Steering root microbiomes of a commercial horticultural crop with plant-soil feedbacks

Plant-soil feedbacks (PSFs) can influence plant performance in natural and agricultural systems but how PSF principles can be applied in agriculture is not well-studied. In a two-phase PSF experiment, we tested how inoculating soil conditioned by plants into live and sterilized commercial glasshouse soil influences the root-associated microbiome (bacteria and fungi) and biomass of the cut flower chrysanthemum. The conditioned soil inocula were obtained by growing eight grassland species and chrysanthemum individually in soil collected from a commercial chrysanthemum glasshouse, or in soil from a natural grassland. Inoculation of conditioned grassland soil into sterilized glasshouse soil led to higher plant biomass, to more complex and connected microbial networks and to a lower abundance of the pathogenic fungi Olpidium in chrysanthemum roots, than inoculation into live glasshouse soil or inoculation with conditioned live glasshouse soil. Biomass of chrysanthemum was highest in 100% sterilized soil, but in this soil the root-associated microbiome also contained the highest relative abundance of Olpidium. Glasshouse soils are frequently swam-sterilized and our results show that inoculating these soils with desired soil microbiomes can steer the root microbiome in this crop. However, our study also highlights that steering live glasshouse soil with a disease-related microbiome into a healthy state remains challenging.