Soil Fluxes of Carbon Dioxide, Nitrous Oxide, and Methane at a Productive Temperate Deciduous Forest

Abstract

We measured CO₂, N₂O, and CH₄ fluxes between soils and the atmosphere in ambient and N‐addition plots at a productive black cherry‐sugar maple forest in northwest Pennsylvania to examine the link between N‐cycling and trace gas fluxes. Fluxes were estimated the using in‐situ chambers. Net annual N mineralization was 121.0 kg N ha⁻¹yr⁻¹, and net nitrification was 85.8 kg N ha⁻¹ yr⁻¹, or 71% of net mineralization. Carbon dioxide (5.09 Mg C ha⁻¹ yr⁻¹) efflux and CH₄ uptake (8.90 kg C ha⁻¹ yr⁻¹) were among the highest rates reported for temperate deciduous forests. Emissions of N₂O (0.228 kg N ha⁻¹ yr⁻¹) were within the range of rates reported elsewhere, including locations with lower rates of N‐cycling. A short‐term study (May–Oct.) showed that N fertilization reduced both CO₂ emissions and CH₄ uptake (CO₂ by 19%; CH₄ by 24%). N₂O effluxes in fertilized plots were not different from control plots. The relatively high rate of soil respiration corresponded to a high rate of N‐cycling; however, N₂O emissions were not substantially greater than those measured at other locations, suggesting that rapid N‐cycling or N additions in temperate forests do not necessarily result in large emissions of N₂O. Concurrent rapid rates of N‐cycling and high rates of CH₄ uptake did not support the hypothesis that N‐cycling rates directly control CH₄ uptake. Links between N‐cycling and CH₄ oxidation are complex; the influence of N‐cycling on flux rates must consider not only the rate of cycling, but also the disposition of N‐cycling products, and the factors that influence rates of N dynamics.