Desert soil sequesters atmospheric CO2 by microbial mineral formation

Abstract

Microbial carbonate formation in soil may play a critical role in sequestering atmospheric CO2, specifically in drylands with sparse vegetation and harsh environments. However, few studies have examined the mechanism of CO2 fixation by soil microbes. Here, we investigated the sign of soil inorganic carbon (SIC) formed by microbial populations recovered from soil in the Mu Us Desert and identified the carbon source of this process by tracking the isotope profile of atmospheric CO2 in the SIC pool. In addition, we used high-throughput sequencing to predict the function of soil microbial genes involved in metabolic pathways associated with the formation of carbonaceous minerals, and characterised these minerals using scanning electron microscopy, energy-dispersive X-ray, and X-ray diffraction spectrometry. We found that atmospheric CO2 was incorporated into SIC via microbial processes at a rate of approximately 52.13 μg C kg−1 d−1 during a 2.5-month labelling period under 13CO2, and that microbial genes predicted to function in metabolic pathways for carbonaceous mineral formation were widespread among desert soil microbes. Moreover, the composition of microbial populations, along with the predicted metabolic pathways for microbial mineral formation, correlated significantly with rate of microbial CO2 incorporation into SIC. Importantly, we observed the formation of carbonaceous minerals such as calcite in desert soil samples inoculated with indigenous microbes. To our knowledge, we demonstrated for the first time that desert soil microbes are directly involved in fixing atmospheric CO2 via biomineralisation. Our findings provide empirical evidence for soil microbe-driven sequestration of atmospheric carbon and further reveal the potential capacity of desert soil for carbon sequestration.