Root endophytic fungi show low levels of interspecific competition in planta

Roots are associated with fungal communities that affect plant growth and health. Individual root-associated fungi have different effects on plant performance, from detrimental to beneficial, but it is barely known how their inter-species interactions determine plant fitness. Here, we evaluate in planta interactions among dominant root-colonizing fungi with different degrees of phylogenetic and trait similarity, and the impact of their co-occurrence on their respective ability to colonize roots and their effects on plant growth. An in vitro bioassay with Arabidopsis thaliana as host plant was used for the co-cultivation with individual or paired combinations of fungal strains. Root colonization by strains was monitored using real-time quantitative PCR, and the effects on their host's growth were estimated by measuring plant biomass. Strains had variable effects on plant growth, although these effects were mostly modest and little affected by the presence of other fungi. Abundance of each fungus in roots responded differently to co-inoculation, but competition between strains was not associated with their similarity in functional traits. Our findings show little competition between dominant fungal root endophytes, which suggests that they occupy complementary root niches and could explain the high fungal diversity colonizing healthy hosts in natural conditions. (C) 2019 Elsevier Ltd and British Mycological Society. All rights reserved.