Effects of Land Conversion on Soil Microbial Community Structure and Diversity in Songnen Plain, Northeast China

To feed the growing human population, natural grasslands are being converted to agricultural use at a massive scale. This conversion may have consequences for soil biodiversity, but its impact on the community assembly of differentially microbial groups remains largely unknown. Here, we selected the three typical land-use types: grassland, arable land (formerly grassland), and forest (formerly grassland) in the Songnen Plain, Northeastern China. Illumina MiSeq high-throughput sequencing technology based on bacterial 16S rRNA and fungal ITS rRNA was used to study the community structures and diversities of soil bacteria and fungi and to explore the drivers of these changes. The results showed that bacterial community diversity did not change after grassland conversion to forest and arable land, but affected bacterial community abundance at the phylum level. Actinomycetes and Proteobacteria were significantly reduced, Acidobacteria were significantly increased, and Gemmatimonadetes and Bacteroidetes were the most abundant in arable land. Land conversion had significant effects on both fungal community diversity and abundance. After the grassland was converted into forest, the fungal community diversity decreased, but the community abundance increased significantly, the Ascomycetes decreased significantly, and Basidiomycetes became the dominant phylum, especially white rot fungi. Interestingly, the fungal community diversity and community abundance increased significantly after grassland was converted to arable land, and the abundance of Zygomycota increased significantly but the dominant phylum was still Ascomycetes. Canonical correlation analysis (CCA) showed pH, MC, NO3--N, TP, AP, and other soil factors are important factors affecting the composition of microbial communities. In the soil of this study area, the composition of bacterial communities is mainly driven by changes in pH and soil texture, and the composition of fungal communities is most closely related to changes in soil nutrient utilization. Changes in land-use patterns have an effect on the structure and diversity of microbial communities by changing the physical and chemical properties of the soil.