1.State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences;2.School of Geography Science, Nanjing Normal University;3.Institute of Soil Science, Chinese Academy of Sciences
The National Natural Science Foundation of China (92251305)
【Objective】CH4 is the second most potent greenhouse gas only next to CO2. Continued CH4 and CO2 emissions by human activities pose a major challenge to the mitigation of global climate change. Rice paddy, a main form of artificial wetland, accounts for ~8% of anthropogenic sources of CH4. The elevated atmospheric CO2 (eCO2) affect the cycling of nutrients and elements in paddy fields mainly through the changes in plant-soil-microbe interactions, which also influence net CH4 flux associated with both the methanogenic and methanotrophic processes. However, how eCO2 affects aerobic methane oxidation in paddy soils has rarely been examined, and the adaptative mechanisms of active methane-oxidizing bacteria (MOB) for eCO2 remain unclear. This study aimed to explore the changes in methane-oxidizing rates and identify the active MOB phylotypes in paddy soil under the eCO2 treatment. 【Method】We collected paddy soil samples from China’s FACE (Free Air CO2 Enrichment) experiment station, with FACE treatment and ambient CO2 concentration treatment (aCO2). The CH4-feeding microcosm incubation was applied to learn the methane-oxidizing rates in the two soils. DNA-based stable isotope probing (DNA-SIP) combined with quantitative polymerase chain reaction (qPCR) of methane-oxidizing functional gene pmoA was used to identify the 13C-labeled DNA. High-throughput sequencing and phylogenetic analysis for the 16S rRNA gene amplicons of the 13C-DNA were used to identify the active microbiomes during methane oxidation. 【Result】The results showed that eCO2 significantly stimulated aerobic methane-oxidizing rate when compared to the ambient CO2 treatment, with 301.8 and 243.3 nmol CH4 g-1 d.w.s hour-1, respectively. The abundance of MOB increased by 1.1~1.2- folds under eCO2. A group of MOB assimilated 13CH4 and synthesized 13C-DNA, which were separated into heavy fractions during DNA-SIP. The result of high-throughput sequencing for 13C-DNA showed that Methylobacter and Methylosarcina predominated the active MOB phylotypes. The relative abundance of Methylobacter increased by 16.2~17.0% while the relative abundance of Methylosarcina decreased under eCO2. eCO2 also stimulated the activity of non-methanotrophic bacteria, such as Acidovorax and Pseudomonas, which implies a methanotrophy-induced microbial community response to eCO2. 【Conclusion】This study reveals positive effects of elevated atmospheric CO2 on aerobic methane oxidation in paddy soil, with the predominant and active MOB of Methylobacter playing crucial roles, indicating an improved potential of methane oxidation under the scenarios of global climate change.