title: Nitrogen loss by anaerobic ammonium oxidation in unconfined aquifer soils.
abstract: Anaerobic ammonium oxidation (anammox) is recognized as an important process for nitrogen cycling, yet little is known about its role in the subsurface biosphere. In this study, we investigated the presence, abundance, and role of anammox bacteria in upland soil cores from Tianjin, China (20 m depth) and Basel, Switzerland (10 m depth), using isotope-tracing techniques, (q)PCR assays, and 16 S rRNA &hzsB gene clone libraries, along with nutrient profiles of soil core samples. Anammox in the phreatic (water-saturated) zone contributed to 37.5-67.6% of the N-loss (up to 0.675 gN m-2d-1), with anammox activities of 0.005-0.74 nmolN g-1soil h-1, which were even higher than the denitrification rates. By contrast, no significant anammox was measured in the vadose zone. Higher anammox bacterial cell densities were observed (0.75-1.4 × 107copies g-1soil) in the phreatic zone, where ammonia-oxidizing bacteria (AOB) maybe the major source of nitrite for anammox bacteria. The anammox bacterial cells in soils of the vadose zone were all <103copies g-1soil. We suggest that the subsurface provides a favorable niche for anammox bacteria whose contribution to N cycling and groundwater nitrate removal seems considerably larger than previously known.
authors.affiliation: Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China.
authors.forename: Shanyun
authors.initials: S
authors.lastname: Wang
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dubendorf, Switzerland.
authors.forename: Dirk
authors.initials: D
authors.lastname: Radny
authors.affiliation: Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences, Shijiazhuang 050061, China.
authors.forename: Shuangbing
authors.initials: S
authors.lastname: Huang
authors.affiliation: Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China.
authors.forename: Linjie
authors.initials: L
authors.lastname: Zhuang
authors.affiliation: Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China.
authors.forename: Siyan
authors.initials: S
authors.lastname: Zhao
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dubendorf, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Berg
authors.affiliation: Department of Microbiology, Radboud University, Nijmegen, Netherlands.
authors.forename: Mike S M
authors.initials: MS
authors.lastname: Jetten
authors.affiliation: Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China.|Department of Biogeochemistry, Max Planck Institute for Marine Microbiology, Bremen, Germany.
authors.forename: Guibing
authors.initials: G
authors.lastname: Zhu