Spatial Variations of Soil N 2 and N 2 O Emissions from a Temperate Forest: Quantified by the In Situ 15 N Labeling Method.

Emissions of dinitrogen (N₂) and nitrous oxide (N₂O) from soil are important components of the global nitrogen cycle. Soil N₂O emissions from terrestrial ecosystems have been well studied. However, patterns and mechanisms of N₂ emissions remain unclear due to the technical difficulty in measuring N₂ production. In this study, an in situ ¹⁵N labeling method was employed to determine soil N₂ and N₂O emission rates from the lower, middle, and upper slopes, which correspond to different moisture conditions, in a temperate forest in Northeast China. We found that N₂ emissions varied from 85 to 3442 μg N m⁻² h⁻¹ across the slopes and were dominated by denitrification. The emissions of bulk N₂O (22 to 258 μg N m⁻² h⁻¹) and denitrification-derived N₂O (14 to 246 μg N m⁻² h⁻¹) were significantly lower than N₂ emissions from their corresponding slope positions. Both N₂ and N₂O emissions significantly increased when soils become wetter. The ratios of N₂O/(N₂O + N₂) were significantly higher at the upper and middle slopes (0.22 and 0.20, respectively) compared with those at the lower slope (0.08 ± 0.01). At the catchment scale, N₂ accounted for 85% of the total gaseous N losses (N₂O + N₂). Our study shows that soil moisture drives the patterns of N₂ and N₂O emissions and field quantification of N₂O/(N₂O + N₂) ratio should further consider the effect of slope position of forest ecosystems to estimate total soil gaseous N losses. [ABSTRACT FROM AUTHOR]