Drought is probably one of the biggest single threat from climate change which impacts are global, threatening particularly crop production. There is an urge in implementing sustainable agricultural practices in order to maintain/optimize crop production under drought conditions. AM fungi are soil microorganisms that establish symbiosis with more than 70% of land plants and whose role in mitigating the effects of drought on plants has been demonstrated in numerous studies. Optimization of plant-AM fungal association requires deeper investigation on the impact of decreasing water availabilities on these soil microorganisms and better knowledge on the role of these root symbionts in adaptation of plants to drought. In this thesis, we first investigated the effects of decreasing water availability on the life cycle, and on Pi uptake and transport capacity of AM fungi under strict in vitro culture conditions. Polyethylene glycol was used to decrease the water potential (reflecting water availability) of the growth medium. Germination and germ tube length of various AM fungal strains were affected differently and spores production, hyphal development and Pi uptake of the extraradical mycelium of the model fungus R. irregularis MUCL 41833 were impacted. Secondly, we evaluated if R. irregularis MUCL 41833 could still benefit plant despite an impact of decreased water availability on its biology. The effects of the fungus on Pi mobilization and leaf gas exchange parameters of maize plants grown in a semi-hydroponic cultivation system was assessed during recovery from drought. During recovery, the mycorrhizal plants took up Pi faster than the non-mycorrhizal ones, although both plants had similar root biomass and unrestricted access to Pi. The AM fungus also improved the instantaneous water use efficiency through a decrease of transpiration during recovery, possibly resulting in faster rehydration of the plants. In conclusion, AM fungi may behave differently under drought stress conditions, requiring a screening procedure to select the more resistant/tolerant and potentially efficient strain to mitigate water stress in plants. Despite an impact on their biology, AM fungi are still able to improve plant growth and nutrition parameters in particular, by inducing specific adaptation of plants during recovery. This result pleads for further investigations in the mechanisms involved in the recovery of AM-colonized plants to drought.