Soil microbes play important roles in regulating bio- geo chemical process and functions of ecosystem. Knowledge about the microbial distribution patterns and mechanisms of its formation have important theoretical and practical significance. Existed research was concentrated in 0-20cm soil profile and few work concerned deeper zones, especially on big geographical scale.

Environment factors such as pH, physical texture, nutrients, moisture, and temperature of soil affect the distribution of soil microbes. However, the factors contributed to vertical microbe distribution along soil profile has not been determined in large geographical scale.

The research group of Microbial Resources and Ecology from Institute of Applied Ecology (IAE) of the Chinese Academy of Sciences in IAE have collected paddy soil samples from 0-100cm profile from Hailun, Heilongjiang Province, Changshu, Jiangsu Province and Yingtan, Jiangxi Province. Changes in biomass, diversity and community structure of soil microbe were investigated by phospholipid fatty acid (PLFA) method and illustrated the major related environmental factors. 

It was found that the total biomass and diversity of microbes significantly decreased with the depth on the profile, especially from surface to 40cm. Different group showed different patterns: the biomass of bacteria and fungus decreased in 0-40cm and gradually increased in 40-100cm. The biomass of actinomysetes showed reversed pattern. Along with the deepness on the profile, the proportion of Gram-positive bacteria increased and Gram-negative bacteria showed decrease.

Canonical correspondence analysis and Pearson's correlation analysis indicated that both the geographic locality (paddy soil type) and soil depth affect the structure of microbial community, but the effect of soil depth is more significant. Soil nutrients moisture and pH are major contributing soil factors, elevations and climate are major regionally influential factors to the microbial community structure.

The work demonstrated changes in microbial biomass, diversity and populations along the soil profile, illustrated major environmental factors controlling the distribution patterns of soil microbes. The research enriched our theoretical knowledge for microbial geography and the results would direct further work in the research in the functions of soil microbes in farmland.

The results were published entitled as Changes in the Soil Microbial Phospholipid Fatty Aacid Profile with Depth in Three Soil Types of Paddy Fields in China in the international Journal GEODERMA. The work was supported by CAS strategic pilot project (B): Distribution patterns and successions of soil microbes on typical farmland.