Nitrification controls N2O production rates in a frozen boreal forest soil

The winter season has been identified as a significant contributor to N2O emissions from boreal soils, but our understanding of the processes regulating these emissions is fragmentary. We investigated potential N-sources and pathways involved in N2O formation in a frozen boreal forest soil by labeling soil samples with N-15-containing substrates, and measured rates of (N2O)-N-15/N-15(2) formation under both oxic and anoxic conditions. Our results showed that all N2O produced in the frozen samples originate from denitrification, but the rate-limiting factor is NO3- availability, which is largely governed by nitrification. This suggests that N2O formation in frozen boreal soils may be sustained for a prolonged period of time, but is governed by a delicate balance of the O-2 regime. (c) 2007 Elsevier Ltd. All rights reserved.