Activity and diversity of methane-oxidizing bacteria in glacier forefields on siliceous and calcareous bedrock

[摘要] The global methane (CH₄) cycle is largely driven by methanogenicarchaea and methane-oxidizing bacteria (MOB), but little is known abouttheir activity and diversity in pioneer ecosystems. We conducted a fieldsurvey in forefields of 13 receding Swiss glaciers on both siliceous andcalcareous bedrock to investigate and quantify CH₄ turnover based onsoil-gas CH₄ concentration profiles, and to characterize the MOBcommunity by sequencing and terminal restriction fragment lengthpolymorphism (T-RFLP) analysis of pmoA. Methane turnover was fundamentallydifferent in the two bedrock categories. Of the 36 CH₄ concentrationprofiles from siliceous locations, 11 showed atmospheric CH₄consumption at concentrations of ~1–2 μL L⁻¹ withsoil-atmosphere CH₄ fluxes of –0.14 to –1.1 mg m⁻² d⁻¹.Another 11 profiles showed no apparent activity, while the remaining 14exhibited slightly increased CH₄ concentrations of ~2–10 μL L⁻¹ , most likely due to microsite methanogenesis. Incontrast, all profiles from calcareous sites suggested a substantial, yetunknown CH₄ source below our sampling zone, with soil-gas CH₄concentrations reaching up to 1400 μL L⁻¹. Remarkably, mostsoils oxidized ~90 % of the deep-soil CH₄, resultingin soil-atmosphere fluxes of 0.12 to 31 mg m⁻² d⁻¹. MOB showedlimited diversity in both siliceous and calcareous forefields: allidentified pmoA sequences formed only 5 operational taxonomic units (OTUs) atthe species level and, with one exception, could be assigned to eitherMethylocystis or the as-yet-uncultivated Upland Soil Cluster γ (USCγ).The latter dominated T-RFLP patterns of all siliceous and most calcareoussamples, while Methylocystis dominated in 4 calcareous samples. Members of Upland SoilCluster α (USCα) were not detected. Apparently, USCγ adapted best to the oligotrophic cold climate conditions at the investigatedpioneer sites.

[学科分类] 地球化学与岩石