Nutr ient Character istics of Stem-Flow in D ifferentTree Spec ies in M iddle Subtropics

The concentrations of 9 nutrient elements (N、P、K、Ca、Mg、Cu、Zn、Mn、SiO2 ) in stem-flow, and rainfallwere measured in 22～25 years old Cinnam om um cam phora, Pinus taeda, Quercus a liena,M ichelia m acclurei from Ap ril of 2003 to July of 2004 at Zhuzhou. The results showed: the concentrations of the nutrients in rainfall varied according to the month; The concentration sequence of the nutrient elements in p recip itation were follows: Ca >NH4-N > SiO2 > Zn > K >NO3-N >Mg > Fe >Mn > P > Cu; The concentrations of the nutrients in stem-flow also variedin the same way and changed seasonally. Compared with that in p recip itation, most of them increased; The nutrientcharacteristics of stem-flow for different tree species differed significantly and the concentration sequence of the totalnutrient elements in stem-flow were follows: Pinus taeda, Quercus aliena、Cinnam om um cam phora, M ichelia m acclurei; Proportion of nutrient in stem-flow of different nutrient elements also differed significantly among all nutrientsanalysed. It was found that the highest concentration was for NH4-N, Ca, K, SiO2 , middle forMg,NO3-N, Zn,Mn,and the lowest for P, Fe, Cu; Compared with atmospheric p recip itation, the stem2flow of four tree species togetherperformance were, the concentration of Cu nearly did not change, other element content had a bigger change, Cinnam om um cam phora stem-flow Zn, SiO2 , Fe, Cu; Pinus taeda, Quercus aliena stem-flow Zn, Fe; M ichelia m acclureistem-flow Zn were lower than those in p recip itation, significant variation was especially noted for Zn in the four treespecies