Éditeur(s) : HAL CCSD Elsevier
Résumé : 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. Hattenschwiler, 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 N-15 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. (C) 2013 Elsevier Masson SAS. All rights reserved.
ISSN: 0981-9428

hal-01032437
https://hal.archives-ouvertes.fr/hal-01032437
DOI : 10.1016/j.plaphy.2013.05.003

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Nitrogen (N) transfer from legume trees to associated crops is a key factor for the N economy of low-input agroforestry systems. In this work, we presented a new approach to estimate N transfer based on the 15N content of root exudates and N released by root turnover of the donor plant (Gliricidia sepium) and the temporal change of the 15N content of the receiver plant (Dichanthium aristatum). The study was carried out in greenhouse using two isotopic methods: 15N leaf feeding (LF) and the natural 15N abundance (NA). Measurements of exudate 15N were made at several dates before and after tree pruning. A time-dependent box model was devised to quantify N transfer in time and to make comparisons between the isotopic methods. In NA, although tree roots and exudates presented a similar 15N signature before tree pruning, exudates were strongly depleted in 15N after pruning. In LF, exudates were always depleted in 15N in relation to tree roots. Hence, the current assumption used in N transfer studies concerning the equal 15N/14N distribution in tissues of the donor plant and in its excreted N was not confirmed in our study. Before pruning, N transfer functioned as a two-N-source system (soil N and exudates N) and both isotopic methods provided similar estimates: 11–12% for LF and 10–15% for NA. Calculations performed with the model indicated that N transfer occurred with small or nil fractionation of 15N in exudates. After pruning, there was a third N source associated with N released from tree root turnover. During this period, the isotopic signature of the receiver plant showed a transient state due to the progressive decrease of 15N content of that N source. The amount of N derived from the tree represented 65% of the total N content of the grass at the end of the experiments.
ISSN: 1161-0301

hal-01082183
https://hal-agroparistech.archives-ouvertes.fr/hal-01082183
DOI : 10.1016/j.eja.2007.03.003

Résumé : Dans le cadre de la promotion de systèmes de culture alternatifs à moindres intrants chimiques, des études sur l'introduction de plantes de service ayant vocation à réduire l'usage des pesticides et engrais azotés mobilisent un effort de recherche considérable. Dans le cadre de la production bananière pour laquelle la nuisibilité causée par les nématodes phytoparasites constitue l'une des principales contraintes, une des principales alternatives à l'utilisation de nématicides chimiques repose sur l'usage raisonné en rotation ou en association culturale de plantes de service à propriétés nématorégulatrices. Parmi les espèces candidates, celles du genre Crota/aria spp. ont largement été étudiées en raison de leur aptitude à contrôler les nématodes phytoparasites. Une méta-analyse révèle cependant que même si de nombreux auteurs s'accordent à reconnaître les propriétés allélopathiques des plantes de cette espèce, ils sont également enclins à reconnaître la forte variabilité d'expression de ces propriétés vis-à-vis du contrôle des nématodes selon les situations expérimentées. L'objectif de ce travail repose sur la compréhension du déterminisme biochimique des exsudats. La stratégie expérimentale mise en oeuvre a consisté à tester en conditions contrôlées le comportement biochimique des exsudats racinaires de deux espèces de crotalaires (C retusa, C spectabilis) et d'une espèce sensible, le bananier dessert (Musa spp.) en fonction i) de conditions biotiques variées -i.e. présence ou non de nématodes (Radopholus similis et Meloidogyne arenariaï, et présence ou non de mycorhizes-, ii) de conditions abiotiques contrastées -i.e. utilisation d'un sol naturel vs. substrat neutre, ajout ou non d'engrais chimique. La méthodologie innovante des «plantes à traire » (Brevet INRA) a été requise pour pouvoir travailler sur les exsudats racinaires des plantes conditionnées plutôt que sur des Iixiviats, comme réalisé dans des expérimentations antérieures.Les résultats obtenus en spectrophométrie visible montrent que la modification des conditions abiotiques affecte de manière importante les profils biochimiques des plantes étudiées. En présence du nématode 1..·1. arenaria les profils biochimiques des deux crotalaires sont également modifiés. Des biotests réalisés à l'aide des exsudats racinaires conditionnés au préalable par les modifications biotiques ont permis de démontrer l'effet nématostatique des crotalaires. Des analyses biochimiques en Ge-MS mettent en évidence de manière plus précise des molécules actives mises en jeu sous différentes modalités biotiques et abiotiques. Ces recherches, de portée générique, permettront de mieux comprendre les conditions de l'environnement qui régulent les profils biochimiques des exsudats racinaires des crotalaires et par extension, seront applicables aux recherches menées sur d'autres plantes de service candidates. Ceci aidera, à terme, à définir les conditions environnementales à réunir, pour orienter de manière optimale les effets allélopathiques dans une perspective de nématorégulation naturelle
As part of the promotion of alternative cropping systems at lower chemical inputs, studies on the introduction of cover crops designed to reduce the use of pesticides and nitrogen fertilizers mobilize a considerable research effort. Under banana production for which the hannfu1ness caused by plant-parasitic-nematodes is one ofthe main constraints, one of the main alternatives to the use ofchemical nematicides is based on the rational use in rotation or intercropping of cover rI crops to proteet crops from plant-parasitic-nematodes, Among the candidate species, the species from the genus of Crota/aria spp. have been widely studied because of their ability to control plant parasitic-nematodes. A meta-analysis reveals that although many authors agree allelopathic properties of these species, they are also likely to recognize the high variability of expression of these properties vis-àvis the control of nematodes according to the situations experieaced.. The objective of this woIk is focnsed on the onderstanding of the biochemical determinism of mot exudates onder environment biotic and abiotic variations. The experimental strategy was 10 test onder controlled conditions the biochemical behavior of mot exudates of two species of crotalarias (C retusa, C. spectabilis) and a susceptible species, the dessert banana crop (Musa spp.) with i) modification ofbiotic conditions -ie presence or absence of nematodes iMeloidogyne arenaria and Radopho/us similis), and presence or absence of mycorrhiza-ii) contrasting abiotic conditions -ie using a natural soil vs. neutral substrate, whether to add fertilizer. The innovative methodology of "milking plants" (patent INRA) was required in order to work on the root exudates of plants packed rather thanleachate, as done in previous experiments. The results obtained show that 'visible spectrophotometry changing abiotic conditions affect significantly the biochemical profiles of the studied plants. In the presence of nematode M. arenaria biochemical profiles of both crotalarias are also changed. Bioassays conducted using mot exudates conditioned in advance by biotic changes have demonstrated the effect of nématostatique crotalarias. Biochemical Ge-MS demonstrate more clearly active molecules that are involved in varions biotic and abiotic conditions. This research, generic scope, to better understand the environmental conditions that regulate biochemical profiles of mot exudates crotalarias and by extension, will apply to research on other plants service candidates. This will ultimately define the environmental conditions to meet, to guide optimal allelopathic effects from the perspective ofnatural nématorégulation

http://www.theses.fr/2012AGUY0561/document