哀牢山木果柯林及退化植被下土壤氮素矿化和硝化作用

采用封顶埋管法,我们于11月21日至次年4月15日,分3个培养期共165天(包括干季初期、中期和末期),对哀牢山原生木果柯林(Lithocarpusxylocarpusforest)、栎类次生林(secondary oakforest)和人工茶叶地(teaplantation)三种群落类型的土壤氮素矿化和硝化作用进行了研究.结果表明:在3个培养期中,不同群落下土壤的氮素矿化和硝化作用都具有明显差异;而且它们均具有明显的干季动态,但变化趋势不尽相同.净氨化速率远高于净硝化速率,后者约为前者的0.5%～10%.结果表明,培养期、群落类型和样方诸因子对净氮矿化速率和净硝化速率的影响均存在不同程度的交互作用.人为干扰能导致氮素矿化和硝化速率等生态系统过程的变化,我们的研究结果为此提供了证据支持.与木果柯原始林相比,茶地和次生林的氮素转化过程更多地受物理因素的控制(如温度和水分).这意味着哀牢山地区的木果柯原始林的保护应该受到重视.

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 (R_A) was much higher than net nitrification rate (R_N), 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 R_A, R_N and net mineralization rate (R_M ). 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.