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Microbial Ecology in Reservoirs and Lakes

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Front. Microbiol. | doi: 10.3389/fmicb.2019.01229

The DNRA-denitrification dichotomy differentiates nitrogen transformation pathways in mountain lake benthic habitats

  • 1Centro de Investigación Ecológica y Aplicaciones Forestales (CREAF), Spain
  • 2Centro de Estudios Avanzados de Blanes (CEAB), Spain
  • 3Department of Forest Mycology and Plant Pathology, Faculty of Forest Sciences, Swedish University of Agricultural Sciences, Sweden
  • 4Spanish National Research Council (CSIC), Spain

Effects of nitrogen (N) deposition on microbially-driven processes in oligotrophic freshwater ecosystems are poorly understood. We quantified guilds in the main N-transformation pathways in benthic habitats of 11 mountain lakes along a dissolved inorganic nitrogen gradient. The genes involved in denitrification (nirS, nirK, nosZ), nitrification (archaeal and bacterial amoA), dissimilatory nitrate reduction to ammonium (DNRA, nrfA) and anaerobic ammonium oxidation (anammox, hdh) were quantified, and the bacterial 16S rRNA gene was sequenced. The dominant pathways and associated bacterial communities defined four main N-transforming clusters that differed across habitat types. DNRA dominated in the sediments, except in the upper layers of more productive lakes where nirS denitrifiers prevailed with potential N2O release. Loss as N2 was more likely in lithic biofilms, as indicated by the higher hdh and nosZ abundances. Archaeal ammonia oxidisers predominated in the isoetid rhizosphere and rocky littoral sediments, suggesting nitrifying hotspots. Overall, we observed a change in potential for reactive N recycling via DNRA to N losses via denitrification as lake productivity increases in oligotrophic mountain lakes. Thus, N deposition results in a shift in genetic potential from an internal N accumulation to an atmospheric release in the respective lake systems, with increased risk for N2O emissions from productive lakes.

Keywords: Denitrificafion, DNRA, lithic biofilms, Mountain lake, nitrogen deposition, Remote ecosystems, sediment, 16S

Received: 15 Jan 2019; Accepted: 16 May 2019.

Edited by:

Haihan Zhang, Xi'an University of Architecture and Technology, China

Reviewed by:

Katharina Kujala, University of Oulu, Finland
Marja Tiirola, University of Jyväskylä, Finland  

Copyright: © 2019 Palacin-Lizarbe, Camarero, Hallin, Jones, Caliz, Casamayor and Catalan. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Ms. Carlos Palacin-Lizarbe, Centro de Investigación Ecológica y Aplicaciones Forestales (CREAF), Barcelona, Spain, cpalacli7@gmail.com