Net nitrogen mineralization in Alberta bog peat is insensitive to experimentally increased nitrogen deposition and time since wildfire

Across northern Alberta, Canada, bogs experience periodic wildfire and, in the Fort McMurray region, are exposed to increasing atmospheric N deposition related to oil sands development. As the fire return interval shortens and/or growing season temperatures increase, the regional peatland CO2-C sink across northern Alberta will likely decrease, but the magnitude of the decrease could be diminished if increasing atmospheric N deposition alters N cycling in a way that stimulates post-fire successional development in bogs. We quantified net ammonification, nitrification, and dissolved organic N (DON) production in surface peat along a post-fire chronosequence of five bogs where we also experimentally manipulated N deposition (no water controls plus 0, 10, and 20 kg N ha(-1) yr(-1) simulated deposition, as NH4NO3). Initial KCl-extractable NH4+-N, NO3--N and DON averaged 176 +/- 6, 54 +/- 0.2, and 3580 +/- 40 ng N cm(-3), respectively, with no consistent changes as a function of time since fire and no consistent effects of experimental N addition. Net ammonification, nitrification, and DON production averaged 3.8 +/- 0.3, 1.6 +/- 0.2, and 14.3 +/- 2.0 ng N cm(-3) d(-1), also with no consistent changes as a function of time since fire and no consistent effects of experimental N addition. Our hypothesis that N mineralization would be stimulated after fire because root death would create a pulse of labile soil organic C was not supported, most likely because ericaceous plant roots typically are not killed in boreal bog wildfires. The absence of any N mineralization response to experimental N addition is most likely a result of rapid immobilization of added NH4+-N and NO3 (-)-N in peat with a wide C:N ratio. In these boreal bogs, belowground N cycling is likely characterized by large DON pools that turn over relatively slowly and small DIN pools that turn over relatively rapidly. For Alberta bogs that have persisted at historically low N deposition values and begin to receive higher N deposition related to anthropogenic activities, peat N mineralization processes may be largely unaffected until the peat C:N ratio reaches a point that no longer favors immobilization of NH4+-N and NO3--N.