Anammox Process Exists, but Contributes Little to Soil N2 Production in Two Temperate Forests

Release Time:2016-07-20 Big Small

Denitrification (in which nitrate is reduced to N2 by multiple steps) had been considered as the only pathway for nitrogen (N) removal in the form of dinitrogen (N2) and is an important mechanism for explaining the N limitation in both terrestrial and aquatic ecosystems. However, the discovery of anaerobic ammonium oxidation (anammox, under anaerobic conditions, ammonium is oxidized by nitrate to N2) in various natural and artificial habitats since 1995 has changed the understanding of traditional N biogeochemical cycle. The anammox process has been reported as an important N2 production process in aquatic ecosystems, and some agricultural and wetland systems. Forest soils may be favorable to the development of anammox bacteria and the occurrence of anammox due to both the nature of co-existing ammonium and nitrate and the presence of oxic/anoxic interfaces. Up to date, however, there is only one study that detected the presence of the anammox bacteria in a riparian forest wetland soil, and the potential quantitative significance of anammox in forest soils has not yet been reported.

Stable Isotope Ecology Group of Institute of Applied Ecology, Chinese Academy of Sciences led by Fang Yunting, set up a new 15N2 gas on-line analysis system and used the 15N labeling and pairing technique to evaluate anammox activity in soils from two temperate forest (a mixed broad-leaved forest and a larch forest) in northeastern China. They found that the anammox process indeed occurred in forest soils, but with low production rates (0.06 to 0.08 nmol N g-1 h-1) which only contributed 1% to 7% of the total N2 production. Two anammox genera, Candidatus Brocadia fulgida and Candidatus Jettenia asiatica, were detected in this study, but in very low abundance (as indicated by the hzsB gene). In addition, the results from 15NH4+ and 15NO2- labeling experiments further indicated that co-denitrification (a microbially mediated process by which one N atom of nitrite or nitric oxide combines with one N atom of another N species, e.g., amino compound, to form N2O and/or N2) was present in forest soil and accounted for 2% to12% of the total N2 production.

This paper titled by Contribution of Anammox to Nitrogen Removal in Two Temperate Forest Soils was published by the journal of Applied and Environmental Microbiology (2016,82(15):4602-4612.doi:10.1128/AEM.00888-16;http://aem.asm.org/content/82/15/4602). This work was financially supported by the National Natural Science Foundation of China (Nos. 31422009 and 31370464), the Hundred Talents Program of the Chinese Academy of Sciences (No. Y1SRC111J6), and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB15020200).

 Full text URL: http://aem.asm.org/content/82/15/4602

Abstract: Anaerobic 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. With 15N-labeled NO3 incubation, we found that the combined potential of the N2 production 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 N2 production along the soil profile. Denitrification was the main pathway of N2 production and accounted for 85.6% to 99.5% of the total N2 production. Further labeling experiments with15NH4+ and 15NO2 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 N2 production, respectively. Two anammox species, “CandidatusBrocadia fulgida” and “Candidatus Jettenia asiatica,” were detected in this study but in very low abundance (as indicated by the hzsB gene). Our results demonstrated that the anammox process occurs in forest soils, but the contribution to N2 loss might be low in these ecosystems. More research is necessary to determine the activities of different N2 releasing pathways in different forest soils.

Importance :In this study, we examined the anammox activity in temperate upland forest soils using the 15N isotope technique. We found that the anammox process contributed little to the N2 production rate in the studied forest soil. Two anammox organisms, “Candidatus Brocadia fulgida” and “Candidatus Jettenia asiatica,” were detected. In addition, we found that codenitrification was another N2 production pathway in forest soils. Our results could contribute to the understanding of soil gaseous N losses and microbial controls in forest soils.

Publication Name: Dan Xi, Ren Bai, Limei Zhang, Yunting Fang.

Email: fangyt@iae.ac.cn.