Studies On Soil Microbial Community Structure Based On Phospholipid Fatty Acid (PLFA) Analysis

Soil microbes are the decomposers of ecosystem, play an important role in keepingecosystem balance. However, as there are large range of soil microbes and the habitatin which they live is very complicated, our knowledge about this versatile microbialcommunity is very limeted. Thus, the thesis is stringed along soil microbialcommunity structure to study the distribution of soil microbes and the relationshipbetween soil microbial diversity and ecosystem function, based on the phospholipidfatty acid(PLFA) analysis. The following main results were obtained:The methods about using PLFAs to identify pure soil bacteria strains, extractingand quantifying PLFAs from soils were built first time in China. Moreover, weoptimized the soil PLFAs extraction method, which is an important complementary tosoil PLFA extraction in the world and the first integrated, easy handling PLFAextracting methods in China.We collected 14 typical climate zonal soils from north to south of China andmeasured the soil microbial PLFAs. The results showed that soil microbes are just likeplants and animals, distributing regularly from north to south. The northern soilscontain more gram positive bacterial PLFAs, while the southern soils have more gramnegative and fungi PLFAs. Mean annual rainfall and soil pH are the two majorcontributors to the distribution of soil microbes in this study.Besides, Heilongjiang, Jiangsu and Guangxi soils were used to determine theresponses of soil microbes under incubation at different temperature and water content.The results showed that the response of soil microbes to different temperature wascorrelated with the climate history of the sampling site. The microbial biomass andcommunity structure of Heilongjiang soil(from the coldest temperature region)changed most when incubated at 35℃. Guangxi soil from the hottest region changedleast. Both soil microbial biomass and community structure did not change very muchwhen soils were incubated at 40-80% WHC for up to 56 days..Three very contrasting managements: permanent fallow, permanent arable andpermanent grassland, which have been applied from the same soil for at least 60 years,were used to determine the relationships of community structure and ecosystemfunction(mineralizing labile substrates(yeast extract) and more complex substrate (ryegrass)). The results showed that although the three soils have quite differentmicrobial biomass and community structures, the metabolism of the substrates and theefficiencies of microbial biosynthesis were quite similar. The ability of mineralizationwas mainly determined by the type of substrates. Soil microbial community structuresmeasured by PLFA analysis responded differently to different substrates, mainlydetermined by the history of substrates utilization.Arable and grassland soils collected from Highfield Ley-Arable experiment wereused to determine the response of soil microbes to chloroform fumigation. Thecommunity structure was indexed by DNA-DGGE method. Chloroform fumigationkilled most but not all microbes. However, the respiration rate did not decrease in thechloroform fumigated soils. Soil microbial community structures after chloroformfumigation were quite similar to that in the heat-resistant spore forming treated soils.Spores may be the predominant microbes left after chloroform fumigation.