Microbial assimilation of atmospheric CO2 into soil organic matter revealed by the incubation of paddy soils under 14C-CO2 atmosphere

Similar to higher plants, microbial autotrophs possess photosynthetic systems that enable them to fix CO₂. To measure the activity of microbial autotrophs in assimilating atmospheric CO₂, five paddy soils were incubated with ¹⁴C-labeled CO₂ for 45 days to determine the amount of ¹⁴C-labeled organic C being synthesized. The results showed that a significant amount of ¹⁴C-labeled CO₂ incorporated into microbial biomass was soil specific, accounting for 0.37%–1.18% of soil organic carbon (¹⁴C-labeled organic C range: 81.6–156.9 mg C kg^?1 of the soil after 45 days). Consequently, high amounts of C-labeled organic C were synthesized (the synthesis rates ranged from 86 to 166 mg C m^?2 d^?1). The amount of atmospheric ¹⁴CO₂ incorporated into microbial biomass (¹⁴C-labeled microbial biomass) was significantly correlated with organic C components (¹⁴C-labeled organic C) in the soil (r = 0.80, p < 0.0001). Our results indicate that the microbial assimilation of atmospheric CO₂ is an important process for the sequestration and cycling of terrestrial C. Our results showed that microbial assimilation of atmospheric CO₂ has been underestimated by researchers globally, and that it should be accounted for in global terrestrial carbon cycle models.