| Litter decomposition is an important way for nutrients cycling, but the litter decomposes slowly for the characteristics of plantation of fast-growing, short rotation and long-term single planting, which leads to soil productivity decline, especially for the coniferous tree. It is very important to learn the decomposition process and mechanism of litter for improving soil fertility and forest land quality.In this paper, the plantation of Larix kaempferi in temperate zone and north subtropical subalpine area were taken as the research object, and the micoorganism community were measured by combining qPCR, T-RFLP and DGGE in the litter of different development stands, different density stands and different composition. At the same time, the decomposition characteristics, nutrient characteristics and enzyme activities characteristics were measured. The correlation was analysed by Canonical correspondence analysis(CCA) and correlation analysis between microbial community and environmental factors to explore mechanism of microorganism in the process. The main conclusions from the study were as follows:(1) There was potential trend of soil productivity decline in Larix kaempferi with the development of the stands. The nutrient content, enzyme activity and microorganism quantity of topsoil(0-5cm) and litter firstly decreased, and then increased with the development of the stands, and they were all lowest in pre-mature stand, but the reserves of litter was highest in pre-mature stand. The reserves of litter was highest in semi-decomposed layer from young stand to pre-mature stand, while in decomposed layer in mature stand. The quantity of fungi and enzyme activities(except laccase) were in the following order: un-decomposed layer>semi-decomposed layer>decomposed layer, while the quantity of bacteria was in the following order: semi-decomposed layer>un-decomposed layer>decomposed layer. The succession characteristic of fungi community was more obvious than bacteria community among the different layers.(2) The decomposition rate of different composition litter were all faster in the early stage than later stage of decomposition and in growing season than non-growing season, but the decomposition rate was different. The content organic carbon, the ratio of C/N and C/P and residual rate of nutrients were all in the following order: broad leaf litter<mixing litter of needle and broad leaf<mixing litter of needle and shrub <needle litter, while the content of other nutrient element and decopositionl rate of litter were all in the following order: broad leaf litter >mixing litter of needle and broad leaf >mixing litter of needle and shrub >needle litter. The decomposition rate was faster and residual rate of nutrients were lower in lower density stand in temperate zone, but in higher density stand in north subtropical subalpine zone. The decomposition rate was faster in north subtropical subalpine zone than temperate zone. The variation trend of nutrient content and nutrient residual rate were similar in the same climatic zone, but were different in different climate zones.(3) The variation trend of different enzyme activities were basically the same in different climate zones, different density stand and different composition litter. The activities of amylase, invertase, acid phosphatase and alkaline phosphatase all appeared downtrend with the decomposition of litter. The activities of endocellulase and β-glucosidase appeared fluctuation trend with the decomposition of litter. The activities of laccase and polyphenoloxidase appeared uptrend with the decomposition of litter. The enzyme activities were highest in broad leaf litter and the mixing litter of broad leaf and needle leaf, then the mixing litter of needle leaf and shrub, and lowest in the needle litter. In the whole, the enzyme activities were higher in north subtropical subalpine zone than temperate zone,and the time of enzyme activities returning to high level was in April in north subtropical subalpine area and was until May in temperate zone.(4) The dominant bacteria and fungi were different in the decomposition of litter in different climate zones, different density stand and different composition litter. The quantity of bacteria and fungi were higher in the litter of lower ratio of C/N and in the lower density stand in temperate zone. The dominant bacteria were the basically the same that existed all the time in the process of decomposition, and dominant fungi appeared the similar regular. Most of the bacreria and fungi and their relative content was different in different composition litter in temperate zone. The quantity of bacteria was higher in the litter of lower C/N, but the quantity of fungi was higher in the litter of higher C/N, and they were all higher in the higher density stand in the north subtropical subalpine zone. The dominant bacteria and fungi were the basically different that existed all the time in the process of decomposition of different composition litter. The quantity of bacteria were higher in temperate zone, and the quantity of fungi were higher in the north subtropical subalpine zone. The species of dominant bacteria were basically the same, species of dominant fungi were different in different climate zones. The relative content of dominant fungi that existed all the time was general lower, and that appeared in a particular period was general higher. The density of stand had little effects on the species of dominant bacteria and fungi, but the time of most of microorganism colonizing and becoming dominant microorganism was different in different density stand. Most of bacteria beonged to Proteobacteria, Bacteroidetes and Actinobacteria, and more than 90% fungi belonged to Leotiomycetes and a few belonged to Agaricomycetes.(5) The relationship of quality of litter, decomposition rate, enzyme activity and quantity of microorganism were complex. The total decomposition rate was negative correlation with organic carbon, the ratio of C/N and C/P and positive correlation with other nutrient elements. The ratio of C/P and content of exchangeable Ca2+, exchangeable Mg2+ all had important effects on fungi community and bacteria community in temperate zone and north subtropical subalpine zone. pH had smaller effects on microbial community in different composition litter, but had greater effects on microbial community in different layer litter.The initial quality of litter had greater effects on decomposition rate and microorganism quantity in temperate zone than in north subtropical subalpine area and the correlation between microbial community and environment factors had obvious difference between the litter of lower C/N and the litter of higher C/N in temperate zone, which showed the quality of litter had more effects on decomposition in temperate zone. The correlation between microbial community and environment factors was higher in the early stage of decomposition than later stage. The fungi were more sensitive than bacteria to the change of enviromental, but the bacteria had higher correlation with initial quality than fungi. The dominant microbial that existed all the time was little effected by environment factors. The amylase, endocellulase, chitinase, β-glucosidase, laccase and polyphenoloxidase had obvious correlation with decomposition rate in temperate zone. But amylase, invertase, endocellulase, chitinase, and β-glucosidase had obvious correlation with decomposition rate in north subtropical subalpine zone. The cellulase and xylanase were mostly secreted by the fungi, and amylase and invertase were mostly secreted by the bacteria. Enzyme was not secreted by single-minded microorganisms, and was secreted by the synergistic effect fungi and bacteria. |
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