| Loess Plateau is one of the fragile environment. The economic development are restricted seriously by arid and water and soil run off. It has been proved that the revive and construct of plants in this region is the basic measure of water and soil conversation , environment construct and agriculture,forestry,stock raising . However, the contradictions among forests, plants and soil water are obviously in the process of plants revive because of water shortage, therefore ,how to utility the water and increase the cover rate of pants are the urgent thing we must be do.This article studied the laws of water physiological response , water use efficiency ,change of forest land soil water. Meanwhile , the proper irrigation lever in different precipitation ,gathering water areas and forestation density were determined. 1. Forests drought resistanceThe roots of Pinus tabulaeformis, Platycladus orientalis and Robinia pseudoacacia were wrapped by plastic film ,then the dry environment was made .The tests showed that the photosynthetic rate of P. orientalis was higher than that of P. tabulaeformis ,but the transpiration was opposite. After one year of treating ,photosynthetic rate of P. tabulaeformis reduced 55.1%,P. orientalis 45.6%, R. pseudoacacia 56.2%.In water use efficiency , P. orientalis was higher about 40% than that of P. tabulaeformis.The leaf amounts of P. tabulaeformis, P. orientalis, R. pseudoacacia were 76.1%,81.7% and 78.5% of control. Two years later ,they were 55.2%,61.6%,23.8%, and leaf areas of R. pseudoacacia were 75% of control. The lengths of branch of P. tabulaeformis and P. orientalis were 64.3% and 66.7% of control respectively after one year , and they were 37.8% and 46.1% after two years. It was showed that the drought resistance among three trees were different , P. orientalis was strongest, then wes P. tabulaeformis , the third was R. pseudoacacia. 2.Characteristic of forestry biologic response in different conditions of waterP. tabulaeformis , P. orientalis and R. pseudoacacia were treated by supporting 1.5 ,1.0, 0.5 times of precipitation and formed soil water steps .It was showed that the net photosynthetic rate of P. tabulaeformis, P. orientalis , R. pseudoacacia increased 60.2%,63.3%,25.0%;63.5%,27.9%,5.1% and 57.7%,27.0%,4.9% than that of control respectively in treating of 1.5,1.0,0.5 times precipitation . The change of photosynthetic rate and transpiration rate appeared two peaks .In growing seasons ,the average transpiration rate of P. tabulaeformis, P.orientalis,R.pseudoacaciawere0.4i6*10-4,0.383*10-4,0.345*10-4,0.308*10-4mol g-1s-1;0.352*10-4,0.322*10-4,0.302*10-4,0.227*10-4molg-1s-1; 0.009,0.009, 0.008, 0.007molm-2s-1 in 1.5,1.0,0.5 times and control. The transpiration rate of P.tabulaeformis related to the soil water intensity of illumination and air temperature . The test showed that the leaf water potential raise with soil water increased ,and the leaf water potential of P. tabulaeformis was higher than that of P.orientalis.3. Characteristic of soil water of forest land and proper irrigation leverThe change lows of forest land soil water were studied. When the precipitation was normal ,total soil water of man-made forest of P. tabulaeformis and R. pseudoacacia were stable in different years. In the situation of 1.5,1.0,0.5 times and control , the total saving water of P. tabulaeformis were 298.1,272.2,253.6,206.6 mm respectively , P. orientalis were 334.3,276.9,261.8,247.8 mm respectively in 4-10 month, R. pseudoacacia were 268.9,236.6,199.2,182.9 mm respectively in 5-10 month which were lower 9.8%,13.1%,21.2%,19.4% than that of R tabulaeformis, lower 14.4%,16.1%,30.9%,25.2% than that of P. orientalis. In this region , soil water could permeate to 1.2m in different water treating ,and there was a most wet layer under 0.4-1 .Om. Meanwhile ,the total water of expend directed to water support lever ,which of R tabulaeformis were 1036.0,893.6,645.6,469.4 mm , P. orientalis were 959.8,797.1,647.1,455.5mm in 1.5,1.0,0.5 times and control respectively in 5-10...
|
PDF Full Text Request