Study On Transpiration Characteristics Of Major Tree Species For Soil And Water Conservation In Loess Plateau Of Western Shanxi

Amiming at water consumption of trees construction and the using of water resources, for the purpose of investigating the ability of drought tolerance and water use efficiency of the trees planted in the Loess Plateau to adapt to arid environments, daily and seasonal changes of potential atmospheric evaporation in Loess Plateau and the sap flow velocity of4kinds of trees species for soil protecting in Semi-arid Area were studied by using the method of Thermal Dissipation Probe and semi-empirical formula from2009to2012. The water consumption of four stand in all seasons were estimated, and the correlation analysis between the Potential Atmospheric Evaporation and the sap flow velocity of4kinds of trees species were researched respectively, and based on which, the prediction model of the potential atmospheric evaporation and Sap flow velocity were created. The main results are as follows:1. The dynamic changes in the daily average of the sap flow velocity of Robinia pseudoacacia, Populus davidiana and Quercus liaotungensis are all the same as the dynamic changes of Potential Atmospheric Evaporation, and the diurnal variations of the sap flow velocity of them are also the same as one of Potential Atmospheric Evaporation, and the dynamic change of the sap flow velocity of Finus tabulaeformis is the same as one of Potential Atmospheric Evaporation in last spring, summer and early fall. However, the changes are different from the one of Potential Atmospheric Evaporation in other times. The dynamic change in the daily average of the sap flow velocity of Pinus tabulaeformis is all the same as the dynamic change of Potential Atmospheric Evaporation in spring, summer and fall, but winter. The sap flow velocity of Robinia pseudoacacia is the greatest among four trees in the last spring, summer and early fall, and the value, wave frequency and fluctuation range of the sap flow velocity of Pinus tabulaeformis are the greatest among four trees in winter.2. The values of the Potential Atmospheric Evaporation and the sap flow velocity of Robinia pseudoacacia, Populus davidiana and Quercus liaotungensis in sunny day are respectively higher than them in rainy day in spring, summer and fall, but winter. The value, the wave frequency and fluctuation range of the sap flow velocity of Pinus tabulaefonrmis in sunny day are the greater than them in rainy day in the whole year.3. In last spring, summer and early fall sunny days, the sap flow velocity of four trees increase rapidly from7:00to10:00, and reach a peak and stable on that value from10:00to13:00and sometimes midday depression phenomenon may be appeared, then it goes down, and stable on the bottom value from18:00to13:00. In last spring, summer and early fall shower days, the time when the sap flow velocity of four trees increase rapidly and reach peak all delay for1～2hours than sunny days. In last spring, summer and early fall days nearly without solar radiation, the diurnal variations of the sap flow velocity of four trees have no obvious day and night variations. There is a certain sap flow velocity in night and stable at a relatively low level for four trees in last spring, summer and early fall days. In last fall, winter and early spring sunny days, the diurnal variations of the sap flow velocity of four trees characterize by irregular curve and there is a certain sap (low velocity in night and stable at a relatively high level.4. The distribution of the monthly average value of the sap flow velocity of four trees during the year are basically the same from2009to2012, and all peak in June. The peak of the sap flow velocity of four trees from big to small was Robinia pseudoacacia, Populus davidiana, Pinus tahulaeformis and Ouercus liaotungensis, and fluctuating margin of the sap flow velocity of four trees from big to small was Robinia pseudoacacia, Populus davidiana,Quercus liaotungensis and Pinus tabulaeformis. The season average value of potential atmospheric evaporation and the sap flow velocity of four trees all show that:the mean value is the largest in summer, and least in winter, and the mean value in spring is more close to autumn, respectively. The most significant correlation between the sap flow velocity of four trees and the potential atmospheric evaporation have appeared in summer, and the worst in winter.and negative correlation between the sap flow velocity of four trees and the potential atmospheric evaporation have appeared in winter.5. The potential evaporation capacity are greater than precipitation in the whole year in the testing, respectively, and concludes that water shortage phenomenon exist all over years in the Loess Plateau. The gap between the potential evaporation capacity and the precipitation all show that:the largest in spring, and least in summer. And we can conclude that spring is the season when water shortage is most severe in the Loess Plateau.The transpiration water consumption of four trees is less than the potential evaporation capacity and the precipitation in the whole year in the testing. The transpiration water consumption of four trees from big to small was Robinia pseudoacacia, Firms tabulaeformis, Quercus liaotungensis and Populus davidiana, and the transpiration water consumption of Robinia pseudoacacia and Pinus tabulaeformis is obviously more than Quercus liaotungensis and Populus davidiana.