A pan‐Arctic synthesis of CH₄ and CO₂ production from anoxic soil incubations

Abstract

Permafrost thaw can alter the soil environment through changes in soil moisture, frequently resulting in soil saturation, a shift to anaerobic decomposition, and changes in the plant community. These changes, along with thawing of previously frozen organic material, can alter the form and magnitude of greenhouse gas production from permafrost ecosystems. We synthesized existing methane (CH ) and carbon dioxide (CO ) production measurements from anaerobic incubations of boreal and tundra soils from the geographic permafrost region to evaluate large-scale controls of anaerobic CO and CH production and compare the relative importance of landscape-level factors (e.g., vegetation type and landscape position), soil properties (e.g., pH, depth, and soil type), and soil environmental conditions (e.g., temperature and relative water table position). We found fivefold higher maximum CH production per gram soil carbon from organic soils than mineral soils. Maximum CH production from soils in the active layer (ground that thaws and refreezes annually) was nearly four times that of permafrost per gram soil carbon, and CH production per gram soil carbon was two times greater from sites without permafrost than sites with permafrost. Maximum CH and median anaerobic CO production decreased with depth, while CO :CH production increased with depth. Maximum CH production was highest in soils with herbaceous vegetation and soils that were either consistently or periodically inundated. This synthesis identifies the need to consider biome, landscape position, and vascular/moss vegetation types when modeling CH production in permafrost ecosystems and suggests the need for longer-term anaerobic incubations to fully capture CH dynamics. Our results demonstrate that as climate warms in arctic and boreal regions, rates of anaerobic CO and CH production will increase, not only as a result of increased temperature, but also from shifts in vegetation and increased ground saturation that will accompany permafrost thaw.

Temperature and moisture effects on greenhouse gas emissions from deep active-layer boreal soils

“…Our incubation was fully aerobic, but its results are consistent with the conclusion that respiration in the form of CO 2 is likely to dominate the high-latitude C feedback, and that aerobic soils, and the conditions under which currently waterlogged soils may drain, deserve particular attention. In terms of absolute flux rates, Treat et al (2015) reported mean CO 2 rates of 47 (all mineral soils) and 101 (for 20-100 cm soils) µg C-CO 2 g C −1 day −1 from a pan-Arctic synthesis of anaerobic soil incubations, which is somewhat lower than our aerobic incubation results. Treat et al (2014) also found CO 2 and CH 4 emissions to be strongly correlated with temperature and moisture based on an incubation of Alaskan peats.…”

“…Methane was also a far smaller C flux than CO 2 from these soils, in particular at higher temperatures (as CO 2 was responsive to temperature, but CH 4 was not). This is true more generally: for example, Treat et al (2015) found a median CO 2 : CH 4 production ratio of 387 for anaerobic incu- bations of boreal soils. This is naturally far lower than our observed aerobic (and thus high-CO 2 ) ratios, but nonetheless consistent with them.…”

“…Because the dependent variable (CO 2 or CH 4 flux) was non-normally distributed, it was transformed using a natural-logarithm (+0.1 µg C g C −1 day −1 to ensure all positive fluxes, following Treat et al, 2015) transformation. Soil core was treated as a random effect in the model.…”

“…Laboratory incubations, field observations, and metanalyses have documented changing GHG fluxes with rising temperature (Olefeldt et al, 2013;Davidson and Janssens, 2006;Hashimoto et al, 2015;Treat et al, 2015). GHG responses to wetting and thawing dynamics exhibit substantial variability between studies, probably due to differences in soil type, antecedent conditions, phase changes, experimental protocols, etc.…”

Thermo-erosion gullies boost the transition from wet to mesic tundra vegetation

“…Wetlands serve as preferred grounds for Arctic herbivores such as snow geese (Gauthier et al, 1996;Massé et al, 2001;Doiron et al, 2014). They are also expected to produce more methane compared to shrub-dominated areas (Olefeldt et al, 2013;Nauta et al, 2015;Treat et al, 2015).…”