PARENT SESSION
Contributed Oral Session 125: Soil Ecology: Carbon - Nitrogen Cycling
Thursday, August 11, 8:00 AM - 11:30 AM, Meeting Room 524 B, Level 5, Palais des congrès de Montréal
Charcoal from forest fire influences ammonium oxidizing bacteria and nitrogen cycling.
MacKenzie, M.Derek*,1, Ball, Patrick2, Pollock, Jarrod2, Holben, William 2, DeLuca, Thomas1, 1 Department of Ecosystem and Conservation Sciences, Missoula, MT, USA2 Microbrobial Ecology Program, Missoula, MT, USA
ABSTRACT- Forest fires create copious amounts of charcoal that persists at the soil/forest floor interface for hundreds of years, but few studies have focused on the potential of charcoal to influence long-term nitrogen (N) cycling and microbial communities, specifically ammonia oxidizing bacteria (AOB). Fire has been shown to increase N mineralization immediately, but we believe that the deposition of charcoal maintains elevated N availability for up to 40 years in ponderosa pine forests of the inland Northwest and for up to 80 years in Boreal forests. Previous work has shown that both nitrate concentration and potential nitrification decrease with fire exclusion. We found gross and net nitrification to be higher in the presence of charcoal using isotope pool dilution methods, indicating that charcoal is affecting nitrification rates and not just changing immobilization rates. We are also examining the AOB community using most probable number (MPN) and the polymerase chain reaction (PCR), using primer sets specific for the ammonia monooxygenase gene (amoA) or 16S rDNA of AOB. To examine the AOB community structure, denaturing gradient gel electrophoresis (DGGE) is being utilized and abundance is being examined by quantitative PCR (q-PCR). Preliminary evidence suggests that presence of charcoal may affect AOB abundance and community structure in ponderosa pine ecosystems. Further, an observed decrease in nitrification along a fire chronosequence may suggest a parallel decrease in AOB numbers and changes in community structure, indicating a lack of substrate possibly as the result of charcoal mediated humification rates.
Key words: Microbial Ecology, Biogeochemistry, Forest Soil, Fire Exclusion