Combining ecophysiological and microbial ecological approaches to assess the interaction between Medicago truncatula genotypes and the soil microbial communities

To assess how plant and microbes genotypes may interfere, the genetic structure and diversity of microbial communities in the rhizosphere of different Medicago truncatula genotypes were studied in relation to the plant carbon (C) and nitrogen (N) nutrition at the whole plant level. For this purpose, the genetic structure of both rhizosphere bacterial and fungal communities was first analysed by Automated Ribosomial Intergenic Spacer Analysis (ARISA). Then, the C and N nutrition of the plant was estimated using a phenotypic description, a C and N isotope labelling and an ecophysiological framework. Finally, the results of these two approaches were compared using a coinertia analyse. An early effect of the plant genotype was observed on the bacterial communities, while few significant differences were detected at the plant phenotypic level. However, at a functional level, the different Medicago truncatula genotypes could be distinguished by their different nutritional strategies. Moreover, the coinertia analysis revealed that the microbiological and the ecophysiological approaches were correlated. The exploration of the genetic structure of microbial communities, when combined with an ecophysiological approach is an innovative way to progress in our knowledge of plant - microbial interaction in the rhizosphere.