Gross nitrogen transformations in harvested and mature aspen-conifer mixed forest soils from the Boreal Plain

Harvesting of aspen-conifer mixed forests on the Boreal Plain of western Canada is increasing with growing demands for the regionʹs natural resources. To determine the effects upon soil N we measured net and gross N transformations in harvested and mature aspen-conifer mixed forest soils using the 15N isotope dilution technique. Gross ammonification ranged from 81 to 165 μg NH4-N g−1 d−1, and rates were consistently higher for harvested soils. Rates of gross ammonification were similar to gross NH4 immobilization and concurred with low net ammonification rates in both the mature and harvested soils. Gross and net NO3 transformations were near detection limits in both the mature and harvested soils, however, the latter soils had elevated NO3 concentrations, which suggest gross nitrification in excess of immobilization occurs at times.