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

ABSTRACT

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.

KEYWORDS:

• CO₂ fixation
• microbial autotrophs
• soil microbial biomass
• C cycling
• paddy soil

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was financially supported by the National Natural Science Foundation of China [41430860], [41301275]; International Cooperation and Regional Science and Technology of Hunan Province [2015WK3044]; and the Open Foundation of Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences [ISA2015101].