Methane Production Pathway Regulated Proximally by Substrate Availability and Distally by Temperature in a High‐Latitude Mire Complex

Abstract

Projected 21st century changes in high‐latitude climate are expected to have significant impacts on permafrost thaw, which could cause substantial increases in emissions to the atmosphere of carbon dioxide (CO2) and methane (CH4, which has a global warming potential 28 times larger than CO2 over a 100‐year horizon). However, predicted CH4 emission rates are very uncertain due to difficulties in modeling complex interactions among hydrological, thermal, biogeochemical, and plant processes. Methanogenic production pathways (i.e., acetoclastic [AM] and hydrogenotrophic [HM]) and the magnitude of CH4 emissions may both change as permafrost thaws, but a mechanistic analysis of controls on such shifts in CH4 dynamics is lacking. In this study, we reproduced observed shifts in CH4 emissions and production pathways with a comprehensive biogeochemical model (ecosys) at the Stordalen Mire in subarctic Sweden. Our results demonstrate that soil temperature changes differently affect AM and HM substrate availability, which regulates magnitudes of AM, HM, and thereby net CH4 emissions. We predict very large landscape‐scale, vertical, and temporal variations in the modeled HM fraction, highlighting that measurement strategies for metrics that compare CH4 production pathways could benefit from model informed scale of temporal and spatial variance. Finally, our findings suggest that the warming and wetting trends projected in northern peatlands could enhance peatland AM fraction and CH4 emissions even without further permafrost degradation.

Controls on Soil Organic Matter Degradation and Subsequent Greenhouse Gas Emissions Across a Permafrost Thaw Gradient in Northern Sweden

“…Although the ecological roles and properties of resource generalists and specialists in many discontinuous permafrost areas have been examined via extensive metagenomic and metatranscriptomics analysis (Liao et al, 2016;Sriswasdi et al, 2017;Singleton et al, 2018;Woodcroft et al, 2018), highly resolved molecular characterization of the OM is an essential foundation upon which we can understand ecosystem C cycling by both plants and microbes in peatlands for predicting future changes in CO 2 and CH 4 production potential (Qualls and Richardson, 2003). Moreover, current models for estimating permafrost soil carbon loss rates are lacking representations of key microbial processes that control OM transformations, leading to enormous uncertainty in model simulations (Burke et al, 2012;Koven et al, 2015;Chang et al, 2019). At most, such models only include a quantitative measure of OM concentration (Lucchese et al, 2010) but neglect the fact that the rate of OM degradation is dependent on the abundance and diversity of active microbes and OM quality and diversity.…”

Functional Representation of Biological Components in Methane‐Cycling Processes in Wetlands Improves Modeling Predictions

“…The results from Chang et al (2019) may also have far-reaching implications beyond the permafrost-thawing areas. Tropical peatlands are among the largest wetland sources of methane, despite covering a Figure 1.…”

“…Such understanding is even more relevant to rapid-changing wetland environments, such as peatlands in boreal regions, where permafrost thawing is shifting plant communities (from a bog-to fen-like vegetation) and, hence, the primary substrates for methanogenesis. Chang et al (2019) used the ecosys model to show how the changes to the type of vegetation resulting from persistent permafrost thawing drive shifts in the methanogenesis pathway (i.e., AM or HM), substrate composition, and the magnitude in methane emissions and modulate their sensitivity to temperature change. Along with the vegetation shift, soil temperature increases in fens, which, in turn, increases biological activity and, consequently, net emissions from both the AM and HM pathways.…”

“…VILLA measurements and geographical coverage. Then, a mechanistic approach based on plant functional types, analogous to Chang et al (2019) approach to methanogenesis, could be a reasonable compromise between model enhancement and degrees of freedom. Further work will be needed to elucidate if such an avenue is feasible and the parameters that better describe each plant functional type.…”

“…The ecosys model (Grant et al, 2017), a comprehensive biogeochemical model, is one the few models capable of integrating most of these processes simultaneously and robustly represents the two main methanogenic pathways involved in methane production (i.e., acetoclastic methanogenesis [AM] and hydrogenotrophic methanogenesis [HM]) ( Figure 1). Although laboratory experiments have shown how different biophysical factors may influence the methanogenic pathways, simulations performed with ecosys by Chang et al (2019) provide, for the first time, a valuable insight on how temperature may be changing methane production in a high-latitude peatland at a landscape scale.…”