Page 154 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 7. Methane cycling in Arctic thermokarst lake sediments
methanogenesis (Kotsyurbenko 2005b; Wagner et al. 2005; Kotsyurbenko et al. 2007; Blake et
al. 2015; Liebner et al. 2015).
The produced methane diffuses through the sediment column upwards, where it can be (partially) oxidized to CO2 by methanotrophic Archaea and Bacteria. The aerobic methanotrophs in permafrost soils are generally dominated by type I methanotrophs (Gammaproteobacteria) (Trotsenko and Khmelenina 2005; Wagner et al. 2005; Liebner and Wagner 2007; Trotsenko and Murrell 2008; Liebner et al. 2009; Semrau, DiSpirito and Yoon 2010; He et al. 2012; Martinez-Cruz et al. 2017), whilst some other studies found high relative abundance of type II methanotrophs (Alphaproteobacteria) (Knoblauch et al. 2008; Stackhouse et al. 2017). Methanotrophs affiliated with Verrucomicrobia have been detected in permafrost sediments (Hansen et al. 2007; Dan et al. 2014; Ganzert, Bajerski and Wagner 2014; Lansing et al. 2015; Frey et al. 2016). Recently, the potential for anaerobic oxidation of methane (AOM) has been shown in (submarine) permafrost (Overduin et al. 2015; Winkel et al. 2018).
CH4 emissions from natural environments will likely increase by 2100 and beyond (Dean et al. 2018). However, the relative contribution of Arctic microbial methane fluxes to global methane emission remains highly uncertain (Wagner et al. 2017). In order to predict the vulnerability of permafrost carbon to decomposition and the resulting CH4 emission, we need to better understand how Arctic microbial communities respond to realistic warming scenarios and changes in nutrient availability. Identifying the responsible microbial communities is a good starting point in unraveling the microbial diversity and activity, and in quantifying the contribution of thermokarst lakes to the global CH4 budget in a warming world. Here, we investigate the effect of the projected temperature increase (+6°C by 2100 [Myhre et al. 2013]) on the activity and community composition of both CH4-producing and -oxidizing microorganisms in the sediment of two thermokarst lakes in Utqiaġvik, Alaska. The influence of temperature on Arctic microbial communities was assessed by a complementary array of techniques including 16S rRNA gene amplicon sequencing and CH4 flux measurements in batch incubations. We found that both methanogenic and aerobic methanotrophic rates increased with warming. The microbial community composition was shifted in response to the addition of different substrates.
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