Soil microbial diversity importance for plant performance depends on symbiotic interactions

Soil microorganisms play a major role in ecosystem functioning through their trophic exchanges with plants. However, the role of the whole soil microbial diversity for primary production remains controversial, and its impact on microbe-plant symbiotic interactions remains unexplored. Soil microbial diversity was manipulated by inoculating a sterilized soil with serial dilutions of a microbial suspension issued from the same non-sterilized soil. We aimed to determine the consequences of microbial diversity erosion on growth and fitness of three plant model species with decreasing degree of symbiotic dependence: Medicago truncatula, Brachypodium distachyon and Arabidopsis thaliana. Decreasing the surrounding microbial diversity negatively affected symbiotic interactions while it differentially affected plant performance depending on plant-symbionts reliance. M. truncatula, B. distachyon and A. thaliana were negatively, positively and not significantly affected by erosion, respectively. These results are of interest to predict the consequences of soil microbial diversity erosion on crop plants according to their symbiotic interactions.