Abstract: Using the buried-bag method we measured nitrification and net N mineralization rates for soils (0～10cm) under a variety of forest types in Xishuangbanna, Southwest China in July of 1998. The forest types studied were: tropical seasonal rainforest, Melettia leptobotrya secondary forest, forest gap, and slash-and-burn agricultural land. Net N mineralization rates were 6.55 mg N·kg-1· 30d-1 in seasonal rainforest and 6.37 mg N·kg-1·30d-1 in secondary forest. Nitrification rates were 16.28 mg N·kg-1·30d-1 in seasonal rainforest, 16. 38 mg N·kg-1·30d-1 in secondary forest. Nitrification and net N mineralization rates were –2.78 mg N·kg-1·30d-1 and –7.85 mgN·kg-1·30d-1 in forest gap , –3.69mgN·kg-1·30d-1and –10.69mgN·kg-1·30d-1 in agricultural land, respectively. Ammonification rates were negative in all the studied sites, with the result that net N mineralization rates were lower than nitrification rates.

Key words: Tropical rainforest, Secondary forest, Forest gap, N mineralization, Nitrification, Ammonification