Positive response of nitrite-dependent anaerobic methane oxidation to both gradual and abrupt increases of atmospheric CO2 concentration in paddy soils

Abstract

The global ongoing increase in the atmospheric CO2 concentration is a gradual rather than an abrupt process. Although the abrupt increase in atmospheric CO2 concentration has been reported to greatly affect nitrite-dependent anaerobic methane oxidation (n-damo), the effect of a gradual increase in atmospheric CO2 concentration on n-damo remains unclear. To better evaluate the role of n-damo in paddy soils, this study investigated the responses of n-damo to different CO2 treatments: the ambient CO2 concentration (CK), a gradual increase (GI), and an abrupt increase (AI) in the CO2 concentration across different growth periods and soil depths. The 13CH4 stable isotope and quantitative PCR results revealed that compared to the CK, GI and AI significantly increased the activity of n-damo by 91.6 % and 90.0 % (p < 0.05), respectively, and also significantly increased the abundance of Candidatus Methylomirabilis oxyfera (M. oxyfera)-like bacteria by 67.7 % and 98.6 % (p < 0.05), respectively. Although there was no significant variation between GI and AI. In addition, the activity and abundance differed significantly between growth period and soil depth. The high-throughput sequencing results showed that GI and AI had little effect on bacterial community, while the soil depth had a significant impact on bacterial community. The changes in several soil physiochemical factors (e.g., the contents of soil water, organic carbon, and inorganic nitrogen) had important impacts on n-damo activity and the bacterial community structure. Overall, the results indicate a positive and similar response of n-damo to both gradual and abrupt increases in the atmospheric CO2 concentration in paddy soils.