Soil microbial communities are affected more by land use than seasonal variation in restored grassland and cultivated Mollisols in Northeast China

Seasonal variations of soil microbial communities in a cultivated black soil (0–20 cm) with different fertilizing treatments [no fertilizer (NoF), chemical fertilizer (CF) and chemical fertilizer plus manure (CFM)] and in a neighboring plot of natural restoration (NR) in Northeast China were studied over a period of two years. The cultivated soils were plowed and had a rotation of maize–soybean–wheat. The NR plot was revegetated naturally with grasses since 1985. The soil microbial biomass C content across the five sampling times was 102, 89, and 53% larger in NR plot than that in NoF, CF, and CFM plots, respectively. Dominant members of bacterial and fungal communities as assessed by DGGE banding patterns of partial PCR products of bacterial 16S rDNA and fungal rDNA ITS were different between cultivated plots and NR plot but not between cultivated plots, and less influenced among seasonal sampling times. These findings indicate that land use was a major factor in influencing dominant members of microbial communities in black soils in Northeast China and that they were little affected by fertilization and very stable over time despite the distinct seasonal fluctuations in temperature and rainfall. Sequence analysis of several excised DGGE bands indicated that bacterial phyla of Proteobacteria and Actinobacteria, and fungal phyla of Ascomycetes and Basidiomycetes contributed to the dominant microbial community members in black soils in Northeast China.

► 21-year long-term of natural restoration increased soil microbial biomass carbon.
► Microbial communities differed between restored grassland and cultivated black soils.
► Seasonal changes of microbial communities are associated with plant growth.
► The effect of fertilization on microbial communities was no obvious in black soils.