High peatland methane emissions following permafrost thaw: enhanced acetoclastic methanogenesis during early successional stages

[摘要] Permafrost thaw in northern peatlands often leads to increased methane(CH 4 ) emissions, but the underlying controls responsible for increasedemissions and the duration for which they persist have yet to be fullyelucidated. We assessed how shifting environmental conditions affectmicrobial communities and the magnitude and stable isotopic signature( δ 13 C) of CH 4 emissions along a thermokarst bog transectin boreal western Canada. Thermokarst bogs develop following permafrost thawwhen dry, elevated peat plateaus collapse and become saturated and dominatedby Sphagnum mosses. We differentiated between a young and a mature thermokarst bogstage ( ∼  30 and ∼  200 years since thaw,respectively). The young bog located along the thermokarst edge was wetter, warmer, and dominated by hydrophilic vegetation compared to the mature bog.Using high-throughput 16S rRNA gene sequencing, we show that microbialcommunities were distinct near the surface and converged with depth, butfewer differences remained down to the lowest depth (160 cm). Microbialcommunity analysis and δ 13 C data from CH 4 surfaceemissions and dissolved gas depth profiles show that hydrogenotrophicmethanogenesis was the dominant pathway at both sites. However, mean δ 13 C-CH 4 signatures of both dissolved gas profiles and surfaceCH 4 emissions were found to be isotopically heavier in the young bog( − 63 ‰ and − 65 ‰, respectively)compared to the mature bog ( − 69 ‰ and − 75 ‰, respectively), suggesting that acetoclasticmethanogenesis was relatively more enhanced throughout the young bog peatprofile. Furthermore, mean young bog CH 4 emissions of 82 mg CH 4  m −2  d −1 were  ∼  3 times greater than the 32 mg CH 4  m −2  d −1 observed in the mature bog. Our study suggeststhat interactions between the methanogenic community, hydrophilicvegetation, warmer temperatures, and saturated surface conditions enhanceCH 4 emissions in young thermokarst bogs but that these favourableconditions only persist for the initial decades after permafrost thaw.

[学科分类] 大气科学