A baixa eficiência da adubação fosfatada em solos altamente intemperizados é devido, entre outros fatores, à adsorção do fósforo (P) à superfície das argilas silicatadas do tipo 1:1 e, principalmente, dos (hidr)óxidos de Fe e de Al. Manejos do solo que induzem a solubilização de formas de P indisponíveis para as plantas têm sido intensamente estudados nos últimos anos. Uma tentativa de aumentar a concentração de P disponível na solução do solo para sua absorção pelas plantas é a mobilização de P por ânions de ácidos orgânicos de baixa massa molar (AOBMM). Ânions derivados de AOBMM exsudados pelas raízes de plantas ou excretados por microrganismos são associados com algumas condições de rizosfera como deficiência de P e fitotoxidez de Al e interagem com o solo de forma a aumentar a biodisponibilidade de P. Dependendo dos atributos do solo, do grau de dissociação, das propriedades e do número de grupos carboxílicos dos ânions orgânicos, o P pode ser mobilizado do solo principalmente devido à dissolução complexométrica de minerais e à adsorção competitiva dos grupos funcionais carboxílicos e fosfato nos sítios de superfície coloidais. A capacidade dos ânions citrato, malato e oxalato em mobilizar P de amostras de um Neossolo Quartzarênico típico (RQ) e de um Latossolo Vermelho ácrico (LVwf) foi avaliada por meio de um estudo de lixiviação de ânions em colunas. Devido a não detecção de P nos efluentes das colunas com LVwf, foi realizado outro estudo em colunas, no qual somente citrato foi lixiviado, mas num volume maior, e as alterações das formas de P nas amostras desse solo induzidas pela lixiviação de citrato foram identificadas por espectroscopia de absorção de raios-X na borda K do fósforo (X-ray absorption near edge structure -XANES - spectroscopy). A capacidade dos ânions de AOBMM em solubilizar P foi mais dependente do teor de P disponível e de outros atributos do solo que do número de grupos funcionais carboxílicos dos ânions orgânicos. Somente o oxalato mobilizou P do RQ, enquanto todos os ânions de AOBMM foram capazes de mobilizar P do LVwf. Quando baixos volumes de solução contendo ânions de AOBMM foram lixiviados no solo, além do aumento do pH, a mobilização de P foi acompanhada pela mobilização de Al no RQ (pH água = 5), e pela mobilização de Ca no LVwf (pH água = 5.6), o que indica solubilização de P pela complexação de Al, Ca, ou Fe, de fosfatos insolúveis, ou pela inibição da precipitação de P com esses metais. Ao lixiviar um volume maior de citrato no LVwf, o P também não foi detectado nos efluentes das colunas, mas houve lixiviação intensa de Al e Fe, bem como mudanças nas proporções de formas de P no solo caracterizadas pelos espectros XANES. Embora tenhamos encontrado indícios da ação dos principais mecanismos de solubilização de P (dissolução complexométrica de minerais e troca de ligantes entre grupos funcionais carboxílicos e P adsorvido ao solo), os ânions de AOBMM mostraram pouco potencial de efetivamente aumentar a biodisponibilidade de P. / Phosphate fertilization of acidic, highly weathered soils is inefficient because of the adsorption of phosphorus (P) to 1:1 silicate clays and, especially, to Fe and Al oxides. Different soil management practices to induce solubilization of unavailable forms of P to plants nutrition have been intensively studied in recent years. The mobilization of P with anions of low molecular weight organic acids (LMWOA) increases the concentration of available P in the soil solution for plant uptake. Anions derived from LMWOA exudates from plants root or excreted by microbes are associated with some rhizosphere conditions, as deficiency of P and Al phytotoxicity, and they interact with the soil in order to increase P availability. Depending on the soil attributes, and degree of dissociation, properties, and number of carboxyl groups from organic anions, P can be mobilized from soil mainly because of complexometric dissolution of soil minerals and ligand exchange of functional carboxyl groups and P adsorbed in soil surface sites. The capacity of citrate, malate and oxalate anions to mobilize P from a Typic Quartzipsamment (RQ) and an Anionic Acrudox (LVwf) was evaluated in a column leaching study. Because no P was detectable in columns effluents from LVwf, another column leaching study was performed, but only citrate was leached with a greater volume of solution, and citrate-induced changes at P forms in the soil were identified by P K-edge X-ray absorption near edge structure - XANES - spectroscopy. The capacity of LMWOA anions to solubilize P was more dependent of P status and other soil attributes, than number of carboxyl groups of organic anions. Only oxalate mobilized P from RQ, and all LMWOA anions were able to mobilize P from LVwf. Increasing of P mobilization and soil pH were followed by increases of Al mobilization from RQ (pH water = 5), and Ca mobilization from LVwf (pH water = 5.6) at lower volumes of LMWOA anions leaching. Phosphorus was solubilized by complexation of Al, Ca or Fe from insoluble phosphate minerals, or by inhibition of Al, Ca or Fe phosphate precipitation. After leaching a greater volume of citrate through LVwf, P was still undetectable in effluents from columns, but there was an intensively leaching of Al and Fe, as well as changes in proportions of adsorbed P characterized in soil XANES spectra. Although we have found evidences about the action of main mechanisms of P solubilization (complexometric dissolution, and ligand exchange of carboxylic functional groups for adsorbed P on soil minerals) by LMWOA anions, they had a little potential to really increase P availability.

A baixa eficiência da adubação fosfatada em solos altamente intemperizados é devido, entre outros fatores, à adsorção do fósforo (P) à superfície das argilas silicatadas do tipo 1:1 e, principalmente, dos (hidr)óxidos de Fe e de Al. Manejos do solo que induzem a solubilização de formas de P indisponíveis para as plantas têm sido intensamente estudados nos últimos anos. Uma tentativa de aumentar a concentração de P disponível na solução do solo para sua absorção pelas plantas é a mobilização de P por ânions de ácidos orgânicos de baixa massa molar (AOBMM). Ânions derivados de AOBMM exsudados pelas raízes de plantas ou excretados por microrganismos são associados com algumas condições de rizosfera como deficiência de P e fitotoxidez de Al e interagem com o solo de forma a aumentar a biodisponibilidade de P. Dependendo dos atributos do solo, do grau de dissociação, das propriedades e do número de grupos carboxílicos dos ânions orgânicos, o P pode ser mobilizado do solo principalmente devido à dissolução complexométrica de minerais e à adsorção competitiva dos grupos funcionais carboxílicos e fosfato nos sítios de superfície coloidais. A capacidade dos ânions citrato, malato e oxalato em mobilizar P de amostras de um Neossolo Quartzarênico típico (RQ) e de um Latossolo Vermelho ácrico (LVwf) foi avaliada por meio de um estudo de lixiviação de ânions em colunas. Devido a não detecção de P nos efluentes das colunas com LVwf, foi realizado outro estudo em colunas, no qual somente citrato foi lixiviado, mas num volume maior, e as alterações das formas de P nas amostras desse solo induzidas pela lixiviação de citrato foram identificadas por espectroscopia de absorção de raios-X na borda K do fósforo (X-ray absorption near edge structure -XANES - spectroscopy). A capacidade dos ânions de AOBMM em solubilizar P foi mais dependente do teor de P disponível e de outros atributos do solo que do número de grupos funcionais carboxílicos dos ânions orgânicos. Somente o oxalato mobilizou P do RQ, enquanto todos os ânions de AOBMM foram capazes de mobilizar P do LVwf. Quando baixos volumes de solução contendo ânions de AOBMM foram lixiviados no solo, além do aumento do pH, a mobilização de P foi acompanhada pela mobilização de Al no RQ (pH água = 5), e pela mobilização de Ca no LVwf (pH água = 5.6), o que indica solubilização de P pela complexação de Al, Ca, ou Fe, de fosfatos insolúveis, ou pela inibição da precipitação de P com esses metais. Ao lixiviar um volume maior de citrato no LVwf, o P também não foi detectado nos efluentes das colunas, mas houve lixiviação intensa de Al e Fe, bem como mudanças nas proporções de formas de P no solo caracterizadas pelos espectros XANES. Embora tenhamos encontrado indícios da ação dos principais mecanismos de solubilização de P (dissolução complexométrica de minerais e troca de ligantes entre grupos funcionais carboxílicos e P adsorvido ao solo), os ânions de AOBMM mostraram pouco potencial de efetivamente aumentar a biodisponibilidade de P. / Phosphate fertilization of acidic, highly weathered soils is inefficient because of the adsorption of phosphorus (P) to 1:1 silicate clays and, especially, to Fe and Al oxides. Different soil management practices to induce solubilization of unavailable forms of P to plants nutrition have been intensively studied in recent years. The mobilization of P with anions of low molecular weight organic acids (LMWOA) increases the concentration of available P in the soil solution for plant uptake. Anions derived from LMWOA exudates from plants root or excreted by microbes are associated with some rhizosphere conditions, as deficiency of P and Al phytotoxicity, and they interact with the soil in order to increase P availability. Depending on the soil attributes, and degree of dissociation, properties, and number of carboxyl groups from organic anions, P can be mobilized from soil mainly because of complexometric dissolution of soil minerals and ligand exchange of functional carboxyl groups and P adsorbed in soil surface sites. The capacity of citrate, malate and oxalate anions to mobilize P from a Typic Quartzipsamment (RQ) and an Anionic Acrudox (LVwf) was evaluated in a column leaching study. Because no P was detectable in columns effluents from LVwf, another column leaching study was performed, but only citrate was leached with a greater volume of solution, and citrate-induced changes at P forms in the soil were identified by P K-edge X-ray absorption near edge structure - XANES - spectroscopy. The capacity of LMWOA anions to solubilize P was more dependent of P status and other soil attributes, than number of carboxyl groups of organic anions. Only oxalate mobilized P from RQ, and all LMWOA anions were able to mobilize P from LVwf. Increasing of P mobilization and soil pH were followed by increases of Al mobilization from RQ (pH water = 5), and Ca mobilization from LVwf (pH water = 5.6) at lower volumes of LMWOA anions leaching. Phosphorus was solubilized by complexation of Al, Ca or Fe from insoluble phosphate minerals, or by inhibition of Al, Ca or Fe phosphate precipitation. After leaching a greater volume of citrate through LVwf, P was still undetectable in effluents from columns, but there was an intensively leaching of Al and Fe, as well as changes in proportions of adsorbed P characterized in soil XANES spectra. Although we have found evidences about the action of main mechanisms of P solubilization (complexometric dissolution, and ligand exchange of carboxylic functional groups for adsorbed P on soil minerals) by LMWOA anions, they had a little potential to really increase P availability.

La formation argileuse du Callovo-Oxfordien (COx) est étudiée comme possible roche-hôte d’un stockage profond de déchets radioactifs (projet Cigéo). En effet, en plus d’être très faiblement perméable, elle présente une forte teneur en minéraux argileux, capables de retenir les radionucléides sous forme cationique et d’en retarder ainsi fortement leur transport. Néanmoins, certains colis de déchets sont susceptibles de relarguer d’importante quantité de molécules organiques, capables de complexer ces radionucléides et d’augmenter leur mobilité. Aussi, l’objectif de ce travail a été de mieux comprendre le comportement diffusif de plusieurs molécules organiques d’intérêt vis à vis de cette roche argileuse, en investiguant dans un premier temps leur affinité avec la roche hôte. La rétention de molécules organiques sous forme anionique (acétate, phtalate, adipate, benzoate, citrate) a été quantifiée sur la roche argileuse du COx dispersée à l’aide d’expériences d’adsorption/désorption en batch. Des expériences sur roche décarbonatée et fraction de faible granulométrie ont également été réalisées afin de mettre en évidence les phases de la roche et les fonctions chimiques responsables de la rétention. L’intensité de la rétention, Rd, a pu être corrélée avec le moment dipolaire, µ(Orga.), pour fournir une estimation qualitative de la rétention de molécules organiques polaires hydrophiles. Ainsi, le phtalate, légèrement polaire, présente une rétention réversible (Rd ~1,6 L.kg 1), majoritairement sur les phases argileuses. Le citrate, très polaire et fortement adsorbé (Rd ~ 40 L.kg-1), présente une hystérèse de désorption persistante et une affinité avec différentes phases de la roche (minéraux argileux et oxydes minoritaires). Enfin, l’acétate, l’adipate et le benzoate, peu polaires, présentent une affinité moindre avec la roche (Rd < 0,2 L.kg-1). Le comportement diffusif sur roche compacte de ces anions organiques a alors été étudié. Les valeurs de coefficient de diffusion effectif, De, et facteur de retard ont été quantifiées. La faible diffusivité, [De/D0]ANIONS ORGANIQUES ~ 0,1 à 0,25 × [De/D0]EAU, indique un effet d’exclusion anionique, de même intensité que celui observé pour les anions inorganiques. De plus, les coefficients d’adsorption, Kd, estimés à partir des retards à la diffusion sont environ 2 à 5 fois inférieurs aux coefficients de distribution Rd mesurés sur roche dispersée. Cette différence de comportement n’a pas pu être imputée, ni à des effets de cinétique, ni à des effets de porosité accessible aux anions. Quoiqu’il en soit, les espèces complexantes présentent un retard significatif à la diffusion (Kd > 0,2 L.kg-1), ce qui conforte les capacités de confinement de la roche vis-à-vis de ces espèces. / The Callovo-Oxfordian mudstone (COx) is studied as a possible host rock for a deep disposal of radioactive waste (Cigéo project). Indeed, besides being very weakly permeable, it presents a high content of clayey minerals, capable of retaining radionuclides under cationic form and to delay strongly their transport. Nevertheless, some waste packages may release a significant amount of organic molecules, capable of complexing these radionuclides and drastically increase their mobility. So, the objective of this work was to better understand the diffusive behavior of several organic molecules of interest in this mudstone, by investigating at first their affinity with the host rock. The retention of organic molecules under anionic form (acetate, phthalate, adipate, benzoate, and citrate) was quantified on to the dispersed COx mudstone using adsorption/desorption batch experiments. Experiments on decarbonated rock and clay fraction only (< 2µm) were also performed to identify solid phases and chemical functions responsible for the retention. A correlation of the intensity of retention, Rd, was pointed out whit the dipole moment µ(Orga.), providing a qualitative estimate of retention capacity for polar hydrophilic organic molecules. So, phthalate, slightly polar, displays a reversible retention (Rd ~1,6 L.kg-1), mainly on clayey phases. Citrate, very polar and strongly adsorbed (Rd ~ 40 L.kg 1), displays a persistent desorption hysteresis and an affinity to different solid phases (clayey minerals and minor oxides). Lastly, acetate, adipate and benzoate, weakly polar, display a lower affinity with rock (Rd < 0,2 L.kg-1). The diffusive behavior in compact rock of these organic anions was then studied. The effective diffusion coefficient and retardation factor values were quantified. The low diffusivity, [De/D0]ORGANIC ANIONS ~ 0,1 à 0,25 × [De/D0]WATER evidences an effect of anionic exclusion, with a same intensity as that observed for inorganic anions. Furthermore, the Kd adsorption coefficient, estimated from retarded diffusion are approximately 2 to 5 times lower than the Rd distribution coefficient measured on dispersed rock. This difference of behavior was not able to be attributed, or to kinetic effects, nor to accessible porosity to anions effects. Anyway, the complexing species display a significant diffusive retardation (Kd > 0,2 L.kg-1) consolidating the contain properties of the COx mudstone toward this species.

Interactions between plant roots and soil microorganisms in the rhizosphere are critical for plant growth. However, understanding of precisely how root exudates influence the diversity and activity of rhizosphere microorganisms is limited. The main objective of this study was to investigate the effect of radiata pine (Pinus radiata) root exudates on rhizosphere soil microbial communities, with an emphasis on the role of low molecular weight organic anions. The study involved the development and validation of new methods for investigating rhizosphere processes in a purpose-built facility. This included development of an in situ sampling technique using an anion exchange membrane strip to collect a range of organic anions exuded from radiata pine roots grown in large-scale rhizotrons. These included tartarate, quinate, formate, malate, malonate, shikimate, lactate, acetate, maleate, citrate, succinate and fumarate. Soil microbial activity and diversity were determined using dehydrogenase activity and denaturing gradient gel electrophoresis. Links between organic anions in root exudates and rhizosphere soil microbial community structures were investigated by comparing wild type and genetically modified radiata pine trees which were grown in rhizotrons for 10 months. As expected, there was considerable temporal and spatial variability in the amounts and composition of organic anions collected, and there were no consistent or significant differences determined between the two tree lines. Significant differences in rhizosphere microbial communities were detected between wild type and genetically modified pine trees; however, they were inconsistent throughout the experiment. The shifts in microbial communities could have been related to changes in exudate production and composition. Based on results from the main rhizotron experiment, a microcosm study was carried out to investigate the influence of selected pine root exudate sugars (glucose, sucrose and fructose) and organic anions (quinate, lactate and maleate) on soil microbial activity and diversity. Soil microbial activity increased up to 3-fold in all of the sugar and organic anion treatments compared to the control, except for a mixture of sugars and maleate where it decreased. The corresponding impacts on soil microbial diversity were assessed using denaturing gradient gel electrophoresis and 16S rRNA phylochips. Addition of the exudate compounds had a dramatic impact on the composition and diversity of the soil microbial community. A large number of bacterial taxa (88 to 1043) responded positively to the presence of exudate compounds, although some taxa (12 to 24) responded negatively. Organic anions had a greater impact on microbial communities than sugars, which indicated that they may have important roles in rhizosphere ecology of radiata pine. In addition, a diverse range of potentially beneficial bacterial taxa were detected in soil amended with organic anions, indicating specific regulation of rhizosphere microbial communities by root exudates. This project highlighted the considerable challenges and difficulties involved in detailed investigation of in situ rhizosphere processes. Nonetheless, the findings of this study represent a significant contribution to advancing understanding of relationships between root exudates and soil microbial diversity, which will be further enhanced by refinement and application of the specific methodologies and techniques developed.

Une caractéristique nutritionnelle peu connue des fromages est leur potentiel acidifiant, qui se révèle au cours du métabolisme et, à long terme, est susceptible d’induire des effets délétères sur la santé du consommateur. Malgré des conséquences physiopathologiques bien connues, très peu d’études se sont intéressées au potentiel acidifiant/alcalinisant des aliments et aucune à celui des fromages. L’objectif principal était d’évaluer d’une part le potentiel acidifiant des fromages et identifier ses déterminants au cours de la fabrication et d’autre part d’explorer des stratégies d’optimisation technologique permettant de réduire le potentiel acidifiant des fromages, tout en assurant leurs qualités gustatives. Le potentiel acidifiant a été évalué sur la base de l’indice PRAL (Potential Renal Acid Load, en tenant compte des teneurs en protéine, P, Cl, Na, K, Mg et Ca) et de la teneur en anions organiques (lactate et citrate). Dans un premier temps, l’étude du potentiel acidifiant de cinq types de fromages du commerce a permis d’établir un lien fort entre le type du fromage et son potentiel acidifiant. L’indice PRAL le plus faible est celui du fromage frais avec - 0,8 mEq/100 g, les indices les plus élevés atteignant 25,3 mEq/100 g pour le fromage à pâte pressée non-cuite (Cantal) et 28,0 mEq/100 g pour le fromage à pâte persillée (Fourme d’Ambert). Ce positionnement a ainsi permis de sélectionner un modèle fromage pour la suite des travaux : la Fourme d’Ambert. Dans une seconde phase, l’égouttage et le salage ont été identifiés comme les deux étapes technologiques déterminantes dans la génération du potentiel acidifiant du modèle fromage choisi, au cours de la transformation fromagère, suivie en milieu industriel. Ces études démontrent un déséquilibre important entre les éléments acidifiants (Cl, P, protéines) et les éléments alcalinisants majeurs (Na et Ca) du PRAL. En particulier, les Cl suivis par le P, ont exercé un très fort impact expliquant les indices élevés obtenus. Enfin, une substitution du NaCl par des sels organiques de calcium (lactate et citrate de Ca) a été testée en conditions industrielles pendant le salage à sec de la Fourme d’Ambert. Les deux sels ont montré un réel intérêt pour substituer partiellement le sel des fromages, sans affecter les propriétés sensorielles des produits finis et notamment les saveurs salée et amère. La substitution au lactate de Ca permettrait d’optimiser le potentiel acidifiant des fromages, en diminuant le PRAL et la teneur en Na et en augmentant la teneur en lactate. La substitution au citrate de Ca serait plutôt indiquée dans le cadre d’un enrichissement en Ca. En conclusion, ces études ont permis d’identifier les leviers à maîtriser pour réduire le potentiel acidifiant des fromages. L’approche adoptée a proposé la mise en application d’un concept connu principalement des nutritionnistes jusqu’ici dans les domaines de la biochimie et de la technologie alimentaires. Les perspectives d’innovation envisagées sont pertinentes avec les enjeux de santé publique actuels, en visant la réduction en Na dans les fromages et en participant à la limitation de l’acidose métabolique latente induite par les régimes occidentaux. Enfin, les retombées économiques de ces recherches sont prometteuses pour les filières fromagères. / A disregarded nutritional feature of cheeses is their acid-forming potential when ingested, associated with deleterious effects for consumers’ health. Despite the well-known pathophysiological consequences, very few studies investigated the acidifying/alkalizing potential of foods and especially, none targeted cheeses. The research project aimed on the one hand to evaluate the acid-forming potential of cheeses and identify the main key steps of the manufacture involved in this phenomenon and on the other hand to explore technological optimization strategies to reduce the acid-forming potential of cheeses, without altering their sensory properties. The acid-forming potential was evaluated on the basis of their Potential Renal Acid Load (PRAL) index (considering protein, P, Cl, Na, K, Mg and Ca contents) and organic anions contents (lactate and citrate). Firstly, the study of the acid-forming potential of five commercial cheeses from different cheese-making technologies established a strong link between the type of cheese and their acid-forming potential. PRAL index ranged from - 0.8 mEq/100 g for fresh cheese to 25.3 mEq/100 g for hard cheese (Cantal) and 28.0 mEq/100 g for the blue-veined cheese Fourme d’Ambert. This positioning allowed to select Fourme d'Ambert as model cheese for next steps. Secondly, draining and salting were identified as the main key steps responsible for the generation of the acid-forming potential of the model cheese, by following an industrial cheese-making process. These studies emphasized a great imbalance between acidifying elements of PRAL calculation (Cl, P and proteins elements) and alkalinizing ones (Na and Ca). Particularly, Cl followed by P elements had a strong impact on the PRAL value. Finally, the salt substitution with organic calcium salts (calcium lactate and calcium citrate) was tested under industrial conditions during the dry salting of Fourme d'Ambert cheese. Both salts showed a real nutritional interest to partially replace salt in cheese, without affecting their sensory properties and especially the salty and the bitter flavors. The salt substitution by calcium lactate could reduce the acid-forming potential of cheeses, by decreasing the PRAL and the sodium content and by increasing the lactate content. The calcium citrate substitution would rather be recommended for Ca enrichment of cheeses. As a conclusion, these studies allowed to identify technological solutions to reduce the acid-forming potential of cheeses. The adopted approach proposed the implementation of a concept, known mainly by nutritionists so far, to the biochemistry and the food technology fields. The considered prospects for innovation are relevant with the current public health issues, targeting the reduction of Na in cheeses and participating in the limitation of the Western diets induced metabolic acidosis. Finally, the economic benefits of this research are promising for cheese-making producers.