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

<p dir="ltr">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. </p><p dir="ltr">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. </p><p dir="ltr">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. </p><p dir="ltr">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.</p>