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The thesis focused on the response of the rhizobial-mycorrhizal-lentil symbiosis to arsenic as an environmental contaminant. This was instigated by the concern over the arsenic contaminated irrigation water problem in South East Asia, and in particularly, its impact on Bangladesh agriculture. This led to a holistic approach to the study, by investigating the effect of inoculation with Rhizobium leguminosarum and the AM fungus Glomus mosseae, as well as application of superphosphate and rock phosphate, on lentil growth, nitrogenase activity and nutrient uptake (especially N and P) in the presence of arsenic contaminated irrigation water. Positive effects of mycorrhizal inoculation on lentil (Lens culinaris L.) growth, nitrogen fixation and P nutrition were observed, along with reduced uptake of As in roots, shoots and pods. Decreased plant growth, nitrogen fixation, nutrient uptake, mycorrhizal infection and increased uptake of arsenic in root, shoot and pods were observed due to application of arsenate contaminated irrigation water. The use of a lux based bacterial biosensor test demonstrated that mycorrhizal inoculation reduced arsenic bioavailability in soil and that most of the toxicity was associated with the colloidal and fine particulate soil fraction. When rock phosphate was applied, an increase of P uptake only was observed. In contrast, superphosphate increased both P and As uptake and decreased mycorrhizal infection and activity. In summary, this thesis has shown that mycorrhizal inoculation appears to offer great potential as an effective tool contributing to crop management for technique in minimisation of the total intake of As by human and livestock. The observed decreased in uptake of As into pods of mycorrhizal lentil has particularly important potential implications for human health.

Although air pollution levels are increasing, there is no knowledge of air pollution effects on agricultural crops in the Peshawar region of Pakistan. The aim of this study was to assess the impact of ozone (O3) and hydrogen fluoride (HF) on agricultural crops in Peshawar through a combination of field work and experiments. The mean monthly O3 concentration in Peshawar, measured using passive samplers, was between 25-30ppb in February and March, but increased to 35-55ppb in April and May; it fell to 15-20ppb in November/December. O3 injury was found on potato (black flecking), onion (leaf tipburn) and cotton (white stipples) in a survey in April/May, but was absent from many other crops. No O3 injury was found on any crops during a winter survey. O3 fumigation experiments on spinach (Beta vulgaris) and onion (Allium cepa) in open-top chambers in UK showed that high O3 concentrations can affect both species in terms of visible injury and growth. However, onion is at greater risk in the field as it is a summer crop and is likely to be exposed to high O3 concentrations, unlike spinach, which is grown in the winter season. An EDU experiment on spinach under field conditions in Peshawar showed no effect on growth during winter season. However, elemental contents of spinach were significantly reduced in EDU treated plants. The HF concentrations in Peshawar, measured using passive samplers were higher in summer than in winter in areas close to brick kiln fields. The mean summer concentration was 0.2μg HF m-3, with maximum of 0.3μg HF m-3 in May. HF was below detection limits of <0.1μg HF m-3 in November-December. Severe HF injuries to mango, apricot and plum leaves, in form of necrotic leaf margins and tipburn, were found near the brick kiln fields. Tomato, maize, wheat and sugarcane were found to be less sensitive, but also showed some HF injury. The fluoride content of fruit leaves, wheat grains and spinach was significantly higher in the brick kiln area than at control sites. There was no significant difference between the soil fluoride content of wheat fields in the brick kiln area and at control sites. Wheat grown at different NaF levels in alkaline soils similar to those in Peshawar, in a greenhouse experiment in the UK showed no effect of fluoride on growth. The degree of powdery mildew infestation increased with increased fluoride concentrations in the soil and ear emergence was also delayed in all treatments except the control. It was concluded that O3 and HF are significant pollutants in Peshawar, especially for summer crops. More detailed studies should be conducted to determine the magnitude of damage caused by these pollutants in the Peshawar region.

En France et en Europe, la fin des activités industrielles liées à l’exploitation du charbon a laissé de nombreux sites et sols pollués par les hydrocarbures aromatiques polycycliques (HAP). La rhizodégradation pourrait permettre leur dépollution par l’utilisation de plantes et de leur microflore associée. Toutefois, l’efficacité de cette technique, démontrée en conditions contrôlées de laboratoire, est limitée in situ par de fortes mortalités ou l’inhibition de croissance de la plante. De plus, le transfert de ces polluants dans la plante peut menacer la chaîne alimentaire. Ce travail se propose d’étudier les interactions entre le maïs, choisi ici comme plante modèle, et les HAP de sols industriels contaminés ou un de leur représentant, le phénanthrène ajouté à un substrat simplifié. Le prélèvement des HAP et leur effet sur la physiologie de la plante sont évalués sur des systèmes de complexité croissante et en abordant ces questions à différentes échelles, allant de la cellule à la plante entière. Il s’agit en particulier d’élucider les mécanismes de transfert et de translocation des HAP dans la plante et d’identifier les réponses toxiques de celle-ci. Les résultats mènent à l’hypothèse d’une sorption physique des HAP de la phase solide du sol par contact direct avec les racines comme mécanisme principal d’entrée et non par transport dans la phase aqueuse. Les principaux arguments sont les distributions moléculaires similaires entre les HAP totaux dans les terres et celles dans les racines, les mauvaises corrélations entre les concentrations en HAP dissous dans l’eau porale et les racines, ainsi que la surestimation des concentrations prédites par des modèles existants fondés sur un prélèvement de la solution du sol. La localisation du PHE dans les racines à l’aide d’outils de microscopie montre une subérification précoce de l’exoderme et l’endoderme, même à de faibles teneurs (50 mg kg-1). Le prélèvement de nutriment ne semble pas affecté mais d’importantes accumulations et carences d’éléments sont observées dans les parties aériennes. Ces perturbations nutritionnelles du maïs pourraient affecter le fonctionnement de la plante et par conséquent limiter sa croissance ou entraîner sa mort / In Europe and France, the end of industrial activities associated to coal exploitation left numerous wastelands contaminated with polycyclic aromatic hydrocarbons (PAH). Rhizodegradation enables their remediation by using plants associated with microflora. However, the efficiency of this technique, demonstrated at the laboratory scale, is often limited in situ by high plant mortality or inhibited growth. Furthermore, the PAH uptake in plants may threaten the food chain. This work studied the interactions between maize, chosen as model plant, and PAH from industrial contaminated soils or from simplified model systems, i.e. sand spiked with phenanthrene. PAH uptake and their effect on the plant physiology were assessed using systems of increasing complexity, to solve questions raised at different scales, from the cell to the whole plant. Mechanisms involved in PAH uptake and translocation are proposed and the toxic responses of the plant are detailed. Results lead to a new hypothesis: PAH from the solid phase penetrate the roots by physical and direct contact and not only through uptake in pore water. Main arguments are: similar molecular distributions in soils and roots, low correlations between PAH concentrations in pore water and roots and overprediction of bioaccumulation by using predicting models based on root absorption in soil solution. Localization of PHE in roots using microscopic tools showed early suberisation of endoderm and exoderm in presence of PHE, even at low concentration (50 mg kg-1). Nutrient uptake seemed not affected but large elements accumulations and depletion were observed in aerial part of maize. These nutritional disruptions may affect plant functioning and consequently, decrease its growth or even cause its death