The Effect of the Supporting Water on the Characteristics of Forest Biologic Response

Plants of Pinus tabulaeformis,Platycladus orientalis and Robinia pseudoacacia were irrigated by supporting 1.5,1.0,0.5 times of precipitation to form soil water steps.It was showed that the net photosynthetic rate of P.tabulaeformis,P.orientalis,R.pseudoacacia was increased by 60.2%,63.3%,25.0% and 63.5%,27.9%,5.1% and 57.7%,27.0%,4.9% than those of controls respectively in treating of 1.5,1.0,0.5 times precipitation.The change of photosynthetic rates and transpiration rates appeared two peaks.In growing season,the average transpiration rates of P.tabulaeformis,P.orientalis,R.pseudoacacia are 0.416×10^-4,0.383×10^-4,0.345×10^-4,0.308×10^-4 mol/g·s;0.352×10^-4,0.322×10^-4,0.302×10^-4,0.227×10^-4 mol/g·s;0.009,0.009,0.008,0.007 mol/m²·s in 1.5,1.0,0.5 times and control.The test showed that the leaf water potential increased along with the soil water,and the leaf water potential of P.tabulaeformis was higher than that of P.orientalis.