Nematofauna as indicator of soil N availability in mixed plantations? A case study from tropical forest of Eucalyptus and Acacia in Congo. [P2.179]

Nitrogen is a limiting factor for the growth of Eucalyptus plantations, particularly in subtropical areas characterized by very low soil fertility (e.g.degraded pastures). The association with N2- fixing species such as Acacia mangium is an alternative for ecological intensification of these ecosystems. Enhancement of Eucalyptus trees growth may happen by direct transfer of N fixed by Acacia trees or indirectly through litter decomposition. Field assessments in Congo showed that the productivity of Eucalyptus trees in mixed plantations was significantly increased compared with Eucalyptus alone. Higher N contents in soil of mixed plantations explained such positive impact. In a microcosm experiment, we measured N mineralization in soil sampled from pure stands of Acacia, pure stands of Eucalyptus and from the mixed plantations. The results showed an accumulation of nitrate in the rhizosphere of Acacia. We found that the introduction of Acacia trees changed significantly the structure of the community of nematodes by increasing the proportion of bacterial-feeding nematodes. Similar results were obtained in mixed-plantations in Brazil and in France, suggesting that nematofauna could be a key indicator of N availability in soil. Microbial communities involved in nitrification were also studied by targeting AOA and AOB genes using the quantitative PCR method. An increase of the number of copies of AOA gene was observed in the rhizosphere of Acacia while AOB gene was difficult to detect. This suggests that Archae communities may play an important role in N cycling in soil of Eucalyptus plantations. Our results demonstrate that the introduction of Acacia in mixed plantations systems influences the N cycle in the soil and associated biological activities. (Résumé d'auteur

Cd localisation and speciation in a contaminated sediment and in the Znand Cd hyperaccumulating plant Arabidopsis halleri

International audienceThe purpose of this work was to characterise the chemical speciation of Cd in a Zn- and Cd-contaminated dredged sediment subjected to a phytoremediation treatment with the hyperaccumulator plant Arabidopsis halleri

Is phytoextraction a suitable green treatment for metal-contaminated sediments ?

International audienceThe cleaning of waterways by regular dredging generates great volumes of sediments and, owing to human activities, these sediments often contain large amounts of metals. These materials are usually spread on landfill sites. Phytoremediation could be a stategy for the reclamation of these polluted sediments. To our knowledge, phytoextraction with hyperaccumulating plants has been few tested on contaminated sediment. This work focuses on the mechanisms of Cd accumulation in Arabidopsis halleri, a Cd and Zn hyperaccumulator, and the effects of this species on a metal polluted sediment

Draft Genome Sequence of the Flagellated Xanthomonas fuscans subsp. fuscans Strain CFBP 4884

Article de revue (Article scientifique dans une revue à comité de lecture)International audienceWe report the draft genome sequence of the flagellated strain CFBP 4884 of Xanthomonas fuscans subsp. fuscans, which was isolatedin an outbreak of common bacterial blight of beans along with non-flagellated strains. Comparative genomics will allowone to decipher the genomic diversity of strains cohabiting in epidemics.</p