Burkholderia phytofirmans strain PsJN advanced development and altered leaf level physiology of switchgrass

Plant growth promoting rhizobacteria (PGPR) were reported to increase the productivity of switchgrass (Panicum virgatum L.), a model biofuel crop selected by the US Department of Energy (DOE). Physiological changes associated with the increased switchgrass productivity upon PGPR inoculation are unknown. Here we measured the photosynthetic rates, stomatal conductance, transpiration rates and water use efficiency weekly on both the upper canopy leaves and lower canopy leaves of switchgrass for 14 weeks and 8 weeks, respectively, on both Burkholderia phytofirmans strain PsJN inoculated switchgrass and control switchgrass. We also tracked changes in growth using a non-destructive photographic method. PsJN inoculation significantly enhanced early total leaf area of switchgrass by 107% (p < 0.0001). However, this beneficial effect linearly decreased with plant age. PsJN inoculation increased photosynthetic rates of upper canopy leaves by 14% (p = 0.0047). Nevertheless photosynthetic rates of lower canopy leaves were decreased by 8% (p = 0.0393). Accelerated leaf senescence and early flowering were also observed in PsJN inoculated switchgrass, which might contribute to slightly lower aboveground biomass at final harvesting as well as increased allocation to reproductive organs. In sum, this study verified advanced development of switchgrass due to PsJN inoculation and suggests that increased photosynthesis of newly developing foliage is related to enhanced productivity.