Nitrous Oxide Consumption Potentials of Well-drained Forest Soils in Southern Québec, Canada

Abstract

To establish the major controls on N ₂ O consumption by forest soils, we conducted laboratory incubations of 16 samples from four soil types, two organic and two mineral, varying in overlying forest vegetation (sugar maple, American beech and eastern hemlock). The fastest potential consumption of N ₂ O occurred under anoxic conditions with little soil nitrate and under elevated headspace N ₂ O concentration. Potential N ₂ O consumption rates were fastest in organic soils under hemlock and beech trees (111 and 75 ng N ₂ O-N g ⁻¹ d ⁻¹ , respectively) compared to mineral soils under beech and maple trees (45 and 41 ng N ₂ O-N g ⁻¹ d ⁻¹ ). Organic soils showed faster N ₂ O consumption rates than mineral soils, possibly due to larger organic C levels and higher C:N ratios. Acetylene treatment confirmed that denitrification was the process underlying N ₂ O consumption. These results suggest that soils regularly consume N ₂ O with varying magnitude, most likely in anoxic microsites throughout the soil profile and that the potential for N ₂ O consumption is larger in organic than in mineral forest soils.

Keywords:

• denitrification
• forest soils
• nitrification
• N cycling
• N₂O consumption
• N₂O fluxes
• N₂O production

Many thanks to Mike Dalva and Hélène Lalande for laboratory assistance and to Dr. M. Lechowicz and Benoît Hamel at Gault Nature Reserve, Mont St. Hilaire and Dr. J. Fyles and Christina Izdiak at Morgan Arboretum for access to forest sites. The research was supported by grants from the Canadian Foundation for Climate and Atmospheric Sciences, the Natural Sciences and Engineering Research Council of Canada and the Faculty of Science, McGill University.

Notes

∗C:N ratio in soils under beech trees represent an average of both organic and mineral layer as only a 0-10 cm depth sample was taken for this purpose.

∗∗ Represents total litter N input on the soil surface and its C:N ratio.