The Properties Of Soil Microorganism Communities In Alpine Timberline, Western Sichuan

Being highly sensitive to the influence of mans activities and the global climate change,timberline indicates the behavior of the regional climate and environmental changes.The research on timberline has become one of the major concerns in the aspect of global climate change.What's more,soil microorganisms play many important roles in soil ecological processes,affecting the ecosystem productivity for they are concerned with the nutrient cycling and energy flow in the ecosystem. Therefore researches of microorganisms in timberline soil are extraordinary significance to study the ecosystem process of timberline system.But so far,no reports about the soil microbe of timberline system in westen Sichuan have been published.The soil of alpine timberline in Wanglang Nature Reserve was selected to study the distribution of soil microorganisms in this paper.The quantity of soil microorganisms and microbial functional groups were analyzed by plate counting method.The effect of soil microorganisms were discussed in the soil form and the pattern of vegetation distribution.The main research purpose was to provide a basic microorganism data for other research of timberline in western Sichuan alpine.The results are as follows:In the timberline soil,the amount of bacteria was the largest,which was followed by that of fungi,and then that of actinomycetes.Bacteria covered 76.16%～80.73%of the total amount of microorganisms,fungi about 17.54%～19.86%, actinomycetes only 1.73%～3.97%.It was evident that the soil bacteria takes advantage in the decomposition of organic materials and rises the main function in transforming of substance and forming of fertility in soil,but the actinomycetes was little and its function was very tiny in timberline. Vertically quantitative distribution of various microorganism groups showed that, the deeper the soil,the less the microorganism.The numbers of soil microbes of the same group varied greatly in soil with a depth of 0～60cm,among which bacteria was 1.34×105～1.37×107cell·g-1,fungi 2.47×105～2.97×106 cell.g-1,actinomyces 0.24×105～2.92×105 cell·g-1 in July.The result showed that microbes mainly concentrated in the 0-20cm soil layer,which was very important active in the soil microorganisms.The amount of bacteria,fungi and actinomyces varied obviously with seasons. Compare of the three seasons,there were more microorganism in July,and the least microorganism in May.There is close relation in the variety of the soil microorganisms with the season and the weather factor in timberline.The correlation analysis between the quantity of soil microoganisms and physics and chemistry factor of the soil showed that there is a positive relationship between total N and actinomycetes(P＜0.05),a positive relationship between available-N and bacteria(P＜0.05),and an extremely one between available-N and fungi.The content of soil organic matter had significant correlation with three kinds of microbes(P＜0.05).However,the relationship between three microbes and soil moisture,soil pH and available-P was not significant.The quantity of bacteria,fungi and actinomyces were were different in three forest lands.There was the most in imberline,the next was alpine meadow stand, and the fewest was in fir forest.Among the different soil microbial functional groups in the timberline system, the order of the quantity of them was ammonifying bacteria＞organic phosphorus-decomposing bacteria＞inorganic phosphorus-decomposing bacteria＞silicate-dissolving bacteria＞aerobic nitrogen fixing bacteria＞nitroso bacteria＞aerobe cellulose-decomposing bacteria＞anaerobic cellulose-decomposing bacteria. The dominant population of bacteria functional groups was the genus of ammonifying bacteria,organic phosphorus-decomposing bacteria,inorganic phosphorus-decomposing bacteria,silicate-dissolving bacteria,and aerobic nitrogen fixing bacteria(over 97%),the decomposition and biomineralization of the soil N and P were stronger in timberline.The quantity of nitrosobacteria was too low,nitrification was very weak.Aerobic cellulose-decomposing bacteria and anaerobic cellulose-decomposing bacteria were too little to be checked by the cell enumeration methods(MPN).The low temperature in timberline does not benefited in their growing and breeding and resolving and exercising their function.The numbers of the microbial functional groups in soil varied greatly with a depth of 0-60cm,the deeper the soil,the less the microorganism.The result showed that microbial functional groups mainly concentrated in the 0-20cm soil layer,and the 0-20cm layer of soils was very important active in the soil microorganisms.The amount of ammonifying bacteria,nitrogen fixing bacteria, silicate-dissolving bacteria,organic phosphorus-decomposing bacteria, nitrosobacteria and inorganic phosphorus-decomposing bacteria obviously varied with seasons.Although the amounts of aerobe celllulolytie microoganisms and oligotrophic cellulolytic microorganisms were too low,they were the most in July.The correlation analysis between the quantity of microbial functional groups and physics and chemistry factor of the soil showed that total N is correlated significantly with aerobic nitrogen fixing bacteria and organic phosphorus-decomposing bacteria. Soil available-N was correlated significantly with silicate-dissolving bacteria,with ammonifying bacteria and inorganic phosphorus-decomposing bacteria.The content of soil organic matter had significant correlation with every soil microorganisms(P＜0.05),and The correlation between the soil organic matter content and Silicate-dissolving bacteria had reached extremely significant level(P＜0.01). However,the relationship between every microorganism and soil moisture,soil pH and available-P was not significant.Comparing to the timberline,the fir forest and the alpine meadow,the quantity of microbial functional groups was different.Quantities of ammonifying bacteria, aerobic nitrogen fixing bacteria,organic phosphorus-decomposing bacteria,and silicate-dissolving bacteria were the most in timberline stand,the next is alpine meadow stand,and those in fir forest stand were the fewest.Quantities of inorganic phosphorus-decomposing bacteria,nitroso bacteria,aerobe celllulolytie bacteria,and oligotrophic cellulolytic bacteria were the highest in timberline stand,and those in fir forest land were lower than those in alpine meadow stands.All the data showed that the total species numbers of soil microorganisms in timberline soil were the most.