Résumé
Plants interact closely with arbuscular mycorrhizal (AM) fungi. They allocate photosynthates to AM fungi in exchange for nutrients, thereby influencing plant fitness. Although plant phenotypes result from multiple traits constrained by trade-offs, the effects of AM fungi on plants are often studied using one trait. Plant response to AM fungi therefore needs to be analysed using multiple traits. Four Asteraceae species were inoculated with ten AM fungal strains using a factorial design in the greenhouse. The effect of AM fungal inoculation and their taxonomic identity on plants vegetative and reproductive traits were assessed. The predictability of the effects was evaluated based on AM fungal phylogenetic relatedness. The effect of the inoculation depended on the trait considered. Compared with the non-inoculated control, biomass allocation to roots decreased, while allocations to shoots or reproduction increased depending on the AM fungi or the plant. Significant differences were observed among AM fungi inoculates used, whether looking at separate traits, trade-offs between vegetative or reproductive growth, and the trait syndrome. In Centaurea cyanus, changes in plant phenotype were associated with the phylogenetic distance between AM fungi. These results underline the importance of using multi-trait approaches to understand AM fungal effects on plant phenotype. In accordance with the holobiont concept, the outcomes of this interaction depended on both the host plant and the AM fungus involved. It contributes to a better understanding of the biological effectors shaping the reaction norm (i.e., the range of phenotypic variation of a given host genotype) within the plant holobiont.