| Since the industrial revolution, human activities created a large number of active nitrogen, making atmospheric nitrogen deposition increased proportional. In addition to Europe and America, China has become the third-largest nitrogen deposition concentrated area. Excess nitrogen deposition has caused a series of ecological problems, such as:soil and water acidification, eutrophication, terrestrial ecosystems nitrogen saturation, nutrients imbalance and so on. Litterfall is an important part of nutrient cycling and energy flow in forest ecosystem, which in maintaining soil fertility, plant productivity, microbial activity and forest ecosystem carbon cycle have an important role.Therefore, under the background of globalization of nitrogen deposition, it is important to study the effects of nitrogen deposition on litterfall and nutrient dynamic. We selected camphor plantations as research subjects to simulated nitrogen deposition experiments in Hunan Forest Botanical Garden, setting four kinds of nitrogen added level of CK (Og N·m-2·a-1, control), LN (5g N-m-2·a-1, LN), MN (15g N·m-2·a（-1）,MN), HN (30g N·m-2·a-1, HN), study of nitrogen deposition on camphor forest litter amount, litter nutrient content, the return of the amount of elements and litter decomposition. The results showed that:（1）The annual litter amount of camphor plantations were4.53±0.32、3.95±0.28、3.56±0.4、4.46±0.48t·hm-2·a（-1） on the CK、LN、MN、HN levels, this could indicate that there was inbibitional effect of nitrogen deposition on litter amount. The seasonal dynamic was not changed with nitrogen fertilization. However, N treatments changed the monthly litter amount, from March to April, litter amount was the largest, LN treatment suppressed the amount of camphor forest litter, and HN performance role in promoting. A relatively large amount of litter from August to October, the nitrogen fertilizer treatments inhibited camphor forest litter amount, but in a relatively small amount of litter, LN、MN treatments performance role in promoting, HN treatments showed inhibition effect. Nitrogen treatments on branches, leaves litter mainly performance role in promoting, without effect to litter amount of fruit and debris.（2） After the nitrogen fertilization, the order of the nutrient content of litter were: C>N>Ca>K>Mg, where the carbon content did not change significantly, but with respect to CK treatment, LN, MN, HN treatments increased the nitrogen content of litter, indicating that the nitrogen content of each component of the litter response to nitrogen deposition sensitive. During the experiment, camphor plantations on nitrogen absorption rate decreases over time. N treatments increased K, Ca, Mg content of the litter, but the trend is not obvious. The components of litter C/N ratio has declined after N treatments （LN, MN, HN）, the average C/N ratio of branches, leaves and fruits decreased than CK treatment by37.22%,34.21%and35.57%,22.10%,22.65%and1.90%,28.15%,11.36%and12.61%, indicating the nitrogen content of litter obviously increased with the nitrogen fertilization, causing C/N ratio of litter decreased.（3） The order of the amount of elements returned were:C>N>Ca>K>Mg. N treatments inhibited the amount of C, Ca, Mg elements returned in litter, and promoted the amount of N elements returned. High nitrogen promoted the amount of K element returned, low nitrogen treatment inhibited the amount of K elements returned. In components of litter, the N treatments reduced the amount of carbon returned of branches and leaves. The treatments of LN and HN increased the amount of nitrogen returned of branches, and the treatment of MN showed a slight inhibition; The treatments of LN and MN increased the amount of nitrogen returned of leaves, and the treatment of HN showed a slight inhibition; The treatments of LN and HN increased the amount of C、N、K、Ca, Mg returned of fruits, and the treatment of MN showed a slight inhibition.（4） After the nitrogen fertilization, the dry weight residual rates of branches litter of camphor tree were:39.5%,35.9%,34.8%,37.8%the dry weight residual rates of leaves litter were:8.5%,9.8%,9.6%,9.1%, lower than the dry weight residual rate of branches litter significantly. In the natural state, leaves litter decomposition rate was greater than the branches litter significantly. N treatments promoted the decomposition rate of branches litter, decreased the decomposition rate of leaves litter, the difference between CK and LN, MN, HN treatments was not significant（P>0.05）. At the beginning of litter decomposition process, branches and leaves litter showed a slower decomposition rate. The decomposition rate is accelerated later. Last, the decomposition rate became gently. With the nitrogen fertilization （CK, LN, MN, HN）, the decomposition coefficient of branches litter were:0.830,1.090,1.085,1.075, turnover period were:3.609a,2.748a,2.761a,2.787a, Nitrogen treatments increased the decomposition rate on branches litter. The decomposition coefficient of leaves litter was: 1.783,1.694,1.806,1.838, turnover period were:1.723a,1.768a,1.659a,1.630a, the treatments of MN and HN increased the decomposition rate of leaves, and the treatment of LN showed a slight inhibition.（5）The C elements of branches and leaves were released in the decomposition process, the nitrogen fertilization did not have a significant impact on C content of branches and leaves. At the beginning of litter decomposition process, the C element content of branches and leaves has been reduced, the C element net release rate of branches litter was fluctuated downward later, and the C element net release rate of leaves litter was fluctuated increased. Description, N treatments for the release of C element of camphor branches litter has a certain extent, while the leaves litter, showed a role in promoting slightly. With the nitrogen fertilization, nitrogen element in the state of concentration during the experiment. In two months, the N element net release rate of branches and leaves were increased （solid hysteresis） significantly. In four months, N solid lag decreases sharply. N solid stagnation was fluctuated downward later, but the decline was not obvious. Throughout the year, simulated nitrogen deposition on N net release rate of branches litter has a certain extent, but N treatments did not have a significant effect on N content of leaves litter. The K element net release rate of branches was the same as leaf litter’s, were shown to rise, then decrease. In two months, with the nitrogen fertilization （CK, LN, MN, HN）, there was a certain degree of solid hysteresis phenomenon on Ca element. In two to ten months, Ca net release rate was fluctuated to rise, was maximum （positive） in10months. Mg element in branches litter was similar to leaves litter’s, the performance was enrichment, then release. Mg net release rate of branches and leaves had a certain degree of solid hysteresis in two months. In10months, Mg element was in a released state and up to a maximum, Mg element content increased, and the Mg element net release rate was positive in12months. |
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