ABSTRACTAnaerobic ammonium oxidation with nitrite reduction to dinitrogen (termed anammox) has been reported to be an important process for removing fixed nitrogen (N) in marine ecosystems and in some agricultural and wetland soils. However, its importance in upland forest soils has never been quantified. In this study, we evaluated the occurrence of anammox activity in two temperate forest soils collected from northeastern China. With15N-labeled NO3−incubation, we found that the combined potential of the N2production rates of anammox and codenitrification ranged from 0.01 ± 0.01 to 1.2 ± 0.18 nmol N per gram of soil per hour, contributing 0.5% to 14.4% of the total N2production along the soil profile. Denitrification was the main pathway of N2production and accounted for 85.6% to 99.5% of the total N2production. Further labeling experiments with15NH4+and15NO2−indicated that codenitrification was present in the mixed forest soil. Codenitrification and anammox accounted for 2% to 12% and 1% to 7% of the total N2production, respectively. Two anammox species, “CandidatusBrocadia fulgida” and “CandidatusJettenia asiatica,” were detected in this study but in very low abundance (as indicated by thehzsBgene). Our results demonstrated that the anammox process occurs in forest soils, but the contribution to N2loss might be low in these ecosystems. More research is necessary to determine the activities of different N2releasing pathways in different forest soils.IMPORTANCEIn this study, we examined the anammox activity in temperate upland forest soils using the15N isotope technique. We found that the anammox process contributed little to the N2production rate in the studied forest soil. Two anammox organisms, “CandidatusBrocadia fulgida” and “CandidatusJettenia asiatica,” were detected. In addition, we found that codenitrification was another N2production pathway in forest soils. Our results could contribute to the understanding of soil gaseous N losses and microbial controls in forest soils.
Long-term forest soil warming alters microbial communities in temperate forest soils
