Abstract
ABSTRACTMethane production in thawing permafrost can be substantial, yet often evolves after long lag phases or is even lacking. A central question is to which extent the production of methane after permafrost thaw is determined by the initial methanogenic community. We quantified the production of methane relative to carbon dioxide (CO2) and enumerated methanogenic (mcrA) gene copies in long-term (2–7 years) anoxic incubations at 4 °C using interglacial and glacial permafrost samples of Holocene and Pleistocene, including Eemian, origin. Changes in archaeal community composition were determined by sequencing of the archaeal 16S rRNA gene. Long-term thaw stimulated methanogenesis where methanogens initially dominated the archaeal community. Deposits of interstadial and interglacial (Eemian) origin, formed under higher temperatures and precipitation, displayed the greatest response to thaw. At the end of the incubations, a substantial shift in methanogenic community composition and a relative increase in hydrogenotrophic methanogens had occurred except for Eemian deposits in which a high abundance of potential acetoclastic methanogens were present. This study shows that only anaerobic CO2 production but not methane production correlates significantly with carbon and nitrogen content and that the methanogenic response to permafrost thaw is mainly constrained by the paleoenvironmental conditions during soil formation.
Highlights
Up to about 1300 Pg of carbon is stored in northern terrestrial landscapes affected by permafrost, which is more carbon than currently in the atmosphere (Hugelius et al 2014)
We address the following hypotheses: (i) The development of methane production after long-term permafrost thaw is determined by the initial methanogenic community size and composition and (ii) methanogenic abundance, community composition and diversity change substantially in response to long-term permafrost thaw
The time period before methane production began- defined as the lag phase- lasted 230–2395 days and was shortest in the Eemian deposits (230– 387 days)
Summary
Up to about 1300 Pg of carbon is stored in northern terrestrial landscapes affected by permafrost, which is more carbon than currently in the atmosphere (Hugelius et al 2014). Permafrost underlies a shallow layer of surface soil (the active layer), which thaws during the short summer season. Permafrost environments are often characterized by waterlogged soils as a result of restricted surface drainage caused by the underlying, permanently frozen ground. A 25% loss of the current permafrost area is predicted to occur in the 100 years due to warming-induced thaw (Deng et al 2014). The mobilization of carbon due to permafrost thaw, the associated release of GHG and their radiative forcing constitute the permafrost carbon feedback to climate change (PCF) (Schuur et al 2015), which is predicted to cause global warming of up to 0.4◦C by the year 2300 (Schneider von Deimling et al 2015)
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