Rhizosphere in space and time – challenges for designing the most relevant root traits for efficient nutrient acquisition

[début du texte]The rhizosphere, i.e. the soil volume that is influenced by the activities of living roots, has been largelydocumented for its pivotal role in plant nutrition, and thus ecological significance in terrestrial ecosystems (e.g.Hinsinger et al., 2009). The number of studies on the fate of nutrients in the rhizosphere, especiallyphosphorus amongst major nutrients, iron and zinc amongst micronutrients, has considerably increased overthe past decades, as revealed by the published literature. However, much of our understanding of theunderlying rhizosphere processes rely on microcosm experiments in more or less artificial conditions. Incontrast, we still lack comprehensive studies of the rhizosphere of field-­‐grown plants that includes both itsspatial and temporal dimensions. The aim of this keynote lecture is to address these two facets that challengeour capacity to predict plant nutrition and to manipulate such rhizosphere properties for the purpose of anecological intensification of agroecosystems

Thermodynamic modelling of P availability: the case of intercropping rhizosphere

Plants of chickpea and durum wheat were cultivated as sole-­‐crop and intercrop in a rhizobox deviceaccording to a substitutive design. Unplanted soil was used as a control treatment. The soil used was a noncarbonated Luvisol with a neutral pH. Plants were harvested at the chickpea flowering stage. The pH, Pavailability and dissolved Ca were measured in soil as extracted by water and CaCl2 (1 and 10 mM). A set ofthermodynamic models were used (i.e. CD MUSIC; Nica Donnan; ion exchange) to simulate and understandmeasured P availability variations in each treatment

Interactions entre céréale et légumineuse en association et acquisition de phosphore du sol (processus rhizosphériques sous-jacents)

L'objectif de cette étude a été de préciser l'implication des processus rhizosphériques dans lesinteractions pour l'acquisition de phosphore (P) entre une céréale et une légumineuse enassociation. Nous avons proposé comme mécanisme de facilitation l'acidification de la rhizosphèredes espèces en association induite par la fixation de N2 de la légumineuse dans le cas de sol neutres àalcalins. Ainsi, l'étude s'est focalisée sur l'influence des changements de pH induits par les racines.Les effets de la disponibilité initiale en P du sol ainsi que de la distance entre les racines des espècesassociées ont également été testés. Les expérimentations ont été menées au champ ainsi qu'enconditions contrôlées. Le blé dur et différentes légumineuses ont été cultivés en culturemonospécifique ou en association sur un même sol pour toutes les expérimentations. Le sol neutreutilisé (Luvisol) présentait trois niveaux contrastés de fertilisation phosphatée et provenait desparcelles d'un essai de longue durée. Nous avons pu démontrer que la manipulation des interactionsrhizosphériques entre une céréale et une légumineuse en association pouvait être optimisée pourpermettre l'augmentation de la disponibilité en P dans la rhizosphère des espèces associées, etencore plus dans le cas de sols présentant une faible valeur initiale de disponibilité. Lescaractéristiques du sol ont eu un rôle clé dans la détermination des processus rhizosphériquesimpliqués. Dans notre cas, les changements de pH induits par les racines ont permis d'augmenter defaçon substantielle la disponibilité en P suite à une acidification, mais aussi à une alcalinisation de larhizosphère. Ainsi la légumineuse, mais aussi la céréale sont susceptibles de faciliter l'acquisition del'espèce associée. Les interactions relatives au pH peuvent influencer la disponibilité en P sur unedistance de plusieurs millimètres et ainsi améliorer l'acquisition de P des plantes à proximité del'espèce facilitatrice.Mots clés : culture associée, facilitation, rhizosphère, disponibilité, phosphore, pH, racineThe aim of the study was to elucidate the implication of rhizospheric processes on plant speciesinteractions for phosphorus (P) acquisition between a cereal and a legume, when intercropped. Weproposed that root-induced acidification of the rhizosphere by the intercropped legume due to N2-fixation as a mechanism of facilitation in neutral to alkaline soils. Thus, the study focused on rootinducedchanges of pH. The effects of initial soil P availability and distance between roots ofintercropped species were also tested. In order to achieve our goals, experiments in the field and incontrolled condition for several cropping devices were conducted. Durum wheat and differentlegumes were grown as sole crops and intercropped on the same soil for all the experiments. Weused a neutral soil (Luvisol) presenting three contrasted fertilization rates from the field of a longtermP fertilizer trial. We demonstrated that cereal-legume can be used to enhance P availability, andeven more so in low P soils, through managing rhizospheric interactions to optimize P acquisition ofintercropped species. Soil characteristics are also a key factor determining the influence of thoserhizospheric processes. In our studied soil root-induced changes of pH substantially enhanced Pavailability in the rhizosphere either through acidification or alkalization. Thus the legume but alsothe cereal may facilitate the acquisition of the intercropped species. Interactions involving pH canaffect P availability over distance of several millimeters and ultimately enhance P acquisition ofplants in the surrounding of the facilitative species.Key words: intercrop, facilitation, rhizosphere, availability, phosphorus, pH, rootMONTPELLIER-SupAgro La Gaillarde (341722306) / SudocSudocFranceF

Proceedings of the First SolACE Stakeholder Event

This document provides an overview of the proceedings of the first SolACE stakeholder event

Rhizosphere microbial community in intercropped durum wheat and faba bean as affected by phosphorus fertilizer history

The experiment was conducted in the long term P fertilizer trial of INRA research centre at Auzeville(43.5oN, 1.43oE) in south western France. The three P regimes corresponded to fertilizer levels applied since1968: P0 (no fertilization), P1 (fertilization rate to balance the mean annual P removal by crops) and P4(fertilization rate representing three-­‐ to four-­‐fold that of P1). Durum wheat and faba bean were grown aloneor as durum wheat/faba bean intercrops in this field trial. Their rhizospheres were collected at the faba beanflowering stage, as well as the corresponding bulk soils. Soil DNA and RNA were extracted in these varioussamples and qPCR was used to assess the number of gene copies of fungi, bacteria, as well as several bacterialphyla (Actinobacteria, α-­‐Proteobacteria and Firmicutes (strongly dominated with P-­‐cycling taxa)) and betapropeller phytase (BPP)

Proceedings of the Second SolACE Stakeholder Event

The Second Stakeholder Event of the project SolACE - Solutions for improving Agroecosystem and Crop Efficiency for water and nutrient use - took place on May 16, 2018 in Foggia, Italy. During the second SolACE stakeholder event, SolACE project partners presented innovations that are being tested in the project with the aim to receive feedback and comments

Améliorer la biodisponibilité du phosphore : comment valoriser les compétences des plantes et les mécanismes biologiques du sol ?

Les ions orthophosphates (Pi) représentent les seules formes de phosphore (P) utilisable par les cultures. Dans les sols, ils sont généralement présents à de faibles concentrations dans la solution, en raison des nombreux processus géochimiques contraignant leur mobilité et disponibilité. Les plantes et les micro - organismes associés, au travers de relations rhizosphériques, symbiotiques et par la prédation des populations microbiennes, modifient considérablement la quantité de P que la plante est capable d'acquérir tout au long de sa croissance (biodisponibilité). Cette revue décrit les différents processus (modifications des racines, rôle du pH, des anions organiques, des enzymes, de la microfaune et de la macrofaune) qui peuvent modifier la biodisponibilité du P dans la rhizosphère. Des pistes pour mieux valoriser le potentiel intrinsèque des végétaux et de l'écologie des organismes du sol et optimiser l'acquisition de P des cultures à partir du sol sont proposées. (Résumé d'auteur

Diversity and P-solubilizing ability of mycorrhizosphere bacteria associated with Pinus pinaster in the Landes forest ecosystem

Ectomycorrhizal fungi (ECM) and their associated mycorrhizosphere bacteria (MB) play a major role in phosphorous (P) nutrition of maritime pine, particularly in the Landes forest ecosystem considering the low bioavailability of P in its sandy-acidic soils. In order to characterize the MB associated to ECM, three collection campaigns of ECM root tips were performed from autumn 2005 to autumn 2006 throughout three forest stations. Five MB and nine ECM genera were identified overall through sequencing of 16S rDNA and mitochondrial large subunit rDNA fragment respectively. Dramatic seasonal changes were observed in the different MB-ECM associations especially in Burkholderia-Lactarius and Bacillus-Russula that were the most abundant ones. P-solubilizing ability of MB was shown to be taxon-dependent with a large majority of P-solubilizing isolates among Burkholderia, Pseudomonas and Paenibacillus contrary to Bacillus. Relationships between functional diversity of the MB-ECM associations and bioavailability of soil P remain to be investigated. (Résumé d'auteur)