Changes of the organic carbon content and stability of soil aggregates affected by soil bacterial community after afforestation

Soil aggregation is one of the most important factors affecting soil organic carbon (SOC) stabilization, and the stability of aggregates depends in part on soil microbial diversity and composition. Interactions between the soil bacterial community and SOC content in soil aggregates after afforestation are poorly understood. In this study, we investigated difference in the diversity of soil bacterial with high-throughput 16S rRNA sequencing, as well as the SOC content in soil aggregates representing a chronosequence of 42, 27, and 17 years of Robinia pseudoacacia L. succession (RP42, RP27, and RP17), and in farmland (FL) soil for comparison (millet (Setaria italica) and soybean (Glycine max) rotation).The SOC content in RP17, RP27, and RP42 plots were significantly higher than that of FL by an average of 85.57%, 142.37%, and 76.69% in large macro-aggregates ( > 1 mm), small macro-aggregates (0.25-1 mm), and micro-aggregates ( < 0.25 mm), respectively. The Simpson index for the FL plot was significantly higher than that of the RP17, RP27, and RP42 plots, whereas the Shannon index followed the opposite trend. The dominant bacterial phyla detected were Proteobacteria, Acidobacteria, and Actinobacteria in each afforested and FL sites. These data revealed significant correlations between soil aggregate characteristics, such as SOC content, mean weight diameter (MWD), and geometric mean diameter (GMD), with the relative abundance of Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, Gemmatimonadetes, Nitrospirae, Verrucomicrobia, and Planctomycetes. These relationships suggested that the effects of afforestation on SOC stabilization in soil aggregates are modulated by both soil aggregate size and also soil bacterial diversity. We demonstrate that the interaction between soil aggregate size and soil microbes might be a key factor in effective soil conservation, restoration, sustainability of agroecosystems, and erosion prevention.