Page 219 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

together with less labile organic matter degradation (Buitrón et al. 2014; Yang et al. 2017). Similar observations in long-term anoxic incubations were made before (Holm et al. 2020) and also studies on ice-rich Yedoma deposits have shown that acetate is a less relevant substrate in permafrost deposits exposed to long-term anoxia (Ewing et al. 2015).
Unlike methanogenic archaea, Bathyarchaeia showed an overall increase in the course of the long-term warming scenario while Thaumarchaeota were overall poorly abundant. The phylum of Bathyarchaeia represents an evolutionary diverse microbial group that is found in a wide range of organic-rich environments (Evans et al. 2015). Interestingly, the recent discovery of the growth of Bathyarchaeota subgroup 8 (Bathy-8) on lignin suggests they can play a key role in the degradation of less labile plant organic matter fractions (Yu et al. 2018). In addition, genomic and enzymatic analysis of several Bathyarchaeal lineages showed their capacity for acetogenesis and fermentation of a wide range of organic substrates, including cellulose and aromatic compounds (He et al. 2016; Lazar et al. 2016). Thaumarchaeota are linked to aerobic NH4 oxidation (Kits et al. 2017). They are abundantly detected in environments with low ammonia concentrations, like permafrost, where they can provide an important role in the nitrogen cycle (Pester, Schleper and Wagner 2011; Auguet and Casamayor 2013; Jansson and Taş 2014).
In conjunction with the pronounced changes in GHG production potentials and microbial community structure, we observed large changes in the microbial metabolic potential. Overall, 9 we observed a decrease in both methanogenic and carbon fixation genes, although the acsC
gene encoding the gamma subunit of the CODH/ACS complex involved in the Wood- Ljungdahl pathway increase substantially in TL. The overall decrease in carbon cycling genes
aligns with the decrease in GHG production rates that were observed after long-term incubation
even though gene abundance cannot be directly linked with GHG fluxes.
Studies on permafrost soils have shown a lower abundance of nitrogen cycling genes for permafrost compared to the active layer (Yergeau et al. 2010; Frank-Fahle et al. 2014). However, little is known on the functional response of the communities of the different layers upon thaw. The study by Mackelprang et al. (2011) on permafrost from Hess Creek, Alaska did observe rapid thaw responses for nitrogen and carbon cycle genes. However, data on changes
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