| In recent years,due to the burning of fossil fuels,the rapid development of transportation industry,and the rapid growth of industry and human activities,the concentration of nitrogen and sulfur in the atmosphere has increased.Excessive nitrogen and sulfur deposition has caused many ecological problems,and has aroused widespread concern of scholars at home and abroad.Forest soil nutrients and enzyme activities play an important role in carbon and nitrogen cycling in forest ecosystems.Based on this condition,the research take the natural evergreen broad-leaved forest located in rainy area of West China as the research object,from April 2013 to April 2015,we positioning simulated the nitrogen and sulfur deposition,studied the soil of evergreen broad-leaved forest(0-20cm layer)on its content of main nutrient,and also the response of enzyme activities to nitrogen,sulfur and their compound deposition.The purpose of this study was to provide reference data for assessing the effects of atmospheric nitrogen and sulfur deposition on forest soil ecological processes in the future.The experiments were set up in 9 treatments:control(CK,0 g-N·m-2·a-1,0 g·S·m-2·a-1),low nitrogen(LN,5 g·N·m-2·a-1)and high nitrogen(HN,15 g·N·m-2·a-1),low sulfur(LS,20 g·S·m-2·a-1)and high sulfur(HS,40 g·S·m-2·a-1),low nitrogen and low sulfur(LNLS,5 g·N·m-2·a-1,20 g ·S·m-2·a-1),low nitrogen and high sulfur(LNHS,5 g·N·m-2·a-1,40 g·S·m-2·a-1),high nitrogen and low sulfur(HNLS,15 g·N·m-2·a-1,20 g·S·m-2·a-1)and high sulfur and high nitrogen(HNHS,15 g ·N·m-2·a-1,40 g·S·m-2·a-1).The main results are as follows:(1)Nitrogen deposition had reduced the soil organic matter content in the natural evergreen broad-leaved forest in rainy area of West China.LN and HN treatments decreased by 7.85%and 12.56%.The content of soil organic matter in the evergreen broad-leaved forest with high sulfur deposition was decreased by 7.27%,but no significant effect was found in the low sulfur deposition.The interaction of nitrogen and sulfur deposition was obvious.the LNLS,LNHS,HNLS and HNHS treatments has decreased the soil organic matter content of evergreen broad-leaved forest,which decreased by 11.97%,9.13%,13.43%and 15.80%,respectively.There was a Synergistic effect between the treatments of low sulfur and low nitrogen,low sulfur and high nitrogen,high nitrogen and low sulfur,high nitrogen and high sulfur compound deposition.(2)High nitrogen deposition had increased the soil total nitrogen content in natural evergreen broad-leaved forest in rainy area of West China,with an increase of 10.43%.No significant effect was found in Low nitrogen deposition.The content of total nitrogen under the low sulfur decomposition decreased by 2.32%,while the high sulfur deposition had no significant effect.The interaction of nitrogen and sulfur deposition was obvious.LSLN,HNLS and HNHS treatment increased the total nitrogen content of evergreen broad-leaved forest soil,increased by 6.31%,11.84%and 12.55%,respectively.There was a Synergistic effect between low sulfcur and low nitrogen,high nitrogen and low sulfur,high nitrogen and high sulfur compound deposition.(3)Nitrogen,sulfur and its compound deposition had no significant effect on total phosphorus and total potassium content of natural evergreen broad-leaved forest in the rainy area of West china.(4)Nitrogen deposition has reduced the C/N of forest soil.LN and HN treatment were decreased by 11.17%and 20.05%;sulfur deposition has no obvious effect on soil C/N;nitrogen and sulfur compound deposition has obvious interaction on soil C/N.There was a synergistic effect between the treatments of low nitrogen and high sulfur,low sulfur and low nitrogen,high nitrogen and high sulfur,high nitrogen and high sulfur deposition.Nitrogen deposition decreased soil C/P.LN and HN were decreased by 6.87%and 10.13%,respectively;sulfur deposition has no obvious effect on soil C/P;nitrogen and sulfur compound deposition has obvious interaction on soil C/P,synergistic effect was found between the treatments of low sulfur and low nitrogen,high nitrogen and low sulfur,high nitrogen and high sulfur deposition.Nitrogen deposition increased soil N/P,LN and HN were increased by 4.46%and 13.33%;soil with treatment of high sulfur increased by 5.58%,low sulfur deposition has no obvious effect on soil N/P;nitrogen and sulfur compound deposition has obvious interaction on soil N/P,synergistic effect was found between the treatments of low nitrogen and low sulfur,low nitrogen and high sulfur,high nitrogen and the high sulfur.antagonistic effect was found between the treatments of high nitrogen and low sulfur deposition.(5)The 7 kinds of soil enzyme activities in the natural evergreen broad-leaved forest in rainy area of West China had obvious seasonal dynamics.Among them,the cellulose activity,urease activity and polyphenol oxidase activity are higher in autumn,Sucrase activity,Acid phosphatase activity were higher in spring.Catalase activity and peroxidase activity were higher in winter.The seasonal dynamics of soil enzyme activities were not affected by simulated N,P and its compound deposition.(6)Nitrogen deposition had no significant effect on the activities of invertase and catalase in the natural evergreen broad-leaved forest of the rain area,and promoted the activity of urease,acid phosphatase,inhibited the activity of peroxidase;High nitrogen deposition inhibited the activity of cellulase and polyphenol oxidase.Sulfur deposition had no effect on the activity of cellulase and catalase,and promoted the activity of acid phosphatase;The deposition of low sulfur promoted the activity of invertase.The activity of invertase,urease,polyphenol oxidase and peroxidase was inhibited by high sulfur deposition.Deposition of nitrogen and sulfur had no significant effect on cellulase and catalase activity,but had obvious interaction on activity of invertase,urease,acid phosphatase,polyphenol oxidase and peroxidase.For sucrose enzyme,high nitrogen and high sulfur compound deposition had synergistic effect,and high nitrogen and low sulfur compound deposition had antagonistic action.For urease,nitrogen deposition was dominant in nitrogen and sulfur deposition.For acid phosphatase,there was a synergy between the treatments of high nitrogen and low sulfur,low nitrogen and low sulfur compound deposition.For polyphenol oxidase,there was a synergistic effect between high nitrogen and high sulfur deposition.For peroxidase,there was a synergistic effect between treatments of high nitrogen and low sulfur,high nitrogen and high sulfur deposition... |
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