Exploring the response of West Siberian wetland methane emissions to future changes in climate, vegetation, and soil microbial communities

Abstract. We ran the VIC land surface model over the West Siberian Lowland (WSL), forced with outputs from 32 CMIP5 models for the RCP4.5 scenario, and compared the effects of changes in climate and vegetation (leaf area index in particular) on predicted wetland CH₄ emissions and other fluxes for the period 2071–2100, relative to the period 1981–2010. We also explored possible responses of soil microbial communities to these changes. Our results suggest that, if soil microbial communities acclimatize to elevated temperatures without changes in species abundances, end-of-century CH₄ emissions from the WSL will only rise to 3.6 Tg CH₄ yr⁻¹ (6% above historical emissions). In contrast, if microbial species abundances in the north additionally shift to resemble those in the south, CH₄ emissions will more than double, to 7.3 Tg CH₄ yr⁻¹. Crucially, while historical emissions were concentrated in the southern half of the domain, acclimatization plus microbial population shifts concentrate almost 3/4 of future emissions in the northern half of the domain, where the possible release of carbon with permafrost thaw is a concern. In addition, microbial population shifts disproportionately increase microbial activity in the period during and immediately following snowmelt, when highly labile carbon is first thought to be released from the soil. This work indicates the importance of better constraining the responses of soil microbial communities to changes in climate and vegetation as they are critical determinants of the region's future methane emissions.