Improved establishment of Miscanthus x giganteus stem propagation by Herbaspirillum inoculation

The costly field establishment of the sterile perennial Miscanthus x giganteus from rhizomes is a severe constraint for expanding the production area of this highly nutrient efficient biomass crop. The bacterial endophyte Herbaspirillum frisingense GSF3O(T) isolated from temperate grasses has the potential to improve Miscanthus sinensis seedling growth when established from seeds. Here we found that stem cutting inoculation improved the shoot sprouting and establishment success of Miscanthus x giganteus in the greenhouse. In a small field trial, plant height and biomass from inoculated sites were significantly larger in the second year after establishment, but already after one year after inoculation, the bulk soil, rhizosphere, root and rhizome microbiomes were almost devoid of the beta-proteobacterium Herbaspirillum. While previous inoculation had little effect on the longterm bulk soil, rhizosphere and root microbiomes, the rhizome microbiome was massively reduced in diversity. In the rhizome, several proteobacteria, which are associated with plant growth promoting functions, were favored by inoculation. Our study suggests that H. frisingense inoculation may improve establishment of Miscanthus stem cuttings, appears to colonize the shoot and has long-lasting effects on the rhizome microbiome diversity, despite low rhizocompetence and low root abundance.