Nitrous oxide dynamics in managed northern forest soil profiles: is production offset by consumption?

Abstract

This study investigates soil N2O dynamics in forest soils representing early (3-years) and late (>50 years) post-harvest succession in Atlantic Canada over a 9-month snow-free period in order to develop a better understanding of the role of managed forests as sources and sinks of N2O. We couple measurement of surface flux with detailed measurements of subsurface N2O concentrations at four mineral soil depths (0, 5, 20 and 35 cm) at 40 plots located within four sites. Median surface fluxes were similar at all sites regardless of the management stage (−5 to +19 ugN2O–N/m2/day), with all sites behaving as net sinks and sources of N2O over the measurement period. Subsurface mineral soil N2O concentrations at early (3-year) post-harvest succession sites, which ranged from median values of 362 ppbv at 0 cm to 1783 ppbv at 35 cm depth, were significantly higher than late post-harvest succession sites where median concentrations ranged from 329 ppbv at 0 cm to 460 ppbv at 35 cm depth. Examination of relationships between subsurface gas storage and surface flux magnitudes, suggested although recently harvested forest soils may be producing N2O at a greater rate than mature forest soils, observed patterns are consistent with a strong sink for this gas that prevents its conservative transport through the soil profile, and ultimate emission to the atmosphere through the majority of the measurement period.