Methanogenesis in oxygenated soils is a substantial fraction of wetland methane emissions

Abstract

The current paradigm, widely incorporated in soil biogeochemical models, is that microbial methanogenesis can only occur in anoxic habitats. In contrast, here we show clear geochemical and biological evidence for methane production in well-oxygenated soils of a freshwater wetland. A comparison of oxic to anoxic soils reveal up to ten times greater methane production and nine times more methanogenesis activity in oxygenated soils. Metagenomic and metatranscriptomic sequencing recover the first near-complete genomes for a novel methanogen species, and show acetoclastic production from this organism was the dominant methanogenesis pathway in oxygenated soils. This organism, Candidatus Methanothrix paradoxum, is prevalent across methane emitting ecosystems, suggesting a global significance. Moreover, in this wetland, we estimate that up to 80% of methane fluxes could be attributed to methanogenesis in oxygenated soils. Together, our findings challenge a widely held assumption about methanogenesis, with significant ramifications for global methane estimates and Earth system modeling.

Comparative genomics and physiology of the genus Methanohalophilus, a prevalent methanogen in hydraulically fractured shale

“…While Methanohalophilus have been found in the six unconventional reservoirs plays sampled to date, other methanogens including Methanolobus and Methanoplanus have been occassionally detected (Murali Mohan et al, ; Daly et al, ). Consistent with other methanogenic ecosystems (Gill et al, ; Henderson et al, ; Angle et al, ), the relative abundance of methanogens in unconventional reservoirs is generally low, typically less than 7% (Fig. C).…”

Wetland methane emissions dominated by plant‐mediated fluxes: Contrasting emissions pathways and seasons within a shallow freshwater subtropical wetland

“…Within wetlands, biogenic CH 4 is produced by methanogenic archaea as a by‐product of the decomposition of organic matter, under suitable environmental conditions. Generally, CH 4 production is favored within anoxic waterlogged habitats and sediments (typical of wetlands), whereas oxygenated habitats favor aerobic respiration and CO 2 production (Whiting and Chanton ); however, recent work suggests that methanogenesis can also occur under oxic conditions (Keppler et al ; Angle et al ; Donis et al ).…”

Widespread methane formation byCyanobacteriain aquatic and terrestrial ecosystems

“…2 and Fig. S2) and while methanogenic Archaea were recently reported from oxic environments (Angle et al, 2017), their activity is attributed to anoxic microniches. Third, sequencing analysis of non-axenic cultures and quantitative real-time PCR of the mcrA gene showed methanogenic Archaea are either absent or present in negligible numbers (Fig.…”