HR: 1400h
AN: B13A-06    [Abstracts]
TI: Investigating the Relative Importance of Nitrification and Denitrification in Generating Nitrous Oxide Emissions From N-amended Soils of a Managed Northern Temperate Forest Chronosequence Using δ¹⁵N and δ¹⁸O
AU: * Kumar, S
EM: sanjeev_research@yahoo.com
AF: Environmental Sciences Research Centre, St. Francis Xavier University, Antigonish, NS B2G 2W5, Canada
AU: Kellman, L
EM: lkellman@stfx.ca
AF: Environmental Sciences Research Centre, St. Francis Xavier University, Antigonish, NS B2G 2W5, Canada
AB: Nitrous oxide (N₂O) is emitted from forest soils, however, our understanding of the processes controlling these emissions is insufficient to narrow down current flux estimates in northern temperate forests. Here, we investigate the relative importance of nitrification and denitrification in generating potential N₂O emissions in a managed orthic hummo-ferric podzol forest soil of Nova Scotia, Canada using nitrogen amendments, natural δ¹⁵N and δ¹⁸O in N₂O and a controlled laboratory incubation approach. Shallow soil samples were collected at sites characterized by similar soil type, topography, and climate, and represented 125 ± yr old growth along with previously harvested 80 yr, 45 yr, 15 yr forests, and a recently clear-cut (3 month) forest soil. Experimental conditions subjected soil samples along this age sequence of harvested red spruce forests to conditions favorable for either nitrification or denitrification. The temporal change in N₂O concentration and δ¹⁵N and δ¹⁸O of emitted N₂O was monitored in order to investigate N₂O emission patterns and how the isotopic composition of N₂O changed through time. A linear increase in N₂O concentration with time was observed in the headspace of sample bottles under conditions favourable for denitrification, whereas no significant change in N₂O concentrations, with the exception of the recent 3-month old clear-cut, was observed in samples under conditions favourable for nitrification. In general, the δ¹⁵N and δ¹⁸O of emitted N₂O during denitrification conditions were around -40 and 15 ‰, respectively, an isotopic signature of denitrification. The δ¹⁵N and δ¹⁸O during nitrification favorable conditions were 10 and 30 ‰, respectively, except at the 3-month old clear-cut where it was -40 and 10 ‰, respectively. The depleted isotopic signature and higher N₂O emissions from the recently clear-cut soils demonstrates the importance of denitrification as a N₂O source even under conditions favoring nitrification.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0469 Nitrogen cycling
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: 2009 Joint Assembly