Bacterial community structure of reclaimed soil and its relationship with soil fertility

Abstract: Reclaimed soil can be utilized to quickly and effectively produce under reasonable manual intervention. This study aims to clarify the influence of the reclamation on soil microorganisms in the Lianghuai coal mine area. The coal gangue filling reclaimed soil was also taken as the research object in the field investigation and sampling. Illumina MiSeq high-throughput sequencing was used to analyze the V4 region of specific gene fragments of soil bacteria. Biodiversity was then explored to clarify the soil bacterial community and the response to soil fertility using non-metric multi-dimensional scale analysis, redundancy analysis, variance analysis, fertility index, and regression. The results show that there was no significant effect of reclamation directions on the distribution of bacterial dominant communities from the composition, but there were different proportions of reclamation directions. Specifically, Proteobacteria (32.42%-42.97%), Acidobacteria (10.47%- 15.87%), Actinobacteria (8.90%-18.28%) were the main dominant bacteria groups. Among them, Proteobacteria occupied the most, accounting for more than 30%. Alpha diversity demonstrated that there was no significant difference in the abundance and diversity of bacterial soil samples in different reclamation directions. Some indexes also maintained stable, where the Shannon_Wiener index ranged from 6.19 to 6.85, while Chao1 index ranged from 3131.97 to 4938.37, and the Pielou index of each sample fluctuated around 0.8. Beta diversity analysis showed that there was also no significant difference in the composition of bacterial communities in different reclamation directions. Furthermore, the composition of soil bacterial communities was negatively correlated with the soil depth. The composition of soil bacteria was attributed to different living conditions in the top, middle, and bottom soil layers, such as moisture, aeration, temperature, and nutrients. The pH value was consistent with the change of the diversity index, indicating only a slight influence on the dominant microbial flora and biodiversity. A one-way analysis of variance was carried out on the soil fertility indexes of reclamation directions. It was found that the content of fertility indexes in the surface soil was much higher than that in the bottom soil in general. The fertility quality was evaluated in the order of the cultivated land > grassland > forest, where the cultivated land performed the best reclamation direction. The redundancy analysis showed that the TN, SOM, AP, and AK were the main fertility factors to determine the composition of soil bacterial communities. But some dominant bacterial communities presented no response to the fertility factors, due to the high complexity of the soil microbial community and the regional conditions. The regression model showed that the soil fertility index was positively correlated with the relative abundance of the Thaumarchaeota (P<0.01), and the Streptomyces was negatively correlated (P<0.05). Moreover, there was no strong correlation with the main dominant phylum, due to the complexity of the soil environment of the coal gangue reclaimed land. Consequently, the relative abundance of Thaumarchaeota and Streptomyces can be selected as important biological indicators to evaluate soil fertility, according to the linear regression and the functional effects of Thaumarchaeota and Streptomyces. The finding can also provide strong theoretical support to improve the fertility and quality of the reclaimed soil with the gangue at the microbial level in the Lianghuai mining area.