.37 mm,28.12 mm,17.19 mm.The soil water vertical distribution of Ulmus pumila and Caragana spp.sample plots have clearly layered characteristics.They have three layers:low value layer,active layer and relative stabilization layer.And three stages in accordance with seasons:weekly water loss stage on May, consumption stage on June to August and slowly recovery stage on September.In 2007 the rainfall got the normal level and have surplus,and the surplus of sample plots of Ulmus pumila and Caragana spp.are 5.64mm and 2.2mm.