Factors Affecting Soil and Rhizosphere Microbial Community Structure in An Agroecosystem.

Soil and rhizosphere microbial community structure is affected by a variety of physical, chemical, climactic, and biological factors, many of which interact with each other. In order to determine the major factors affecting microbial community biomass and structure in an agroecosystem we ran a three-year replicated field experiment using a tomato cropping system with nine treatments: bare soil, black polyethylene, white polyethylene, hairy vetch cover crop, hairy vetch above-ground biomass, hairy vetch below-ground biomass, rye cover crop, rye above-ground biomass, and rye below-ground biomass. Tomato rhizosphere and bulk soil were analyzed by PLFA and TRFLP. Cover cropping increased soil microbial biomass, with both shoots and roots contributing to this effect. Cover cropping altered soil and rhizosphere microbial community structure, resulting in increased proportions of Gram-negative bacteria and fungi and reduced proportions of Gram-positive bacteria. However, the effect of cover crop on community structure during the tomato harvest season was primarily due to changes in soil temperature and moisture rather than direct effects of the cover crop.