Effects Of Fertilization On Ecophysiological Indicators And Xylem Embolism Of Four Tree Species

2-year-old well-growth Robinia pseudoacacia L., Ligustrum lucidum Ait., Acer truncatum Bge. and Ulmus pumila L. seedlings were used as research material, both water control and fertilization treatments were applied for this research. Then a series of ecophysiological indicators of the four tree species, including twig water potential, loss of hydraulic conductivity, stomatal conductance, net photosynthetic rate, transpiration rate were measured. The results showed as follows:Under the normal moisture condition, as the amount of nitrogen fertilizer increased the twig water potential, loss of hydraulic conductivity, stomatal conductance, net photosynthetic rate, transpiration rate and water use efficiency of R. pseudoacacia, L. lucidum, A. truncatum and U. pumila augmented, the loss of hydraulic conductivity decreased; under the moisture stress condition, with the amount of nitrogen increased, the twig water potential, loss of hydraulic conductivity, stomatal conductance, net photosynthetic rate, transpiration rate and water use efficiency decreased, loss of hydraulic conductivity augmented. The results illustrated that, under the normal moisture condition, the application of nitrogen fertilizer was conducive to the growth and accumulation of photosynthetic products of the plants; and under moisture stress situation, the ecological indicators were regulated by reducing stomatal conductance, with the xylem embolization increased and transpiration reducted, which played a drought-resistance role by restricting sap flow. The humic acid had the same function. Application of nitrogenous fertilizer induced to plant drought-resistence because under the moisture stress condition, the form of xylem embolism decreased the xylem and twig water protentials, the stomata shuted to diminish the transpiration, and the plant water use efficency improved.The results of the regression analysis between the xylem embolization and the ecological indicators idicated that drought-resistance by restricting sap flow in the xylem is a complex ecophysiological process, and was related to unique ecophysiological indicators under different moisture control and fertilization conditions.Under different moisture and fertilization treatments, the level of xylem embolism of the four species are different, among the four tree species, the U. pumila had the biggest xylem embolism under all conditions, the results showed that, the the U. pumila had the biggest droght-resistance ability.