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Effects Of Simulated Nitrogen Deposition On Microbial Biomass And Enzyme Activity During Litter Decomposition

Posted on:2020-01-20Degree:MasterType:Thesis
Country:ChinaCandidate:S P HuangFull Text:PDF
GTID:2480305909980389Subject:Forest management
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In recent years,with the rapid development of China's economy,atmospheric nitrogen deposition is also increasing rapidly.Up to now,China's annual nitrogen emissions have exceeded 15 million tons,becoming the largest nitrogen deposition area in Asia.Excessive nitrogen input will affect the decomposition process and rate of forest litter,and then affect the material cycle and energy flow of ecosystem.As decomposers and drivers of litter,microbial communities and enzymes are very sensitive to nitrogen deposition.However,at present,the research on microbial community and enzyme activity is mainly concentrated in the soil layer,and there are few reports on microbial community and enzyme activity in the process of litter decomposition.Rainy Area of Western China is a long and rainy area with high nitrogen load in the west of Sichuan Basin,and wet nitrogen deposition is extremely significant.Based on this,this study took the natural evergreen broad-leaved forest in Rainy Area of Western China as the research object.From March 2016 to March 2017,NH4NO3was used to simulate nitrogen deposition every 15 days.The nitrogen application levels were compared(CK,0 kg N hm-2.a-1),low nitrogen(LN,50 kg N hm-2.a-1),medium nitrogen(MN,150 kg N hm-2.a-1)and high nitrogen(HN,300 kg N hm-2.a-1).The aim of this study is to provide basic data for revealing the mechanism of simulated nitrogen deposition on litter decomposition,and to provide reference for sustainable management and development of natural evergreen broad-leaved forest in Rainy Area of Western China.The results show that:(1)Compared with CK treatment,the litter mass residue rates of LN,MN and HN treatment increased significantly by 2.11%,5.76%and 10.29%after 1 year of simulated nitrogen deposition experiment,and the decomposition time of 95%litter increased significantly by 0.43a,1.04a and 2.06a,respectively.This indicates that simulated nitrogen deposition inhibits litter decomposition,and the higher the simulated nitrogen deposition intensity,the stronger the inhibition.(2)Compared with CK treatment,LN treatment had no significant effect on the total microbial biomass during litter decomposition,while MN and HN treatment significantly reduced the total microbial biomass by 20.02%and 37.68%,respectively.This indicated that low nitrogen treatment had no significant effect on the total microbial biomass during litter decomposition,while medium and high nitrogen treatment significantly inhibited the total microbial biomass,and the higher the simulated nitrogen deposition intensity,the stronger the inhibition.(3)Compared with CK treatment,LN treatment had no significant effect on the number of bacteria and fungi during litter decomposition;MN treatment significantly reduced the number of bacteria and fungi by 19.27%and 30.40%,and HN treatment significantly reduced the number of bacteria and fungi by 42.37%and 36.91%.This indicated that low nitrogen treatment had no significant effect on the number of bacteria and fungi during litter decomposition,while medium and high nitrogen treatment inhibited the number of bacteria and fungi,and the higher the simulated nitrogen deposition intensity,the stronger the inhibition.(4)Compared with CK treatment,the number of actinomycetes in LN treatment increased by 42.76%,while that in MN and HN treatment decreased by 21.28%and22.76%.This indicated that low nitrogen treatment promoted the number of actinomycetes during litter decomposition,while medium and high nitrogen treatment inhibited the number of actinomycetes.(5)Compared with CK treatment,LN treatment significantly promoted the activities of sucrase,urease,peroxidase,acid phosphatase and catalase during litter decomposition,and significantly inhibited the activities of polyphenol oxidase and cellulase;MN treatment significantly promoted the activities of urease and peroxidase during litter decomposition,and significantly inhibited the activities of polyphenol oxidase.The activities of urease,peroxidase,polyphenol oxidase,catalase and cellulase during litter decomposition were studied.This indicated that there were significant differences in the effects of simulated nitrogen deposition on enzyme activities during litter decomposition.(6)After a one-year simulated nitrogen deposition experiment,the number of bacteria alone could explain 84.6%of the variation of K value of litter decomposition coefficient,fungi alone could explain 57.3%of the variation of K value,while actinomycetes could not effectively explain the variation of K value;polyphenol oxidase activity alone could explain 74.2%of the variation of K value during litter decomposition;catalase activity alone could explain 74.2%of the variation of K value.The variation of K value was explained by 36.8%alone,but the activities of sucrase,urease,peroxidase,acid phosphatase and cellulase during litter decomposition could not explain the variation of K value effectively.The number of bacteria and the activity of polyphenol oxidase during litter decomposition explained 91.0%of the variation of K value together.This suggests that simulated nitrogen deposition may be mainly through inhibiting the number of bacteria and polyphenol oxidase activity in the process of litter decomposition to inhibit litter decomposition.
Keywords/Search Tags:simulated nitrogen deposition, Natural evergreen broad-leaved Forest, Litter decomposition, microbes, enzyme activities, Rainy Area of Western China
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