title: Phytochemical analysis of mature tree root exudates in situ and their role in shaping soil microbial communities in relation to tree N-acquisition strategy.
abstract: Eperua falcata (Aublet), a late-successional species in tropical rainforest and one of the most abundant tree in French Guiana, has developed an original strategy concerning N-acquisition by largely preferring nitrate, rather than ammonium (H. Schimann, S. Ponton, S. Hättenschwiler, B. Ferry, R. Lensi, A.M. Domenach, J.C. Roggy, Differing nitrogen use strategies of two tropical rainforest tree species in French Guiana: evidence from (15)N natural abundance and microbial activities, Soil Biol. Biochem. 40 (2008) 487-494). Given the preference of this species for nitrate, we hypothesized that root exudates would promote nitrate availability by (a) enhancing nitrate production by stimulating ammonium oxidation or (b) minimizing nitrate losses by inhibiting denitrification. Root exudates were collected in situ in monospecific planted plots. The phytochemical analysis of these exudates and of several of their corresponding root extracts was achieved using UHPLC/DAD/ESI-QTOF and allowed the identification of diverse secondary metabolites belonging to the flavonoid family. Our results show that (i) the distinct exudation patterns observed are related to distinct root morphologies, and this was associated with a shift in the root flavonoid content, (ii) a root extract representative of the diverse compounds detected in roots showed a significant and selective metabolic inhibition of isolated denitrifiers in vitro, and (iii) in soil plots the abundance of nirK-type denitrifiers was negatively affected in rhizosphere soil compared to bulk. Altogether this led us to formulate hypothesis concerning the ecological role of the identified compounds in relation to N-acquisition strategy of this species.
authors.affiliation: Université Lyon1, CNRS, UMR5557, INRA, USC1364, Ecologie Microbienne, Centre d'Etude des Substances Naturelles, Villeurbanne F-69622, France; Université Lyon1, CNRS, UMR5557, INRA, USC1364, Ecologie Microbienne, Groupes Fonctionnels Microbiens et Cycle de l'Azote, Villeurbanne F-69622, France. Electronic address: sergemichalet@yahoo.fr.
authors.forename: Serge
authors.initials: S
authors.lastname: Michalet
authors.forename: Julien
authors.initials: J
authors.lastname: Rohr
authors.forename: Denis
authors.initials: D
authors.lastname: Warshan
authors.forename: Clément
authors.initials: C
authors.lastname: Bardon
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Roggy
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Domenach
authors.forename: Sonia
authors.initials: S
authors.lastname: Czarnes
authors.forename: Thomas
authors.initials: T
authors.lastname: Pommier
authors.forename: Bruno
authors.initials: B
authors.lastname: Combourieu
authors.forename: Nadine
authors.initials: N
authors.lastname: Guillaumaud
authors.forename: Floriant
authors.initials: F
authors.lastname: Bellvert
authors.forename: Gilles
authors.initials: G
authors.lastname: Comte
authors.forename: Franck
authors.initials: F
authors.lastname: Poly
mesh_terms: D009584:Nitrogen / Q000378:metabolism; D053147:Plant Exudates / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism*; D014197:Trees / Q000378:metabolism*
chemical_list: D053147:Plant Exudates; D009584:Nitrogen
keywords: Chemical ecology; Denitrification; Eperua falcata; Metabolic profiling; Mycorrhizae; Plant–microbes interactions; Root exudates