Switchgrass has been recognized as one of the most promising bioenergy feedstocks for its high biomass yields, stress tolerance, and ability to grow on marginal lands. Switchgrass cropping can increase soil carbon (C) content, facilitating soil C sequestration and mitigating greenhouse gas emissions. Endophytic bacteria may play a significant role in the development of low-input switchgrass biomass production systems by promoting plant growth, increasing nutrient uptake, and/or enhancing its tolerance to stresses. Some endophytic bacteria may indirectly affect host plants via interaction with arbuscular mycorrhizal fungi (AMF), which form a mutualistic relationship with over eighty percent of terrestrial plants. Few experiments have, however, examined how these interactions affect plant growth and the community composition of AMF.
We examined how two plant-growth promoting Pantoea strains (253 and 261c) of endophytic bacteria affect the growth of switchgrass plants, and AMF infection and community composition of AMF in roots. We inoculated individual strains or their combination with germinating seedlings and then transplanted them into soils with different nitrogen availability. Plants were harvested 45 days and 90 days after transplanting into pots, and an array of parameters, including plant height, tiller numbers, shoot and root biomass, and AMF colonization rates of roots, were assessed.
Results/Conclusions
Both Pantoea strains and their combination significantly increased plant root biomass and root AMF colonization rates by 45 days after transplanting. Plants inoculated with strain 253 only significantly increased shoot biomass and tiller numbers. By 90 days after transplanting, only AMF colonization rate was still significantly higher in plants inoculated with endophytic bacteria when no chemical N was added, likely due to depletion of nutrients. When chemical N (60 kg N per hectare) was added, shoot biomass remained significantly higher in plants inoculated with strain 253. Further assessment of their effects on plant nutrient stoichiometry, the community composition of AMF in roots and root-mediation of residue decomposition are underway. Together, our results indicate that endophytic bacterial strains 253 and 261c can significantly promote plant growth and AMF infection in switchgrass, but nutrient limitation may constrain their potential for biomass enhancement. Understanding the interactions among endophytic bacteria, AMF and host plants can help us better deploy beneficial endophytic microbes in the development of low-input production systems.