Development of soil food web of microbes and nematodes under different agricultural practices during the early stage of pedogenesis of a Mollisol

Abstract

Agricultural practices such as tillage and organic amendment influence development of the soil food web. However, such effects are not well understood at the initial stage of soil formation. Using an eight-year field experiment established on exposed parent materials of a Mollisol, the objectives of this study were: (1) to determine the effects of agricultural practices on soil food web structure in comparison to the structures of soil nematode guilds and microbial communities, per se; (2) to elucidate the development of the food web of the young soils in relation to parent materials and a mature Mollisol; and (3) to identify the controlling factors of such relationships. The microbial biomass expressed in phospholipid fatty acids and the abundance of nematode guilds increased in the field treatments compared with parent materials by a larger magnitude in Gram positive (G+) bacteria and plant parasite (PP) nematodes under perennials than under cropping. The abundance of bacterivorous (Ba) nematode guilds was significantly correlated with microbial biomass of total bacteria, but not with that of G+ or G− bacteria. The abundance of total Ba, particularly Ba1 nematode guilds was positively correlated with soil organic carbon and its related nutrient contents. Redundancy analysis showed that the structure of food web was similar to nematode guild structure rather than to soil microbial community structure among the soils. The food web structure was separated between the soils under perennials and those under cropping via Axis 1 and between fertilized and not fertilized soils irrespective of land uses via Axis 2. The separations via Axis 1 were mainly driven by PP nematodes in association with high C:N soils, suggesting the determinant effect of land use type, while the separations via Axis 2 were driven by Ba nematodes and bacteria in association with soil physical and chemical properties, indicating the role of soil carbon and nutrients. The food web in the arable soils with more organic amendments was similar to that of mature Mollisol. These findings suggest that soil food web at the early pedogenesis can develop quickly with restoration practices and the development was more affected by land use type than by soil management practices.