Plant neighbours shape fungi assemblages associated to roots in focal plants at early growth stage

Mony, Cendrine; Gaudu, Valentin; Ricono, Claire; Jambon, Olivier; Vandenkoornhuyse, Philippe

Growth chamber experiment testing the influence of different plant neighbourhoods of M. truncatula on its fungal microbiota
Growth chamber experiment testing the influence of different plant neighbourhoods of M. truncatula on its fungal microbiota

Arbuscular mycorrhizal fungi (AMF), microorganisms associated with plant roots, significantly affect plant nutrition and health. Empirical and experimental records show a certain degree of host-preference in plant-AMF interactions, leading to particular AMF assemblages associated with different species. But in the real world, a plant is not alone but generally coexists with others. Here we test the idea that AMF assemblages depend on the type of neighbours a plant grows with, because they may influence the pool of AMF species that can be recruited by the plant. Furthermore, we expect that some of the characteristics of the neighbour plant, in terms of evolutionary history (phylogeny) or biology (functional traits), may play a part in the recruitment process of AMF by the plant and/or the probability of dispersal of AMF between plants, and could hence explain the resulting AMF-plant associations.

We tested these predictions on the focal plant Medicago truncatula. We focused on the early stage of plant growth as mycorrhizas may stimulate the early development of a plant when it arrives within a plant community. We set up an experiment testing the effect of 15 neighbour plants on M. truncatula. They were selected from five taxonomic families.

We demonstrated that neighbour plants influenced the composition and richness of AMF assemblages associated with the focal plant. Neighbour species belonging to some of the taxonomic families tested (Brassicaceae, Poaceae), led to absent or less diverse AMF assemblages, while others (Rosaceae, Asteraceae) contributed to a higher diversity of AMF assemblages associated with the focal plant roots. We were not able to predict these effects through the evolutionary history of the neighbouring plant, but by plant traits, especially those related to nutrient uptake and use. AMF assemblages were both enriched and more similar between focal and neighbour plants when the focal and neighbour plants differed more in their root traits.

This study shows that neighbour plants influence the microbiota of a plant when it arrives in a community. This suggests that the way plants are arranged in space, because of this influence on microbial assemblages, could have an effect on plant coexistence.

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