Transpiration Characteristics Of Main Trees Seedlings Of Urban Forest On The Loess Plateau

Urban forest is an important branch in China forest reconstruction area and drought is the bottle-neck for environment restoration and urban forest construction. People have paid much attention on soil drying and afforestation failure caused by tree species improper selection. As a key moisture parameter, potential consuming capacity of plants is reflected by transpiration rate and been studied by some people. Theoretic guides for tree species selected, proper arrangement and perfect manual vegetation system reconstruction will be provided by study on traits of tree species drought-resistance.Based on potted plant, instantaneous balance, Licor-6400 and precious electric balance(TC30K), relationship between transpiration rate and water consumption rate, transpiration rate and environmental factors of popular seedlings on loess plateau, such as Robinia pseudoacacia, Amorpha fruticosa, Amygdalus vulgaris, Ulmus pamila, Rhus typhina,Pinus tabulaeformis,Platycladus orientalis, Sabina vulgaris, P. nigra var. austriaca and P. ponderosa,etal, has been studied in their growth seasons (May to October) under natural conditions.The result showed as following. Daily curves of water consumption rate of tested tree species changed with sole or double peaks. And all daily curves with sole peak for all trees in September and October, for broad-leaves trees also in May. Daily curve of Amorpha fruticosa,Ulmus pamila and Rhus typhina was sole peak, trend of their daily fluctuating was same and differences among their water consumption capacity increased in July. Daily curve of Amygdalus vulgaris was double peaks and its moisture consumption rate was the highest among all broadleaf seedlings. Amygdalus vulgaris maintained its water balance by its strong capacity of moisture utilizing and water restoration in its leaves. Other broadleaf seedlings maintained their water balance by their low moisture consumption rate. In conifers, Daily curve of Sabina vulgaris was sole peak and the value of peak was most. Other daily curves were sole peak. Value of peak of P. nigra var. austriaca was least. Fluctuating range of P. ponderosa and P. nigra var. austriaca were both narrow and their capacity of environment adaptation and moisture restoration were stronger. Moisture consumption trend of seedlings were more significant in August.The order of average rate of water consumption is Amygdalus vulgaris,Sabina vulgaris,Amorpha fruticosa,Robinia pseudoacacia,Rhus typhina ,Platycladus orientalis,P. nigra var. austriaca,Pinus tabulaeformis, Ulmus pamila, P. ponderosa from higher to lower for all tested trees. And the average value of broad-leaved trees was 0.0639 kg.h^-1 which washigher than of coniferous trees ( 0.0570 kg.h'1 ). Time which the highest water consumption of Rhus typhina and P. ponderosa appeared was in Juny, Amygdalus vulgaris and Platycladus orientalis in July, Pinus tabulaeformis and Sabina vulgaris in August. The best time and the fairest irrigation water quantity would be decided according to water consumption of every tree species.Environments factor such as sun radiation, atmospheric humidity, atmospheric temperature, etc. had influenced transpiration of every tree. And the key factor for a tree was different from other trees, and a factor's importance changed in different growing period of a tree or in different trees. These was not only the performance of changing of the key factor or the dominating factors caused by the outsider environment variety, but the complexity and the difference which tree's transpiration respond to environment.The average stomatal conductivity of Amorpha fruticosa is 0.0327 mmol/s.m2 of in May, July and August, and Amygdalus vulgarises was 0.0963 mmol/s.m2, Rhus typhina's was 0.1753 mmol/s.m2, Robinia pseudoacacia's 0.0483 mmol/s.m2, Ulmus pamila's 0.085 mmol/s.m2. Transpiration rate of a tree was higher if its stomatal conductivity was higher, too was Whereas in the ordinary, but the transpiration rate did not always rise with the stomatal conductivity's increasing. The relationship of them was linear function relation or logarithmic function relation for some trees, or a adverse linear function for some trees in little times.Transpiration rate, used to express the potential ability, and water consumption rate to the facture ability of water consumption for trees, but it would got a different result when expressing characteristic of water consumption for a tree using another index. The average value of water transpiration rate for Amorpha fruticosa and Robinia pseudoacacia was the highest and the lowest, and of water consumption rate for Amorpha fruticosa and Rhus typhina especially among the broad-leaved trees in May. Amygdalus vulgarises rate and Ulmus . pamila's rate of water consumption were the highest and the lowest especially in July and in August. The highest and the lowest value of transpiration rate were of Rhus typhina and Robinia pseudoacacia in July, of Ulmus pamila and Amorpha fruticosa in August separately. As indexes to express character of trees, transpiration rate can be used to compare the character of water consumption for tree, and water consumption rate to measure facture ability of water consumption of tree seedling.