Greenhouse gas metabolizing prokaryotes in peatlands

Peatlands in the northern hemisphere store substantial amounts of carbon and nitrogen, and are predicted to react sensitively to global warming. The main objective of the study was to study microbial processes involved in the fluxes of the greenhouse gases methane (CH4) and nitrous oxide (N2O) from peatlands. Five model peatlands with contrasting features (e.g., nitrate content, mean annual temperature, pH) were assessed. A pH-neutral fen produced CH4 in situ as well as in unsupplemented anoxic microcosms. Supplemental N-Acetylglucosaminestimulated formation of fermentation products and CH4 and lead to increased accumulation of fermentation products when methanogenesis was inhibited by Bromoethanesulfonate. Supplemental H2/CO2 and formate greatly stimulated methanogenesis, while acetate and methanol stimulated methanogenesis to a much lesser extent. A high family-level diversity of bacterial 16S rRNA genes was detected. Within the detected families, genera known for syntrophic interactions with methanogens were found. Diversity of methanogens was lower than bacterial diversity, as only hydrogenotrophic Methanomicrobiales and Methanocellales were detected. Both process data and molecular data suggest that (i) hydrogenotrophic methanogenesis is the main process of CH4 formation in pH-neutral fen soil, and (ii) a high diversity of bacterial families are likely involved in diverse fermentations, providing substrates for methanogens. Denitrification and N2O consumption potentials as well as denitrifier community composition were assessed in all five northern peatlands. In situ N2O emissions range from < 0.01 to 10 mg N2O*m-2*d-1,and were positively and negatively correlated with soil nitrate and ammonia contents, respectively. All soils produced and consumed N2O in anoxic microcosms without apparent delay. N2O production capacities and apparent affinities for nitrate were likewise positively correlated with soil nitrate content. Phylogenetic analyses of the nitrate reduction- and denitrification-associated genes narG, nirK/nirS, and nosZ indicated that the diversity of the denitifier community was highest in pH-neutral fen soil and positively correlated with pH. Detected narG affiliated mainly with Betaproteobacterial and Actinobacterial narG. . The number and the identity of observed operational taxonomic units (OTUs) of nirK, nirS, and nosZ in pH-neutral fen soil was clearly distinct from those of the more acidic soils, and indicated Alpha-, Beta-, and Gammaproteobacterial denitrifiers in all peatlands. Permafrost-affected soils mainly clustered together in the canonical correspondence analysis plots of the analyzed genes. pH was the most important factor determining community composition of nitrate reducers and denitrifiers.Significant influences of soil carbon content, precipitation, or temperature were also detected. The occurrence of certain OTUs of nirK and nirS was positively correlated with N2O emissions. The collective data indicate that (i) denitrification is an ongoing process in different types of pristine peatland soils, (ii) source and sink function of peatland denitrifiers for N2O are influenced by soil nitrate content and denitrifier community composition, and (iii) nitrate reducer and denitrifier community composition are affected by pH, temperature, precipitation, and soil carbon content. Global warming is predicted to increase the frequency of extreme weather events, affecting on the water table level in peatlands and on the microbial communities involved in the production of CH4 and N2O. Thus, the influence of short-term water table manipulations including application of artificial drought conditions or excessive flooding was assessed in the acidicfen. Fermentative, methanogenic and denitrifying potentials in anoxic microcosm studies revealed that the potential activity of methanogens and denitrifiers was affected by changing water tables, whereas the potential activity of fermenters was largely unaffected. Changes in the copy numbers of mcrA, narG, and nosZ detected by quantitative PCR were rather small when compared to the observed changes in potential activity. Community composition of methanogens, nitrate and N2O-reducers was similar at all sampled timepoints of the manipulation experiments. The collective data indicate a stable microbial community in fen soil that is able to adapt its activity to the changing conditions quite rapidly.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2012

Author dc:creator

• Palmer, Katharina

Contributors dc:contributor

• Horn, Marcus

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/174/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:174