Effect And Mechanism Of Leaf Litter Decomposition In Mid-Subtropical China To Simulated N Deposition Addition

Through the controlling litter decomposition situ experiments have been conducted in the castanopsis carlesii natural forest at the field positioning observatory of Key Laboratory for Subtropical Mountain Ecology(the Ministry of Science and Technology and Fujian Province funded)and Key Laboratory of Geographic and Ecological Processes in Humid Subtropical Areas funded by the Ministry of Education.The 4 kinds of leaves litter of Castanopsis carlesii?Acacia confuse Merr?Tsoongiodendron odorum and Cunninghamia lanceolata have been choosed as the research objects.In order to study the effects of nitrogen deposition to the soil nutrient and the litter decomposition and nutrient release,the situ experiments have been performed as add N respectively as HN(15 g N·^-2·a^-1),MN(10 g N·^-2·a^-1),LN(5 g N·^-2·a^-1)and CK(0 g N·^-2·a^-1).The followings are presented the results of experiment:adding external source N to 1 a will decrease pH value of soil,increase enzymatic activity of ?G,CBH and AP of soil,and decrease enzymatic activity of PhOx and Perox.In the period of supervision of 2 a,the decomposition speed change trends of 4 types of litters are all fast early then slow later.The decomposition speed of soongiodendron odorum is fastest and the speeds of acacia confuse and firs are relatively slower.The results present that litter decomposition is influenced by other internal or external factors in addition of content of subtrate and the factors make the different change of decomposition speed and N content.The import of external resource N restrains the litter decomposition of 4 types of trees,but different type of tree responses in different way to external resource N.The reason of inhibiting effect is that enrichment of inorganic N hinders decomposition of lignin and cellulose.The main elements' releases are almost impeded by external resource N and different types of tree and different elements response differently to external resource N.In the period of supervision of 1 a,4 types of hydrolytic enzymes activities of 4 kinds of trees' litters are almost increasing early and decreasing later,and the peak value appears in the sixth to ninth month.As the 2 kinds of oxidase activities,except the Acacia confuse Merr confuse processed by MN and Castanopsis carlesii which increase early and decrease later,most increase early,then decrease and increase lastly.Basically,the highest enzymatic activity appears in the sixth month which presents 6 kinds of extracellular enzymatic activities are not only affected by nitrogen deposition,but also related with the condition change of rainfall and temperature in the research areas.