CH4是仅次于CO2的第二大温室气体，而稻田是CH4的主要排放源，未来大气CO2浓度升高情景下(elevated CO2，eCO2)，水稻土好氧甲烷氧化过程及其功能微生物群落适应规律尚不清楚。依托中国FACE(Free Air CO2 Enrichment)水稻田试验平台，通过13C-CH4示踪的室内微宇宙培养实验，采用稳定性同位素核酸探针(DNA-S1P)和高通量测序技术，研究未来大气CO2浓度升高对水稻土甲烷氧化活性及其功能微生物的影响规律。结果表明:与常规大气CO2浓度(ambient CO2，aCO2)相比，eCO2条件下的甲烷氧化活性显著增加，从243 nmol·g-1 d。w。s·h-1增加至302 nmol·g-1 d。w。s·h-1，增幅高达24。3％，甲烷氧化菌数量则增加了 1。1倍～1。2倍。通过超高速离心获得活性甲烷氧化菌同化13CH4后合成的13C-DNA，高通量测序发现，未来大气CO2升高情景下水稻土活性好氧甲烷氧化微生物群落极可能发生明显演替，与对照相比，类型Ⅰ甲烷氧化菌甲基杆菌属Methylobacter的相对丰度增加16。2％～17。0％，而甲基八叠球菌属Methylosarcina的相对丰度下降4。7％～11。1％;同时刺激了食酸菌属Acidovorax和假单胞菌属Pseudomonas等非甲烷氧化菌的活性。综上所述:未来大气CO2升高情景下，水稻土好氧甲烷氧化微生物群落结构发生分异，促进了甲烷氧化通量，而甲烷氧化的代谢产物可能引发土壤中微生物食物网的级联反应，是土壤碳储存和周转的重要功能微生物群。
The Adaptative Mechanisms of Methane-Oxidizing Bacteria for Elevated Atmospheric CO2 in Paddy Soil
[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)affects the cycling of nutrients and elements in paddy fields mainly through the changes in plant-soil-microbe interactions,which also influences 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 302 and 243 nmol CH4·g-1 d.w.s·h-1,respectively.The abundance of MOB increased by 1.1 folds-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.
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