Soil Microbes from Saline-Alkali Farmland Can Form Carbonate Precipitates

The formation of soil inorganic carbon in saline-alkali lands is of great significance for enhancing soil carbon sequestration. As for the formation mechanisms, in addition to the discovered abiotic mechanisms, the microbial mechanisms remain unclear. To address this, soil microbes were isolated from the saline-alkali farmland of the Yellow River Delta in north China. Then, their capacity for carbonate precipitation formation was determined. Ten microbial strains were obtained from the soil. Of these, seven strains (four bacterial strains and three fungal strains), belonging to Rhodococcus sp., Pseudomonas sp., Bacillus sp., Streptomyces sp., Aspergillus sp., Cladosporium sp., and Trichoderma sp., formed carbonate precipitates in the range of 89.77 similar to 383.37 mg. Moreover, the formation of carbonate precipitates was related to specific metabolisms by which microbes can raise the pH (from 7.20 to >8.00), suggesting that soil microbes that can enhance pH values by specific metabolisms containing the function of carbonate formation. Although an in situ experiment is needed to confirm such capacity, these results showed that soil bacteria and fungi existing in the saline-alkali farmland soil can form carbonate precipitates. The present study provided a microbial perspective for the mechanism of soil inorganic carbon formation, further implying a microbial potential of soil carbon sequestration in saline-alkali farmlands.