Structure of functional ecological networks of soil microbial communities for nitrogen transformations and their response to cropping in major soils in eastern China

Abstract

It is well established that nitrogen cycling in agricultural soil-plant systems greatly affects productivity and the environment. However, the impact of microbial interactions on nitrogen cycling and its response to management practices such as cropping and fertilization remain unclear. In this study, three typical soils were selected (a black soil located in the cold temperate region, a Chao soil in the warm temperate region and a red soil in the middle subtropical region) along a North-South transect of eastern China, and a controlled field experiment was set up with non-cropping (bare soil) and cropping (planting maize) treatments. The core microbial communities (with members shared across different habitats) associated with N transformations were identified from high-throughput functional gene array hybridization data. Functional molecular ecological networks (fMENs) were then developed by a random matrix theory (RMT)-based conceptual framework. Cropping increased the richness of most N transforming core genes and the complexity of N transforming fMENs. The number of modules in the topological structure of fMENs increased from eight under non-cropping to 28 under the cropping treatment. Two module hubs (key genes) of the nitrogen fixation gene ( nifH ) were present under the non-cropping treatment, and nine module hubs including the nitrogen fixation gene ( nifH ) and the denitrification genes ( narG and nosZ ) were present under the cropping system. Additionally, changes in the network structure were significantly correlated with plant, climate and soil variables. In conclusion, agricultural management practices and environmental changes can alter the network interactions in soil microbial communities, and consequently affect their nutrient cycling functions.