| Atmospheric N deposition continues increasing results from intensified agricultural and industry. China has been the world’s third-largest N deposition area and the speed N deposition is still on the increase year by year. N deposition has affected on species composition of forest communities, and the changes of species composition leads to litter amount and composition change, which will change the number and construction of soil microorganisms and animals. The soil microorganisms have an important effected on forest ecology biochemical circulation, they participate in material circulation and energy flow in the forest ecological system, and play a very important role in maintaining the structure and function of ecosystem. Cryptomeria fortune, as one of the main afforestationtree species in subtropical region of China, has a high economic value. Therefore, from January 2012 to July 2013, 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 microorganisms to the simulated nitrogen deposition and the litter composition changes. A total of 12 treatments were set:CK(Comparison)、LN(Low N,5 g·m-2·a-1)、MN(Middle N,10 g·m-2·a-1)、 HN(High N,15 g·m-2·a-1), SL(Cunninghamia lanceolata litter mixed with Cryptomeria fortunei at a ratio of 1:1)、NL(Phoebe bournei litter mixed with Cryptomeria fortunei at a ratio of 1:1)、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 within 1.5a. N deposition significantly increased the number of soil bacteria (p<0.05), and the bigger the concentration, the more the number of bacteria.LN significantly increased the number of soilfungi(p<0.05),MN and HN significantly refrained the number of soil fungi(p<0.05), and the bigger the concentration,the less the number of fungi. LN and MN increased the number of soil actinomycetes,MN had the strongest effect, HN refrained the number of actinomycetes. Different soil microbes showed different seasonal variation characteristics under different nitrogen deposition levels.(2) During the trial within 1.5a. Different litter composition significantly increased the number of soil bacteria (p<0.05), and the size of the order was SL< NL. Different litter composition significantly increased the number of soil fungi (p<0.05), and the size of the order was NL< SL. Different litter composition increased the number of soil actinomycetes(p<0.05), and the size of the order was NL< SL. Different soil microbes showed different seasonal variation characteristics under different litter composition.(3) During the trial within 1.5a. N deposition and adding litter had significant interaction effects on the number of soil microorganism. On the 270th days of the trial, N15SL and N15NL significantly refrained the number of bacteria(p<0.05), other deals significantly increased the number. On the 270th days of the trial, N5NL、NIOSL、N15SL and N15NL refrained the number of fungi, other deals increasedthe number. All deals increasedthe number of actinomycetes. Different soil microbes showed different seasonal variation characteristics under two-factor interaction.(4) During the trial within 1.5a. LN significantly improved MBC(p<0.05), MN and HN significantly improved MBC in preliminary trials(la) (p<0.05), and decreased MBC in the end of the trial period(p<0.05). LN and MN significantly improved MBN(p<0.05), HN significantly improved MBN in preliminary trials(p<0.05), and decreased MBN in the end of the trial period(540d). MB showed different seasonal variation characteristics under different nitrogen deposition levels.(5) During the trial within 1.5a. Different litter composition significantly improved MBC (p<0.05), and the size of the order was SL< NL. Different litter composition significantly improved MBN (p<0.05), and the size of the order was SL< NL.MB showed different seasonal variation characteristics under different litter composition.(6) During the trial within 1.5a. N deposition and adding litter had significant interaction effects on the MB. N5SL、N5NL、N10SL、N15SL and N15NL on the 180th days of the trial, N5SL、N5NL and N10NL on the 270th days of the trial, N5SL and N10SL on the 360th days of the trial, N5SL and N5NLon the 450th days of the trial and N5SL and N5NL on the 540th days of the trial decreased the MBC. N5SL and N5NL on the 180th days of the trial,N5SL、N10NL and N15NL on the 270th days of the trial, N5SL and N15NL on the 450th days of the trial decreased the MBN. Other deals improved MB. MB showed different seasonal variation characteristics under two-factor interaction.(7) During the trial within 1.5a. N deposition significantly improved SOC, SOC was the highest under MN. SOC showed different seasonal variation characteristics under different nitrogen deposition levels.(8) During the trial within 1.5a. Different litter composition significantly improved SOC (p<0.05), and the size of the order was SL< NL. SOC showed different seasonal variation characteristics under different litter composition.(9) During the trial within 1.5a. N deposition and adding litter had significant interaction effects on SOC. N10NL decreased SOC. N10SL decreased SOC except 450d. N15NL became to decrease SOC after 450d. Other deals improved SOC. SOC showed different seasonal variation characteristics under two-factor interaction.Comprehensive analysis showed that N deposition and adding litter significantly change the soil microbial populations and biomass in Cryptomeria forest, and the populations and biomasscan be changed obviously with the change in the outside world. However, adding litter can alleviate the pressure come from nitrogen deposition and increase soil carbon stock. As an important part of forest ecosystem, the changing of the soil microbial populations and biomasscansensitively react the change of environment. In recent years, soil microbes become an important measure of global climate change because of its sensibility. Which means that build mixed forest could ease the negative impacts from nitrogen deposition and other of global climate change on forest ecosystem in a certain extent, and maintain and improve the forest soil quality. |
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