Plant genotype influences the structure of the Miscanthus-associated microbiome

Background/Question/Methods

Sustainability is a key economic and environmental issue in agricultural systems, but it is particularly critical for bioenergy feedstock production. Reducing anthropogenic N inputs and optimizing benefits derived from the plant-associated microbiome may improve the energetic and economic viability of bioenergy crops. Modeling and ¹⁵N dilution experiments indicate that diazotrophs associated with Miscanthus (a potential biofuel crop) can contribute significant amounts of nitrogen to plant growth and sustainability Our ability to derive benefit from these mutualisms, however, is limited by our lack of understanding about ecological drivers that govern microbial abundance and activity in grasses. We hypothesize that the plant microbiome is influenced by plant genotype, and in particular, that the ability to recruit diazotrophs varies as a function of plant genotype. To address this hypothesis, we conducted a common garden experiment using vegetatively propagated ramets generated from four Miscanthus genotypes: triploid M. x giganteus ‘Illinois’, the genotype currently used for bioenergy, its parental genotypes M. sinensis, M. sacchariflorus, and a tetraploid M. sacchariflorus. Rhizomes were harvested at planting, and at 20 weeks after cultivation. The diazotroph communities associated with the rhizomes and residing in the rhizosphere were examined using 454 sequencing. 

Results/Conclusions

Although Proteobacteria dominated both rhizomes and rhizosphere, we observed that Miscanthus genotype had a significant effect on recruiting distinct assemblages of diazotrophs for their rhizomes. The effect of plant genotype was less pronounced in the rhizosphere soil, indicating a strong influence of the soil environment on the rhizosphere diazotroph assemblages. Genotypes varied in their ability to enrich specific OTUs. M. sinensis showed the strongest ability to recruit specific OTUs from the rhizosphere soil as well as maintaining the diazotrophs originally living in their rhizomes. Our results suggest that the plant genome structures the plant-associated microbiome, and is particularly influential on the endophytic diazotroph assemblages. Identification of Miscanthus genotypes best able to recruit diazotrophs may enable plant breeding to optimize this trait and improve sustainability of this biofuel feedstock.