Microbial Community Distribution In Different Water-stable Aggregate

Soil aggregates are the basic units of soil structure, and the niche of microbes. Microorganisms play an important role in soil aggregate formation. The amount and quality of soil aggregate have directly affect on keeping water and nutrient ,in this study ,five soils with different managements were collected from JinYun mountain area and separated by wet-sieving technique into 4.76-2.0,2.0-1.0,1.0-0.25,0.25-0.053 and <0.053mm aggregate fractions and the soil microbial biomass, community structure and function were determined.The result show that the overall pattern indicates higher accumulation of C,N and P in the WSA of the grassland soils over the forest soils. The <0.053 mm aggregate fractions were preferentially enriched with Ca²⁺,Mg²⁺ ,K⁺, and Na⁺, since smaller aggregates are preferentially removed by erosion. The amounts of fungi were the most within the soil aggregate of 0.25～1.0mm under ridge no-tillage, and the diversity of fungi shows similar trends. While the amounts of fungi were the most within the soil aggregate less than 0.053mm under paddy-upland rotation system, ridge no-tillage seems provide a more favorite micro-environment for microorganisms. the soil nutrients under ridge no-tillage (Total N and P). organic matter contents are more than those under paddy-upland rotation system. Under ridge and no-tillage, the characteristics of microbial community in surface soils distribute like this: bacteria> fungi > actinomycete. Bacteria and fungi exist most in the soil aggregate size<0.053mm, while actinomycete exists most in the soil aggregate size<0.200mm. Ridge no-tillage in paddy fields is good for improving the soil ecosystem and increasing the soil fertility. The content of microbial biomass N of the soil and aggregate were all highest in ridge no-tillage, Significant correlation between soil microbial biomass N and total N, microbial biomass N and ammonium nitrogen were found and no significant correlation between soil microbial biomass N and nitrate nitrogen. Distribution of microbial biomass N in the 2.0-1.0mm fraction for the grass land higher than it was for the Chinese red pine, and in the other fraction it was the highest for the grass land.