title: Quantification of key genes steering the microbial nitrogen cycle in the rhizosphere of sorghum cultivars in tropical agroecosystems.
abstract: 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.
authors.affiliation: Helmholtz Zentrum München, German Research Center for Environmental Health, Department of Terrestrial Ecogenetics, Institute of Soil Ecology, Neuherberg, Germany. brigitte.hai@helmholtz-muenchen.de
authors.forename: Brigitte
authors.initials: B
authors.lastname: Hai
authors.forename: Ndeye Hélène
authors.initials: NH
authors.lastname: Diallo
authors.forename: Saidou
authors.initials: S
authors.lastname: Sall
authors.forename: Felix
authors.initials: F
authors.lastname: Haesler
authors.forename: Kristina
authors.initials: K
authors.lastname: Schauss
authors.forename: Moussa
authors.initials: M
authors.lastname: Bonzi
authors.forename: Komi
authors.initials: K
authors.lastname: Assigbetse
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Chotte
authors.forename: Jean Charles
authors.initials: JC
authors.lastname: Munch
authors.forename: Michael
authors.initials: M
authors.lastname: Schloter
mesh_terms: D001105:Archaea / Q000378:metabolism*; D001419:Bacteria / Q000378:metabolism*; D044822:Biodiversity; D002050:Burkina Faso; D019641:DNA, Archaeal / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D017753:Ecosystem; D005308:Fertilizers; D019766:Genes, Archaeal; D005798:Genes, Bacterial; D053858:Metabolic Networks and Pathways / Q000235:genetics; D009584:Nitrogen / Q000378:metabolism*; D018517:Plant Roots / Q000382:microbiology*; D012988:Soil Microbiology; D045868:Sorghum / Q000382:microbiology*
chemical_list: D019641:DNA, Archaeal; D004269:DNA, Bacterial; D005308:Fertilizers; D009584:Nitrogen