Microbial Biogeochemistry Under Enhanced Nutrient Deposition In a Northern Bog.

Microorganisms are vital in the role northern peatlands play as long-term sinks for atmospheric carbon dioxide, due to slow rates of decomposition, and as sources of atmospheric methane, through the net activity of methanogenic archaea and methane-oxidizing bacteria. Enhanced nutrient, primarily nitrogen (N), deposition, has the potential to disrupt microbial dynamics in peatlands and therefore alter the roles these ecosystems play in global climate.  This presentation reports a series of research projects conducted at the Mer Bleue bog (near Ottawa Canada) in the longest known simulated atmospheric nutrient deposition experiment that began in 2000. Activities of microbial communities have been characterized using laboratory incubations and field greenhouse gas fluxes measured using chamber techniques.  Microbial diversity has been characterized after 7 years of elevated N, or N with phosphorus (P) and potassium (K) using molecular genetic fingerprinting and phylogenetic analysis of signature genes in fungi, bacteria, methanogens, and methane oxidizing bacteria, and earlier using phospholipids fatty acid analyses.  Controls on microbial activities of specific populations have been studied with selective inhibitors and organic substrate additions.  Most recent work indicates that high rates (10 times above ambient annual deposition) of simulated N deposition as ammonium nitrate with P and K decreased fungal respiration relative to prokaryote respiration, decreased methane production, and enhanced methane oxidation measured in the laboratory, however patterns of field flux rates across treatments were less clear.  In general, changes in microbial diversity or activity across increasing levels of N (with a fixed level of additional P and K) appear to be mediated indirectly by changes in the plant community, with for example, reduced C substrate delivery to methanogens from roots near the water table in the soil profile and reduced occurrence of molecular detection of purported mycorrhizal fungi and total fungal respiration.