Boreal peatlands are simultaneously important ecosystems for terrestrial carbon storage as well as large sources of the greenhouse gas methane. Methanogenic Archaea are thought to primarily use acetoclastic (acetate), hydrogenotrophic (carbon dioxide and hydrogen) or methylotrophic (C-1 compounds) as substrates for pathways to produce methane. Recently, an organism using Methoxylated Aromatic Compounds (MACs) to produce methane was characterized from coal bed systems, however the prevalence, ecology and detailed mechanisms of such organisms and pathways remains unknown. We hypothesized MACs could fuel methanogenesis in peatland ecosystems as MACs are common in peat. We thus conducted microcosm experiments using peat samples collected from Minnesota, USA. Six different methoxylated aromatic compounds were added at various concentrations to 10 grams of peat from various depths in the peat profile, and were incubated anaerobically for up to 100 days. Gas headspace was monitored for CH4 and CO2 using GC methods. At the end of the experiment, samples were harvested and extracted for DNA analysis of 16S rRNA genes using Illumina amplicon and metagenomic sequencing to investigate the microbial communities putatively involved in MAC based methanogenesis.
Results/Conclusions
Our experiments to date show a high degree of heterogeneity in gas production in response to MAC amendment across peat core origins, as well as variation with depth within core profiles. Rates of methanogenesis were generally slow, but significantly increased over the course of the incubation period (up to 0.94 ug C-CH4 / g peat per day vs. 0.26 in controls), as did the CH4:CO2 ratio of headspace gases (up to 12.82 vs. 0.96 in controls), and were highest with 2-methoxyphenol, 1,3,5-trimethoxybenzene, and 3,4,5-trimethoxybenzyl alcohol additions. By the end of the incubations, several MAC incubations produced significantly more methane than no-substrate controls or the methanol and trimethylamine compounds used as comparators. Together our results to date suggest that MAC utilizers are present in peatland systems, but may be in low abundance, and that high concentrations of certain methoxylated compounds may have toxic effects on microbial communities. DNA analysis of microbial communities from the incubations are ongoing and follow up experiments are being designed with 13C-labeled substrates to better distinguish methane production as result of MAC methanogenesis from other potential pathways. When complete these investigations should provide valuable insights the prevalence and mechanisms for MAC based methanogenesis in peatland ecosystems.