Impact of land reclamation on the carbon sequestration potential of soil microorganisms in the disturbed mining area of eastern plain

In the eastern plain, the reclaimed soil has been affected by the high underground water level in the mining area, and then the soil always presents to be alkaline and barren. As it is well known that the carbon-fixing bacteria could effectively improve soil nutrients, so they might be useful for the poor reclaimed soil. However, it is still not very clear that how reclamation regulates the carbon fixation capacity of microorganisms and its mechanism. In this study, the eight, fourteen and seventeen-years reclamation samples from the Dongtan Mine in Zoucheng, Shandong, China, were selected as the research objects, as well as the control samples. The variation of six carbon-fixation related bacteria phyla, and twelve carbon fixation genes were explored through Geochip and high-throughput sequencing technology. The results show that:(1) The values of soil pH,dissolved organic carbon, soil β-glucosidase and catalase activities of the reclaimed soil are significantly higher than those of control soil samples(P<0.01). The soil organic carbon, microbial biomass carbon content, and polyphenol oxidase activity are significantly higher in the 17 years reclaimed soil, when compared to the control samples. The effect of reclamation time on soil properties presented is extremely significant(P<0.001);(2) The signal intensity of 12 carbon-fixing genes have been increased with the increasing reclamation years. For the 17-years reclamation samples, the data have been higher than or equal to the control. The 12 carbon-fixing genes are mainly distributed in phyla of Acidobacteria,Actinobacteria,Bacteroidetes,Cyanobacteria,Firmicutes and Proteobacteria; and(3) the abundances of carbon-fixing bacteria are significantly correlated with soil pH,dissolved organic carbon, β-glucosidase, polyphenol oxidase, and catalase activities(P < 0.05). There is also a certain correlation between the signal intensity of most carbon fixation genes and the environmental factors, such as soil pH,microbial biomass carbon, dissolved organic carbon and catalase activity. Reclamation activities could affect the composition of abundant and rare carbon-fixing bacteria, as well as the abundance of functional genes. There might be an effective way to enhance the carbon-fixing ability of reclaimed soils and carbon sinks, through regulating the related environmental factors, for example, soil pH value, microbial biomass carbon or polyphenol oxidase enzyme activity, and so on.