Les objectifs de cette thèse étaient (i) d'étudier les mécanismes par lesquels les nématodes bactérivores régulent les flux de nutriments (N et P) dans la rhizosphère du riz pluvial dans un sol ferrallitique de Madagascar, (ii) d'étudier les effets des interactions bactéries – bactérivores sur les fonctions de la plante (croissance et nutrition), et (iii) d'évaluer les principaux facteurs contrôlant la boucle microbienne des sols dans une optique d'intensification. Notre modèle biologique comprenait Acrobeloides sp. (Cephalobidae) et Oryza sativa (Poaceae).Deux voies ont été proposées pour expliquer les effets positifs des bactérivores sur la disponibilité des nutriments et les fonctions de la plante: voie de minéralisation et voie d'exploration. Afin d'identifier l'implication de chaque voie dans les flux de P inorganique à l'interface sol-plante nous avons utilisé le radio-isotope 32P comme traceur. Lorsque le pH du sol est corrigé par l'ajout de dolomie, la présence des nématodes bactérivores améliore la minéralisation nette de P, la production de biomasse et la nutrition de la plante sans modifier la ramification du système racinaire, contrairement à ce qui a été observé par certains auteurs en présence de protistes. En effet, en présence de nématodes et de dolomie, la L-value dans les parties aériennes de la plante augmente de 49%, la biomasse totale de la plante augmente de 22%, et la quantité de P total dans les tissus de la plante augmente de 9%. Ainsi, Acrobeloides sp. stimule le prélèvement de P par la plante via la voie nutritionnelle ou voie de minéralisation.Les effets de Acrobeloides sp. sur les fonctions de la plante sont variables (positives, neutres, négatives), en fonction des pratiques agricoles et des caractéristiques abiotiques du sol. Tout d'abord, ces effets peuvent dépendre de la variété de riz puisque l'attractivité des nématodes Acrobeloides sp. par la rhizosphère du riz varie en fonction des variétés de riz pluvial, plus précisément en fonction de la composition et de la quantité d'exsudats racinaires libérés par la plante. Ensuite, l'activité mutualiste des nématodes est influencée (maximisée) par la présence d'arbres (agroforesterie) dans la parcelle de riz pluvial. En plus des plantes, les paramètres édaphiques étaient des facteurs clés. L'activité mutualiste des nématodes est fortement limitée par le pouvoir fixateur des Ferralsols. Ainsi, l'ajout de dolomie limite la capacité de sorption de P du sol et améliore l'activité mutualiste des nématodes bactérivores. Enfin, l'activité mutualiste des nématodes sur la croissance et la nutrition du riz pluvial est favorisée par les valeurs élevées de pH et de teneur en Mg dans le sol. Pour conclure nous avons trouvé qu'il est possible d'intensifier l'activité mutualiste des nématodes bactérivores dans un sol tropical pauvre à travers des pratiques agricoles spécifiques (gestion des sols, agroforesterie). / Using Acrobeloides sp. (Cephalobidae) and Oryza sativa (Poaceae), we aimed at (i) studying the effects of bacterivorous nematodes on plant functions growing in a nutrient-poor soil in Madagascar, (ii) testing the mechanisms involved in the mutualistic activity of the bacterivorous nematodes in a strong P-depleted Ferralsol from the highlands of Madagascar, and (iii) identifying the agronomic and edaphic factors that can drive the soil microbial loop.Two pathways have been proposed to explain the positive effects of bacterial-feeders on nutrients availability and plant functions: mineralization pathway and exploration pathway. In order to test the involvement of each pathway in the mutualistic activity of bacterivorous nematodes, we assessed the effect of nematodes inoculation on inorganic P flows from soil to plant using the 32P labelling technique. When the soil pH was corrected with dolomite lime, we showed that the presence of Acrobeloides sp. improved net P mineralization and plant (Oryza sativa) functions (growth and nutrition) but did not alter lateral root growth as protists do. Indeed, in the presence of nematodes and dolomite, the shoot L-value increased by 49%, the plant total biomass increased by 22% and the plant total P amount increased by 9%. Thus, Acrobeloides sp. increased plant P uptake through the "nutritional" or "mineralization" pathway.The effects of Acrobeloides sp. on Oryza sativa functions were variable (positive, neutral or negative) according to agricultural practices and soil abiotic variables. First, these effects may depend on the rice cultivar used in the experiment. Indeed, the nematodes attractancy to root-adhering soils varied according to upland rice cultivar, probably according to the amount and composition of root exudates. The mutualistic activity of nematodes is also influenced (maximized) by the presence of trees (agroforestry) in the rice field. Besides plants, the abiotic soil parameters were key drivers. The mutualistic activity of nematodes was strongly limited by the ability of Ferralsols to precipitate and chemisorb phosphates. The addition of dolomite lime limited phosphates sorption on soil and enhanced the mutualistic activity of the nematodes. Also, the high values of soil pH and Mg content tended to increase the mutualistic activity of the bacterivorous nematodes on rice growth and nutrition. To conclude, we found that it is possible to drive the mutualistic activity of bacterivorous nematodes in poor tropical soils through specific soil and agricultural practices.

Made available in DSpace on 2014-06-11T19:30:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-04-10Bitstream added on 2014-06-13T20:20:57Z : No. of bitstreams: 1 mauad_m_dr_botfca.pdf: 831349 bytes, checksum: fd4013d6c11ec26447104ebab569ba3e (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O cultivo de arroz de terras altas sob condições de sequeiro é considerado um cultivo de risco, sendo a água o fator ambiental mais ligado à baixa produtividade. A identificação e a compreensão dos mecanismos de tolerância à seca, bem como o desenvolvimento de práticas culturais que aumentem essa tolerância são fundamentais para alcançar maior estabilidade na produção. A adubação silicatada tem aumentado a tolerância das plantas aos estresses biótico e abiótico. O trabalho teve como objetivo avaliar o desenvolvimento de cultivares de arroz de terras altas sob condição de déficit hídrico e adubação silicatada e a marcha de absorção e acúmulo de silício na parte aérea. Foram instalados dois experimentos em casa de vegetação, o primeiro foi delineado em blocos ao acaso em esquema fatorial 2 x 2 x 2 com quatro repetições. Os tratamentos foram constituídos por duas cultivares (Caiapó - tradicional e Maravilha - moderno), em duas tensões de água no solo (-0,025 MPa e -0,050 MPa) e duas doses de silício ( 0 e 350 kg ha-1Si). O segundo experimento foi conduzido de maneira inteiramente casualizado em esquema fatorial 2 x 2 x 7 com quatro repetições, sendo duas cultivares (Caiapó e Maravilha) dois corretivo de solo (carbonato de cálcio e silicato de cálcio) e sete estádios de desenvolvimento (início do perfilhamento, perfilhamento máximo, diferenciação do primórdio da panícula, emborrachamento, antese, grão leitoso e maturação fisiológica.) O estresse hídrico reduziu o 2 número de panícula por metro quadrado, o número total de espiguetas por panícula, a fertilidade das espiguetas e, consequentemente, a produtividade de grãos. Sob condições de estresse hídrico, o silício reduz o teor de prolina na fase vegetativa e reprodutiva e aumenta a atividade da peroxidase na fase reprodutiva, podendo ser um indicativo de tolerância a esse estresse. As cultivares de arroz acumulam silício em quantidades. / The highland rice cultivate under upland condition is considered a risk cultivate, being the water enviroment factor most linked to low productivity. The identification and the understanding of the dry tolerance mechanisms as well as the development of culture practical that increase this tolerance are fundamental to achieve more stabitity, productivity on highland rice cultivate specially on upland system. The silicon fertilization have been increased the plants tolerance under biotic and abiotic stress. This silicon fertilization have been increased the plants tolerance to biotic and abiotic stress. This research had the objective to evaluate the development of the upland rice cultivar under water stress condition and silicon fertilization and uptake dynamic of silicon in the aerial part of the plant. The were installed two experiment in greenhouse, the first experiment was outlined at random blocks design in a factorial draft 2x2x2 with four replication. The treatments were 4 two cultivars ( Caiapó- Traditional and Maravilha Modern) for two tension of water on the ground ( -0,025 MPa e -0,0050 MPa) and for two silicon rates ( 0 and 350 kg ha-1Si). The second experiment was carried out as entirely randomized design factorial draft 2x2x7 with four replication, being two cultivares (Caiapó and Maravilha) two soil amendments (limestone and calcium silicate) and seven estage of development. The water stress decreased the number of panicle per square meter, the total number of spikets per panicle, spiketel fertility and consequently the grains productivity. Under water stress, the silicon decrease the proline level at vegetation and reproductive stage and increase the peroxide activity at reproductive stage, could be a tolerance indicative to this stress. The rice cultivares accumulate silicon in different quantity. The silicon uptake dynamic and silicon accumulate is gradual at the Caiapó cultivar, since the tillering to the booting, while.

Resumo: O cultivo de arroz de terras altas sob condições de sequeiro é considerado um cultivo de risco, sendo a água o fator ambiental mais ligado à baixa produtividade. A identificação e a compreensão dos mecanismos de tolerância à seca, bem como o desenvolvimento de práticas culturais que aumentem essa tolerância são fundamentais para alcançar maior estabilidade na produção. A adubação silicatada tem aumentado a tolerância das plantas aos estresses biótico e abiótico. O trabalho teve como objetivo avaliar o desenvolvimento de cultivares de arroz de terras altas sob condição de déficit hídrico e adubação silicatada e a marcha de absorção e acúmulo de silício na parte aérea. Foram instalados dois experimentos em casa de vegetação, o primeiro foi delineado em blocos ao acaso em esquema fatorial 2 x 2 x 2 com quatro repetições. Os tratamentos foram constituídos por duas cultivares (Caiapó - tradicional e Maravilha - moderno), em duas tensões de água no solo (-0,025 MPa e -0,050 MPa) e duas doses de silício ( 0 e 350 kg ha-1Si). O segundo experimento foi conduzido de maneira inteiramente casualizado em esquema fatorial 2 x 2 x 7 com quatro repetições, sendo duas cultivares (Caiapó e Maravilha) dois corretivo de solo (carbonato de cálcio e silicato de cálcio) e sete estádios de desenvolvimento (início do perfilhamento, perfilhamento máximo, diferenciação do primórdio da panícula, emborrachamento, antese, grão leitoso e maturação fisiológica.) O estresse hídrico reduziu o 2 número de panícula por metro quadrado, o número total de espiguetas por panícula, a fertilidade das espiguetas e, consequentemente, a produtividade de grãos. Sob condições de estresse hídrico, o silício reduz o teor de prolina na fase vegetativa e reprodutiva e aumenta a atividade da peroxidase na fase reprodutiva, podendo ser um indicativo de tolerância a esse estresse. As cultivares de arroz acumulam silício em quantidades. / Abstract: The highland rice cultivate under upland condition is considered a risk cultivate, being the water enviroment factor most linked to low productivity. The identification and the understanding of the dry tolerance mechanisms as well as the development of culture practical that increase this tolerance are fundamental to achieve more stabitity, productivity on highland rice cultivate specially on upland system. The silicon fertilization have been increased the plants tolerance under biotic and abiotic stress. This silicon fertilization have been increased the plants tolerance to biotic and abiotic stress. This research had the objective to evaluate the development of the upland rice cultivar under water stress condition and silicon fertilization and uptake dynamic of silicon in the aerial part of the plant. The were installed two experiment in greenhouse, the first experiment was outlined at random blocks design in a factorial draft 2x2x2 with four replication. The treatments were 4 two cultivars ( Caiapó- Traditional and Maravilha Modern) for two tension of water on the ground ( -0,025 MPa e -0,0050 MPa) and for two silicon rates ( 0 and 350 kg ha-1Si). The second experiment was carried out as entirely randomized design factorial draft 2x2x7 with four replication, being two cultivares (Caiapó and Maravilha) two soil amendments (limestone and calcium silicate) and seven estage of development. The water stress decreased the number of panicle per square meter, the total number of spikets per panicle, spiketel fertility and consequently the grains productivity. Under water stress, the silicon decrease the proline level at vegetation and reproductive stage and increase the peroxide activity at reproductive stage, could be a tolerance indicative to this stress. The rice cultivares accumulate silicon in different quantity. The silicon uptake dynamic and silicon accumulate is gradual at the Caiapó cultivar, since the tillering to the booting, while. / Orientador: Hélio Grassi Filho / Coorientador: Carlos Alexandre Costa Crusciol / Banca: Orivaldo Arf / Banca: Sonia Regina de Souza / Banca: Gaspar Henrique Korndorfer / Banca: José Salvador Simonetti Foloni / Doutor