Significance Given the current pressing need to more fully understand the methane cycle on Earth, in particular, unidentified sinks for methane, identifying and quantifying novel sinks for methane is fundamental importance. Here, we provide previously unidentified direct evidence for the nitrite-dependent anaerobic methane oxidation (n-damo) process as a previously overlooked microbial methane sink in wetlands by stable isotope measurements, quantitative PCR assays, and 16S rRNA and particulate methane monooxygenase gene clone library analyses. It is estimated that n-damo could consume 4.1–6.1 Tg of CH 4 m −2 per year in wetlands under anaerobic conditions, which is roughly 2–6% of current worldwide CH 4 flux estimates for wetlands. Given the worldwide increase in nitrogen pollution, this methane sink may become more important in the future.

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BackgroundPaddy soil dissolved organic matter (DOM) represents a major hotspot for soil biogeochemistry, yet we know little about its chemodiversity let alone the microbial community that shapes it. Here, we leveraged ultrahigh-resolution mass spectrometry, amplicon, and metagenomic sequencing to characterize the molecular distribution of DOM and the taxonomic and functional microbial diversity in paddy soils across China. We hypothesized that variances in microbial community significantly associate with changes in soil DOM molecular composition.ResultsWe report that both microbial and DOM profiles revealed geographic patterns that were associated with variation in mean monthly precipitation, mean annual temperature, and pH. DOM molecular diversity was significantly correlated with microbial taxonomic diversity. An increase in DOM molecules categorized as peptides, carbohydrates, and unsaturated aliphatics, and a decrease in those belonging to polyphenolics and polycyclic aromatics, significantly correlated with proportional changes in some of the microbial taxa, such as Syntrophobacterales, Thermoleophilia, Geobacter, Spirochaeta, Gaiella, and Defluviicoccus. DOM composition was also associated with the relative abundances of the microbial metabolic pathways, such as anaerobic carbon fixation, glycolysis, lignolysis, fermentation, and methanogenesis.ConclusionsOur study demonstrates the continental-scale distribution of DOM is significantly correlated with the taxonomic profile and metabolic potential of the rice paddy microbiome. Abiotic factors that have a distinct effect on community structure can also influence the chemodiversity of DOM and vice versa. Deciphering these associations and the underlying mechanisms can precipitate understanding of the complex ecology of paddy soils, as well as help assess the effects of human activities on biogeochemistry and greenhouse gas emissions in paddy soils.Electronic supplementary materialThe online version of this article (10.1186/s40168-018-0561-x) contains supplementary material, which is available to authorized users.