Microbial mediation of soil organic carbon fractions and its feedback to long-term climate change

Abstract

Aims

Understanding the long-term effects of elevated atmospheric CO₂ (eCO₂) and warming on soil organic carbon (SOC), along with the microbial mechanisms involved, is important for predicting SOC stability in the context of future climate change.

Methods

Open-top chambers were used to simulate an increase in the atmospheric CO₂ concentration to 700 ppm (eCO₂) and an air temperature of 2 °C above the ambient temperature (warming) in a six-year experiment to examine the effects of eCO₂ and warming on the SOC fractions and bacterial community diversity. Maize plants were grown in four major farming soils, namely, Phaeozem, Kastanozem, Fluvisol and Acrisol.

Results

Six years of eCO₂ did not increase the SOC concentration in any soil but altered the distribution of the SOC fractions. In comparison, eCO₂ and warming decreased fine particulate organic C (fPOC) but increased the mineral-associated organic C (MOC) concentrations in Phaeozem and Kastanozem. In comparison, eCO₂ and warming significantly decreased the MOC in Fluvisol and tended to increase it in Acrisol. For Phaeozem, Kastanozem and Acrisol, fPOC was negatively correlated with MOC (p < 0.05). Warming altered the bacterial community composition in Kastanozem, Acrisol and Fluvisol. The increased abundance of Aquicella in Fluvisol under eCO₂ and warming was associated with accelerated MOC decomposition.

Conclusions

Long-term eCO₂ and warming might not alter the SOC stock but affect the bacterial community, accelerating C turnover among different SOC pools. The decrease in the MOC fraction of Fluvisol raises concerns about the SOC sustainability of this soil under climate change.