N mineralization and nitrification in a primary Lithocarpus xylocarpus forest and degraded vegetation in the Ailao Mountain, Yunnan Province

Using the closed-top tube incubation method, we examined the soil nitrogen (N) mineralization and nitrification in the primary Lithocarpus xylocarpus forest, a secondary oak forest and a tea plantation in the Ailao Mountain, Yunnan Province, China. This study was conducted in the dry season from November 20, 1998 to May 15, 1999. Results showed that there were significant differences among the three vegetation types in both net N mineralization and nitrification rates, and they also demonstrated temporal variation. The net ammonification rate (RA) was much higher than net nitrification rate (RN), and the latter was about 0.5%-10% of the former. Our results indicated that incubation period, vegetation type and the location of plot all interactively affected RA, RN and net mineralization rate (RM ). We provided evidence that anthropogenic disturbances could result in changes of ecosystems processes such as N mineralization and nitrification rates. It is obvious that tea plantation and secondary growth forest have more physically (mainly temperature and moisture) controlled N transformation processes than the well-preserved primary L. xylocarpus forest, implying that the conservation of primary forest ecosystems in the Ailao Mountain region should be emphasized.