Description succincte
(Anglais)
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The proposed project has the overall goal to use molecular markers (16S rDNA, amoA and nifH) for the characterisation of key microbial populations in the rhizosphere of Norway spruce at high spatial resolution by (1) investigating nitrifying and nitrogen-fixing bacteria in the rhizosphere and non-rhizosphere soil, and (2) by detecting shifts in these microbial populations and in the amoA and nifH activities caused by metal stress.
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Partenaires et organisations internationales
(Anglais)
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AT, BE, BG, CY, CZ, DK, FI, FR, DE, EL, HU, IE, IT, NL, NO, PL, SK, SI, ES, SE, CH, UK
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Résumé des résultats (Abstract)
(Anglais)
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In this study we assessed the effects of heavy metal (HM) contamination and subsequent remediation by poplar (Populus deltoides) on the Pseudomonas and ammonia-oxidizing bacterial communities. We hypothesized that (i) HM would affect community function and alter the microbial community structure and (ii) phytostabilization would lead to restoration of the original soil microbial communities when the HMs are partly removed. These hypotheses were tested in a compartment device constructed from soil with a medium history of heavy metal contamination. Using such devices, we quantified microbial activity and analysed bacterial community dynamics in the root and the root-free compartments and compared planted-polluted, planted-unpolluted, and unplanted-polluted devices. Bulk and rhizosphere soils were sampled 1, 30, 60 and 90 days after planting poplar seedlings. Group-specific primers for Pseudomonas and ammonia-oxidizing bacteria (AOB) were used to PCR-amplify specific 16S rRNA and amoA gene fragments from soil DNA extracts and were analysed by denaturing gradient gel electrophoresis (DGGE). DGGE profiles of Pseudomonas and AOB revealed higher numbers of bands in the non-contaminated compared to the heavy-metal contaminated soil samples and principal component analysis of DGGE profiles clearly separated HM contaminated from non-contaminated soil bacterial communities. In addition, root growth have also influenced the bacterial communities, whereas a clear rhizosphere effect was only observed for AOB but not for Pseudomonas. Cloning and sequencing of dominant DGGE bands revealed for AOB that all sequences were related to Nitrosospira spp. At the end of the experiment, the root compartments of the HM contaminated soils were significantly depleted in HM compared to the bulk compartments indicating high HM uptake by poplar roots. The AOB and Pseudomonas community structure in the root-free compartments of the HM contaminated soil remained markedly different from that in the control soils during phytoremediation but in the rhizosphere soil the community became similar with time and removal of HMs by plant uptake. The results suggest that AOB and Pseudomonas community structure recovered after removal of HM.
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