Effects of endophytic bacteria on plant growth and arbuscular mycorrhizal fungi in switchgrass

Background/Question/Methods

Switchgrass is considered a leading bioenergy crop because of its ability to grow in marginal lands. One major reason for high switchgrass adaptability to infertile soils is its extensive symbiotic associations with mycorrhizal fungi. Recently, some endophytic bacteria have been shown to enhance plant growth in artificial growth media and there is a concern that these bacteria and arbuscular mycorrhizal fungi(AMF) may compete for carbohydrates in roots. To our knowledge, however, no experimental evidence has been reported. We examined the impact of one endophytic bacterium, Burkholderia phytofirmans strain PsJN, on mycorrhizal status of switchgrass cv. Alamo under both greenhouse and field conditions. We chose two sites with distinct soil fertility (i.e., a infertile soil with low organic N vs. a fertile soil with high organic N) for the field trial and one moderately fertile soil for a greenhouse test to assess the bacterial effect on plants and AMF in roots.

Results/Conclusions

The bacterial endophyte significantly increased switchgrass growth at both sites but showed different effects on AMF. AMF colonization of roots was 60% higher in the PsJN-inoculated than non-inoculated plants in the low fertility soil. In contrast, endophytic bacterial inoculation did not have significant effects on AMF infection in the high fertility soil. In addition, PsJN bacteria led a small but significant increase in AMF colonization of roots in a moderately fertile soil in the greenhouse experiment. Together, these results suggest that the soil fertility status may affect endophytic bacterial effects on AMF, illustrating the potential for utilization of beneficial bacterial endophyte in switchgrass establishment in low fertility soils.