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Applied and Environmental Microbiology, August 2009, p. 4993-5000, Vol. 75, No. 15
0099-2240/09/$08.00+0 doi:10.1128/AEM.02917-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Quantification of Key Genes Steering the Microbial Nitrogen Cycle in the Rhizosphere of Sorghum Cultivars in Tropical Agroecosystems 
Brigitte Hai,1*
Ndeye Hélène Diallo,2
Saidou Sall,2
Felix Haesler,3
Kristina Schauss,1
Moussa Bonzi,4
Komi Assigbetse,2
Jean-Luc Chotte,5
Jean Charles Munch,3 and
Michael Schloter1
Helmholtz Zentrum München, German Research Center for Environmental Health, Department of Terrestrial Ecogenetics, Institute of Soil Ecology, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany,1
Centre de Recherche IRD-ISRA de Bel Air, Laboratoire d'Ecologie Microbienne des Sols et Agrosystèmes Tropicaux, Route des Hydrocarbures, BP 1386, CP 18524 Dakar, Sénégal,2
Technical University Munich, Chair of Soil Ecology, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany,3
Centre Régional pour l'Eau Potable et l'Assainissement à Faible Cou
, Siège Régional, BP 7112, Ouagadougou 03, Burkina Faso,4
SeqBio-IRD Ensam, 2 Place Viala, Bâtiment 12, 34060 Montpellier Cedex 2, France5
Received 22 December 2008/ Accepted 1 June 2009
The effect of agricultural management practices on geochemical cycles in moderate ecosystems is by far better understood than in semiarid regions, where fertilizer availability and climatic conditions are less favorable. We studied the impact of different fertilizer regimens in an agricultural long-term observatory in Burkina Faso at three different plant development stages (early leaf development, flowering, and senescence) of sorghum cultivars. Using real-time PCR, we investigated functional microbial communities involved in key processes of the nitrogen cycle (nitrogen fixation, ammonia oxidation, and denitrification) in the rhizosphere. The results indicate that fertilizer treatments and plant development stages combined with environmental factors affected the abundance of the targeted functional genes in the rhizosphere. While nitrogen-fixing populations dominated the investigated communities when organic fertilizers (manure and straw) were applied, their numbers were comparatively reduced in urea-treated plots. In contrast, ammonia-oxidizing bacteria (AOB) increased not only in absolute numbers but also in relation to the other bacterial groups investigated in the urea-amended plots. Ammonia-oxidizing archaea exhibited higher numbers compared to AOB independent of fertilizer application. Similarly, denitrifiers were also more abundant in the urea-treated plots. Our data imply as well that, more than in moderate regions, water availability might shape microbial communities in the rhizosphere, since low gene abundance data were obtained for all tested genes at the flowering stage, when water availability was very limited.
* Corresponding author. Mailing address: Helmholtz Zentrum München, German Research Center for Environmental Health, Department of Terrestrial Ecogenetics, Institute of Soil Ecology, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany. Phone: 49 89 3187 3479. Fax: 49 89 3187 3376. E-mail: brigitte.hai{at}helmholtz-muenchen.de
Published ahead of print on 5 June 2009.
Applied and Environmental Microbiology, August 2009, p. 4993-5000, Vol. 75, No. 15
0099-2240/09/$08.00+0 doi:10.1128/AEM.02917-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
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