Abstract: The seasonal variation and export rate of N and P contents in leaves and the export course of N and P in decrepit leaves of 23 nitrogen-fixing and non nitrogen-fixing tree species were studied. The results showed that in the leaves of all tested trees, there was an obvious seasonal variation of N and P contents,their average variation rate was 21～23%,and the maximum appeared at decrepit stage. During this stage, the dynamic character of N and P in leaves was different between nitrogen-fixing and non nitrogen-fixing trees. The former displayed a low export rate, and the N content in their fallen leaves was 1.6～3.7 times higher than the later. The N content in the leaves of nitrogen-fixing trees was about 2.5% in growing seasons.

Key words: Nitrogen-fixing trees, N and P content, Nutrient dynamics, Mixed forest, isotopic composition, nitrate, ammonium