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

Abstract

AbstractWe 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.