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

Abstract

ABSTRACTSimilar 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.