Study of arbuscular mycorrhizal fungi under hydrocarbon-polluted conditions and diversity associated to plants communities naturally recolonizing oil ponds in the Amazonian areas

Oil exploitation and its mishandling have left numerous polluted environments all over the world. The impact of oil on flora and fauna is perceptible in natural as well as anthropogenic environments and has resulted in the emergence of human diseases. In the Amazon basin of Ecuador, around 2550 oil-polluted sites have been identified and the government, supported by the public enterprise PetroAmazonas EP, has become responsible for the recovery of the hydrocarbon-polluted soils. Physical and chemical approaches are the more common methods used to remediate polluted soils, while the use of biological methods has increasingly attracted the attention of scientists, industrials and policy makers. Among the most promising methods is the phytoremediation assisted by arbuscular mycorrhizal fungi (AMF). AMF are obligate root symbionts that improve the nutrition of plants (particularly P) and increase their resistance/tolerance to abiotic (e.g. hydrocarbon-pollutants) stresses. Nowadays, their community composition in hydrocarbon-polluted soils as well as the impacts of hydrocarbon-pollutants on AMF physiology is poorly known. In this context, the first objective of the thesis was to study the AMF community composition in weathered crude oil ponds and surrounding soils naturally recolonized by native plants. High levels of root colonization were measured and the presence of four AMF families (i.e. Acaulosporaceae, Glomeraceae Archaeosporacea and Paraglomeraceae) and several species were detected by the Sanger sequencing and NGS pyrosequencing methods. This suggested the tolerance of AMF to hydrocarbon pollutants and their potential to help plants establishing and remaining in the polluted soils. These observations opened the door to our second objective which was to determine the role of the standard AMF R. irregularis MUCL 41833 on the uptake and transport of Pi to maize plantlets in presence of diesel. No significant effect of AMF was observed on Pi uptake and growth of the maize plantlets. Conversely, a detrimental effect of diesel was noticed both on plant growth and on fungus root colonization. Thus, it was assumed that this specific fungus was not adequate for phytoremediation, which does not exclude that other AMF (e.g. those from the oil-polluted soils) could improve plant tolerance to diesel and improve Pi uptake. Finally, in a third objective, we investigated the impact of diesel on an essential attribute of AMF to recover integrity following physical injury; i.e. the hyphae healing mechanism (HHM). This mechanism was monitored in two AMF species differing in their life history strategies, R. irregularis MUCL 41833 (an r- strategist) and Gigaspora sp. MUCL 52331 (a K-strategist). Both fungi differed in their ability to heal under increasing concentrations of diesel. In Gigaspora sp., the HHM was the most efficient way to maintain the viability of hyphae under adverse conditions, while in R. irregularis, this mechanism was of more limited importance, the fungus being able to reconnect injured hyphae only at low frequencies, probably investing more energy in connecting neighboring hyphae or roots as reported previously in absence of pollutants.