| The pristine peatlands of Alberta, Canada are currently experiencing an increase in atmospheric nitrogen (N) deposition coupled with a rise in the intensity and frequency of wildfires. Given the global importance of peatlands as a large net carbon (C) sink relative to their land area, understanding nutrient cycling dynamics and the effect of these disturbances is paramount. Obtaining accurate rates of N mineralization and nitrification can augment our current understanding of N-limitation, plant-microbe competition, and nutrient availability in bogs. Net N mineralization was quantified (buried bag technique) in the summers of 2013, 2014, and 2015 along a chronosequence of five bog sites that represent 2 to 113 years since fire (YSF) in 2013. Each site contains six replicate plots of four different N treatments: control, 0, 10, and 20 kg N ha-1 yr-1. Significant differences in rates of net ammonification and nitrification were observed in site and round of measurement, but not in N treatment. Net DIN production was higher at older sites (net ammonification added to net nitrification, averaged across year, sampling round, and treatment in mug N m-2 d-1, was 933, 736, 137, 723, and 140 at 113, 73, 32, 12, and 2 YSF, respectively), which is counter to the hypothesis that available N, and thus net N mineralization, would be higher in recently burned bogs due to the slower recovery rate of mycorrhizal vegetation and lower C:N ratios due to labile C release from roots post-fire. Measurement of gross N ammonification, nitrification, and microbial N consumption rates could indicate whether the low net N mineralization rates reported for these bog sites are associated with slow or rapid turnover of the dissolved inorganic N pool. |
