The microbiota can play major roles mediating host adaptation. Plants rely on the ancestral Arbuscular Mycorrhizal (AM) symbiosis to supplement their phosphorus nutrition. However, recent findings indicate that the AM symbiosis is not essential. Indeed, there are at least three ‘non-mycorrhizal’ plant families for which the loss of the AM symbiosis was not compensated by any major nutritional innovation that we know of. Certain non-mycorrhizal Brassicaceae were discovered to associate with new types of root endophytic fungi capable of transferring phosphorus to the plant, suggesting the existence of yet-unknown nutritional associations between non-mycorrhizal plants and their microbiota. This project aims to uncover and describe these associations by developing a novel approach to follow phosphorus in rhizosphere microbial communities. We hypothesize that non-mycorrhizal plants adapted to the loss of the AM symbiosis by establishing new nutritional microbial partnerships promoting their phosphorus nutrition.