Mots-clé
(Anglais)
|
nitrogen cycling; rhizosphere; soil; denitrification; anammox
|
Programme de recherche
(Anglais)
|
COST-Action 856 - Ecological aspects of denitrification with emphasis on agriculture
|
Description succincte
(Anglais)
|
In this project we wish to investigate a so far neglected process in the terrestrial N-cycle: the anaerobic oxidation of ammonium ('anammox'), which has been shown in marine environments to contribute significantly to dinitrogen formation. We hypothesize that anoxic pockets in soil aggregates and the rhizosphere of plants represent suitable microenvironments where the anammox process may be active. With an interdisciplinary approach, combining methods from biogeochemistry and molecular microbial ecology, we aim at detecting and quantifying anammox in terrestrial environments. PCR based techniques will be applied for screening and identification of anammox bacteria in a wide range of habitats. The relative contribution of anammox and denitrification to N2 formation and the factors controlling the two processes and their interactions will be explored in microcosm experiments with 15N additions. The expected results will improve our understanding of N2 producing processes in soils and lead to a more complete picture of the terrestrial N-cycle.
|
Partenaires et organisations internationales
(Anglais)
|
AT, BE, CH, CZ, DE, DK, ES, FI, FR, GR, HU, IE, IT, NL, NO, PL, SE, SI, SK, UK
|
Résumé des résultats (Abstract)
(Anglais)
|
The importance of anammox (anaerobic ammonium oxidation) in nitrogen cycling has been widely studied in aquatic environments, including chemoclines of stratified water columns and surface sediments. However, nothing was known about the distribution, diversity, and activity of anammox bacteria in terrestrial ecosystems. In the course of this project we provided molecular evidence for the presence of anammox bacteria in a wide range of soil types. Phylogenetic analysis of environmental 16S rRNA gene sequences showed that anammox bacteria affiliated Candidatus 'Brocadia', 'Kuenenia', Scalindua', Anammoxoglobus', 'Jettenia', and two unidentified but related clusters are present in soils. This means that all of the candidate genera described so far from wastewater treatment systems were also detected in soils. As in aquatic systems anammox is essentially conducted by Ca. Scalindua, this suggests a higher diversity of anammox bacteria in soils. Moreover, anammox bacteria were neither present in every sampled environment nor soil fraction, which demonstrates their heterogeneous distribution and ecological requirements. Anammox bacteria were principally detected at oxic/anoxic interfaces, provided that inorganic nitrogen compounds were available. Despite the apparent diversity of anammox bacteria in soils they seem to be only of low abundance as indicated by the requirement for a nested PCR approach for their detection and very low cell counts by FISH. Soil incubation experiments with 15N isotope labeling permitted nevertheless detection of anammox activity. The production of 29N2 was observed at different depth along the soil profile demonstrating the activity of anammox bacteria. During the year, the activity varied between seasons and depths and was lowest (i.e. not detectable) during the vegetational period probably due to the competition with plants for combined nitrogen. In agreement with the molecular results, the amount of N2 produced by anammox is low, representing only about 1-2% of the total N2 production. This represents the first study providing evidence for the presence and activity of anammox bacteria in terrestrial ecosystems.
|
Références bases de données
(Anglais)
|
Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. +41 31 322 74 82 Swiss Project-Number: C04.0269
|
