Arbuscular mycorrhizal inoculation and plant response strongly shape bacterial and eukaryotic soil community trajectories

Arbuscular mycorrhizal (AM) fungi and terrestrial plants form one of the most important and ubiquitous symbioses on the planet. Although the central role of AM fungi in rhizosphere processes is well established, the extent of their influence on the development of the whole soil microbial community is less well characterized. We assessed the temporal dynamics of the bacterial and eukaryotic soil microbial communities in mesocosms where AM fungi were inoculated on a grass (Holcus lanatus L.) and a clover (Trifolium pratense L.). This allowed us to evaluate whether 1) inoculation with AM fungi changes the overall structure of soil communities and 2) if these changes are partially mediated by the altered plant phenotype, as indicated by increases in growth and photosynthetic activity. We observed changes in the community composition of both microbial groups, largely associated with relative decreases in Proteobacteria, Nematoda and some protistan groups (Ciliophora and Lobosa) and relative increases in Gastrotricha and Firmicutes. Plant productivity doubled with mycorrhizal inoculation, while other plant performance measures increased by 10–50%. We conclude that the interaction between AM fungi and plants shapes the surrounding soil microbial communities, probably because enhanced growth of host plants changes the amount, timing, and form of carbon inputs into soil.