| The study on decomposing of litters and soil respiration traits and the influences of modeling up nitrogen deposition on the natural ever-green forests eco-system were conducted as reference and theory to the management and supervision of the natural sub-tropical forests eco-system. The deep study on mechanism of the forest eco-system's response to nitrogen decomposing was conducted as the reference of the influence of nitrogen decomposing, and protection of plantation in the similar areas and the basic data for the degraded ever-green forest's regeneration and renewal.Experiment 1: The study was conducted in natural evergreen broad-leaf forest(EBF) in southwest of Sichuan Province. Nitrogen addition experiments were initiated within the forest in 2005. Four nitrogen addition treatments(in three replicates) were established in the forest: control(0 kg N·hm-2·a-1, CK), low nitrogen (50 kg N·hm-2·a-1, LN), medium nitrogen(100 kg N·hm-2·a-1, MN) and high nitrogen(150 kg N·hm-2·a-1, HN). All plots (2m×2m) and treatments were laid out randomly. Ammonium nitrate (NH4NO3) solution was sprayed monthly onto the floor of these plots as 12 equal applications over the whole year and beginning in July 2005.Litter decomposition was determined by using closed, mesh litter bags in the plots. A total of 288 bags of EBF litter were prepared from mesh(0.5 mm in the bottom and 2 mm in the top) polyvinyl screen of approximately 25 cm×25 cm in dimension. Each bag was filled with about 0.02 kg, air-dried mass, of litter. In July 2005, these litter bags were evenly distributed among 3 subplots selected randomly. Four litter bags were collected from each plot at about 92, 183, 214, 244, 274 and 365 days after the start of the experiment.Experiment 2: This study was conducted in native evergreen broadleaf forests aiming at measuring soil respiration and the effects of nitrogen deposition on soil CO2 emission. Nitrogen addition experiments were carried out within the forest selected in 2005. Four nitrogen addition treatments(in three replicates) were established in mature forest: control(0 kg N·hm-2·a-1, CK), low nitrogen (50 kg N·hm-2·a-1, LN), medium nitrogen(100 kg N·hm-2·a-1, MN) and high nitrogen (150 kg N·hm-2·a-1, HN). Twelve plots (2m×2m) were set up. All plots and treatments were laid out randomly. Ammonium nitrate(NH4NO3) solution was sprayed monthly by hand onto the floor of these plots as 12 equal applications over the whole year and beginning in July 2005.Soil respiration was measured three to five times at mid month from October 2005 to July 2006 through alkali sorption technique. And temperature of top soil and soil at 10 cm depth and water content at 0～10 cm, 10～20 cm were menstruated at each measurement occasion.The results showed that:(1) The results showed that 95％of litter mass loss under the nitrogen treatments would take 4.72 to 6.33 years to decompose at a rate of the highest coefficient of CK(0.6352 kg·kg-1·a-1) and the lowest coefficient of HN (0.4735 kg·kg-1·a-1). After 365days, litter decomposition rate with HN, MN and LN treatments was 39.98％, 44.21％and 42.51％respectively, all of which were lower than that of CK(50.08％), but significant difference was only tested between HN and CK (P=0.05). Moreover, the remained C proportion in HN (59.18％), MN (51.95％) and LN (55.28％) was higher than that of CK(50.05％) whereas the remained N proportion was 48.14％in HN, 50.03％in MN and 47.88％in LN, respectively, all of which were also significantly higher than that in CK(40.78％, P=0.05). The remained P proportion in HN, MN and LN was 60.80％, 57.05％and 65.02％, respectively, all of which were higher than that of CK(55.27％), but significant difference was only found between LN and CK (P=0.05). However, the remained K proportion was 39.66% in HN, 47.91% in MN and 36.18% in LN, all of which were significantly higher than that in CK (26.42%, P=0.05). Compared with the original C/N ratio (62.35), the litter C/N ratio was increased from 3.9% to 23.7%, but the changing trend was not obviously regular. Changes on N content in the decomposed litter featured a pattern of nutrient accumulation in the early stage and release in the late stage of decomposition, while C, P and K released directly. Subsequently, nitrogen-addition treatments could inhibit the release of nutrient elements and the decomposition of lignin and cellulose as well. Generally, effects of nitrogen deposition on litter decomposition in the evergreen broad-leaved forest in southwestern Sichuan suggested a change from positive to negative trend as time passed, and the negative effect could be strengthened with the increase of the deposited nitrogen concentration.(2) Soil respiration rate varied from 612.21±77.82 mg CO2·m-2·h-1 to 108.95±17.01 mg CO2·m-2·h-1 in the forest reach a minimum in February and maximum in July. The model Rs=aebTWc (Rs soil respiration rate, T soil temperature, W soil water content, and a, b, c the constants) indicated that both soil temperature and soil water content could explain 68.6%～73.9% of seasonal variation in soil respiration rates. Soil temperature and soil water content could explain 67.8%～73.8%, 1.2%～4.77% seasonal variation of them. Furthermore, soil temperature would become a mainly limiting factor for soil respiration in the experiment. The Q10 values were 2.12(soil surface) and 2.51(5 cm soil depth). (2) HN (309.43±17.24 mg CO2·m-2·h-1 and MN (303.82±11.50 mg CO2·m-2·h-1) at 0.05 levels were significantly stimulated soil respiration in the forest compared with the control plot (CK, 269.28±13.78 mg CO2·m-2·h-1) after 3 months, HN (272.42±13.25 mg CO2·m-2·h-1) was significantly increased compared with those in CK (234.51±12.77 mg CO2·m-2·h-1) after 4 months. However, there was no significant differences between nitrogen addition at any level of treatment and compared with CK on soil CO2 emission during February～July 2006. As a whole, nitrogen deposition stimulated soil respiration significantly at an early stage, no significant effect at the late stage.
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