Effects Of Simulated Nitrogen Deposition And Litter Composition On Soil Enzyme Activities In A Cryptomeria Fortune Plantation

China is the world’s third-largest nitrogen deposition area and atmospheric nitrogen deposition has had a serious impact on China’s forest ecosystems. The increase of atmospheric nitrogen deposition has affected the plant composition of the forest communities, while changes in the composition of plants cause changes of the amount and composition of litter, thereby affecting the biochemical processes of the soil. Soil enzymes play an important role in the process of forest material circulation and energy flow and have certain indication to the biochemical processes of soil. Cryptomeria fortune, as one of the main afforestation tree species in subtropical region of China, has a high economic value. Therefore, from January2012to January2013, by simulating the nitrogen deposition and changing the litter composition in the study area of Cryptomeria fortunei plantation in the heart of the Rainy Area of West China, this thesis studied the responses of soil enzyme activity to the simulated nitrogen deposition and the litter composition changes. A total of12treatments were set:CK(Comparison)、LN(Low N,5g·m-2·a-1)、MN(Middle N,10g·m-2·a-1)、HN(High N,15g·m-2·a-1)、SL(Cunninghamia lanceolata litter mixed with Cryptomeria fortunei at a ratio of1:1)、HL(Phoebe bournei litter mixed with Cryptomeria fortunei at a ratio of1:1)、LNSL(Low N+Cunninghamia lanceolata litter mixed with Cryptomeria fortunei)、MNSL(Middle-N+Cunninghamia lanceolata litter mixed with Cryptomeria fortunei)、 HNSL(High N+Cunninghamia lanceolata litter mixed with Cryptomeria fortunei)、LNNL(Low N+Phoebe bournei litter mixed with Cryptomeria fortunei)、MNNL(Middle N+Phoebe bournei litter mixed with Cryptomeria fortunei) and HNNL(High N+Phoebe bournei litter mixed with Cryptomeria fortunei).The main results were as follows:(1) During the trial period, N deposition significantly increased the soil cellulase activity in a Cryptomeria forunei plantation (p<0.05). Among the changes in litter composition, treatment NL significantly increased the soil cellulase activity (p<0.05), and treatment SL had no significant effect, while the soil cellulase activity of treatment NL was significantly higher than treatment SL (p<0.05). As to N deposition well changes in litter composition, the soil cellulase activity in all treatments were all significantly increased (p<0.05), the soil cellulase activity in different treatments of different periods was stimulated to varies degrees and showd no obvious rule.(2) During the trial period, N deposition significantly increased the soil sucrase activity in a Cryptomeria forunei plantation(p<0.05). Among the changes in litter composition, treatment NL significantly increased the soil sucrase activity (p<0.05), while treatment SL significantly increased the soil sucrase activity in the later (p<0.05), and the soil sucrase activity of treatment NL was significantly higher than treatment SL(p<0.05). As to N deposition well changes in litter composition, the treatments were all significantly increased the soil sucrase activity(p<0.05), different treatments in different periods stimulated the activity of soil sucrase to varying degrees, and treatment LNSL had the highest soil sucrase activity overall.(3) During the trial period, N deposition significantly increased the soil acdic phosphatase activity in a Cryptomeria forunei plantation (p<0.05), the soil acdic phosphatase activity of treatment NL had a downward trend. Changes in litter composition significantly increased the soil acdic phosphatase activity (p<0.05), the soil acdic phosphatase activity of treatment NL was significantly higher than treatment SL (p<0.05). As to N deposition well changes in litter composition, the soil acdic phosphatase activity in treatments of MNSL、HNSL、LNNL and HNNL were significantly increased (p<0.05), while the activity in treatments of LNSL and MNNL had no significant change overall.(4) During the trial period, N deposition significantly increased the soil urease activity in a Cryptomeria forunei plantation (p<0.05), treatment HN had the highest soil urease activity. Changes in litter composition significantly increased the soil urease activity (p<0.05), the soil urease activity of treatment SL was significantly higher than treatment NL (p<0.05). As to N deposition well changes in litter composition, the treatments were all significantly increased the soil urease activity (p<0.05).(5) During the trial period, N deposition showd some inhibitory effect on the soil polyphenol oxidase activity in a Cryptomeria forunei plantation, but not significantly. Changes in litter composition had no significant effect on the soil polyphenol oxidase activity. As to N deposition well changes in litter composition, treatment MNSL significantly inhibited the soil polyphenol oxidase activity in general (p<0.05), while treatment LNNL significantly inhibited the soil polyphenol oxidase activity in prophase (p<0.05), but had no significant effect in the later, and treatment HNNL had no significant effect overall. Changes of the soil polyphenol oxidase activity in the other treaments were complex and showd no obvious rule.(6) During the trial period, N deposition showd some inhibitory effect on the soil hydrogen peroxidase activity in a Cryptomeria forunei plantation, and treatment HN had a significant effect (p<0.05). Among the changes in litter composition, the soil hydrogen peroxidase activity of the treatments SL and NL increased to some extent, but not significantly. As to N deposition well changes in litter composition, treatments HNSL and LNNL significantly inhibited the soil hydrogen peroxidase activity overall (p<0.05), whlie treatment LNSL had no significant effect in prophase but significantly inhibited the soil polyphenol oxidase activity in the later (p<0.05), and treatment MNNL in general showd some inhibitory effect on the soil hydrogen peroxidase activity and inhibited significantly in the later. Changes of the soil hydrogen peroxidase activity in the other treaments were complex and showd no obvious rule.