PsJN advanced the development and improved drought tolerance of Switchgrass

Background/Question/Methods

Burkholderia phytofirmansstrain PsJN is a well-studied endophyte, which was reported to increase the biomass production of switchgrass cv. Alamo seedlings. However the physiological processes which result in higher yield in PsJN inoculated switchgrass is unknown. Furthermore, the effect of PsJN on drought tolerance of switchgrass is unclear. Since PsJN has been found to improve tolerance of grapevine to low temperature stress, it may also improve switchgrass drought tolerance through similar mechanisms because many stress responses share the similar mechanisms. In one experiment growth of PsJN seedlings were monitored using a non-destructive photographic technique accompanied with leaf gas exchange measurements. A second experimentt consisted of two successive drought-rehydration cycles to examine drought tolerance of PsJN inoculated swtichgrass.  In the first drought-rehydration cycle, the control group received 1300 ml water/week/pot, the stressed group received only 1/3 that amount for 40 days.  Then all treatments were rehydrated to field capacity for 10 days. After full hydration, all treatments received no further water until photosynthesis rates reached zero. Immediately, the pots were rehydrated to field capacity to monitor recovery.

Results/Conclusions

Both development and senescence of switchgrass were accelerated by PsJN inoculation. The results were consistent among different growth parameters (leaf area, height and tiller number) in both experiments. Leaf area, height and tiller number in PsJN inoculated plants were significantly higher than those of control plants when the seedlings were younger than 10 weeks. After 10 weeks, the growth differences between PsJN inoculated group and non-inoculated group gradually diminished. Accompanied with faster development of PsJN inoculated switchgrass was early senescence, which was indicated by earlier drop in photosynthesis rate of the same leaf and larger number of the dead leaves. Mild drought stress stimulated the growth of PsJN inoculated switchgrass seedlings but not the control group. In the subsequent severe drought stress, pre-drought stressed switchgrass had higher photosynthesis rate than watered switchgrass through the second drought cycle. This pre-hardening effect was more pronounced in PsJN inoculated plants.  The data also showed that PsJN inoculated swtichgrass developed faster and showed better acclimation to mild drought stress.