Abstract of PhD Thesis

The microbial ecology of Irish Atlantic blanket peatlands

Olivia Rice (2007), National University of Ireland, Galway

Vegetative heterogeneity and microtopographical variation have important consequences for carbon fluxes in Sphagnum-based Atlantic blanket bogs and, to obtain a better understanding of the biogeochemical processes occurring in, and the ecological complexities presented by, these anoxic soils, research into the identity and abundance of the microbial communities present must be undertaken. One key knowledge gap is the absence of qualitative data to describe the microbial community structure associated with particular topographical and ecohydrological features in bogs. The aims of this thesis were firstly, to determine a method to extract microbial DNA from peat, which would give a representative impression of the microbial community, when the bogs were analysed by polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) profiling. Second, 16S rRNA-based DGGE profiles were generated for the bacterial and archaeal communities associated with: (1) hydrologically defined topographical features (microsites; Hummock, High Lawn and Low Lawn) in a pristine Atlantic peat bog; (2) ecohydrologically similar, but spatially disparate microsites and (3) similarly classified, but geographically separate peat bogs. Relationships between microbial community structure and the physical factors, which affect the microsite characteristics, were then inferred. The results obtained suggested that:

  • The bacterial community of the blanket bogs was mainly composed of γ-Proteobacteria, Clostridia, Actinobacteria and Chlorobi, while the archaeal community was composed of hydrogenotrophic methanogens (Methanomicrobiales) and Crenarchaeota;
  • The bacterial community profiles were strongly and reproducibly, influenced by the physical and chemical characteristics of particular microsites;
  • The bacterial communities across spatially diverse, but hydrologically and ecologically defined microsites, were very similar;
  • The spatial relationship between diverse microsites and community structure was not well defined for Archaea;
  • Distinct bacterial and archaeal community structure profiles developed in the two geographically separate Atlantic blanket bogs sites, but physiologically similar methanogenic communities, and phylogenetically similar bacterial communities, were present in both sites;
  • Alteration of the water table in a blanket bog influenced the microbial community structure profiles. Specifically, a reduction in the relative diversity of methanogens in the drained sites, which was also reflected in the net flux of methane, was noted.