The effect of microorganisms on soil carbonate recrystallization and abiotic CO2 uptake of soil

Abstract

Desert ecosystems with a high soil pH are considered as a sink for atmospheric CO2. Although high CO2-uptakevia chemical processes is the major CO2-uptake process in saline and alkaline soil, microorganisms may affect the exchange of inorganic carbon between the soil solution and the solid phase. Some studies related to microbial processes on carbonate formation have been published, but seldom focus on saline and alkaline soils. To determine the microbial effects on the inorganic C flux and CaCO3 recrystallization, sterile and non-sterile Solonchak samples were incubated in a 14CO2-labelled atmosphere at two CO2 concentrations (0.2% and 2%). The 14C activity was measured in the soil solution, air, and in CaCO3 after 2, 7, 21, 92 and 197 days. The 14C in dissolved organic carbon in the sterile and non-sterile soils was below 5% of the 14C input. 14C trapping in CaCO3 increased with the decrease of the 14C remaining in the gaseous CO2. Carbonate recrystallization increased logarithmically with time (R2 > 0.96). A two percent initial CO2 concentration lead to higher CaCO3 recrystallization (5–50 × 10−3% of initial CaCO3) compared to a 0.2% initial CO2 concentration (0.8–7 × 10−3% of initial CaCO3) from 2 to 197 days. CaCO3 recrystallization (% of initial CaCO3) in the sterile Solonchak was higher by 10% to 190% than the non-sterile Solonchak, indicating that the microorganisms decreased the 14C trapping of CaCO3 by 4–23% from 2 to 197 days. We assume that microorganisms grew on the carbonate surface like a coating. This must have retarded the carbonate recrystallization. We concluded that the soil CO2 concentration is the most important factor for CaCO3 recrystallization. The presence of microorganisms strongly decreased the CaCO3 recrystallization. CaCO3 recrystallization process including CO2 in soil water could be the abiotic CO2 uptake from the atmosphere by saline and alkaline soil.