N2O flux in alas ecosystems formed by forest disturbance near Yakutsk, Eastern Siberia, Russia

An alas is a round area of grassland with a pond at the center, formed by subsidence associated with permafrost thawing in taiga forests in eastern Siberia. To characterize the relationship between the N2O dynamics and soil properties of forest-alas ecosystems, we investigated soil N2O fluxes in four thermokarst ecosystems composed of forest, grassland, and ponds near Yakutsk in July 2000. At all sites, pH, EC, and organic carbon (OC) content in soil were higher in the grasslands (pH 7.3-9.3, EC 22-63 mS/m, OC 1.4%-15.3%) than in the forests (5.6-6.3, 1.4-6.8 mS/m, 0.4%-1.7%), and C/N was lower in the grasslands (10-18) than in the forests (18-24). Both emission (positive values) and uptake (negative values) of N2O occurred in the forests (-2.1 to 1.0 microg N/square m/h) and grasslands (-1.3 to 31 microg N/square m/h). N2O emissions at the edge of ponds varied widely (0 to 140 microg N/square m/h). N2O was taken up in the ponds (-2.2 to 0.0 microg N/square m/h). There were significant differences in N2O fluxes among land cover types. N2O flux was positively correlated with soil moisture, but N2O fluxes were smallest in the ponds because of the biological denitrification there. Therefore, an increase in soil moisture increased N2O flux.