Low-Input Production of Switchgrass Using Plant Growth Promoting Rhizobacteria.

Switchgrass (Panicum virgatum) is being examined as the prime candidate for biofuel feedstock production in North America because it can be grown on marginal lands with minimal agricultural inputs and thus does not displace food production. Variety trials were conducted in Ste-Anne-de-Bellevue, Quebec, Canada (45°28’N 73°45’W) on 11 different upland switchgrass varieties including Cave-In-Rock, Carthage, and several cultivars from the U. of Nebraska and Oklahoma. The trial was initiated in 1996, and managed until 2000 after which no fertilizer was applied. The switchgrass has continued to produce high biomass yields without N fertilization, which suggests an alternative N source perhaps through biological nitrogen fixation. We hypothesized that a) indigenous populations of rhizosphere N₂-fixing bacteria have provided switchgrass with the N necessary for substantial biomass growth, and b) productivity differences amongst varieties are due to variation and abundance of N₂-fixing bacterial populations.

In 2008, rhizosphere soil, root and rhizome samples were collected from this field site. Endophytic (> 300) and epiphytic (> 500) putative N₂-fixing bacteria were isolated on N-free solid media. Bacterial screening bioassays were performed in a growth chamber on inoculated and uninoculated (control) switchgrass plants (P.virgatum cv. Cave-In-Rock) fertilized with N-free Hoagland’s solution. Isolates that show plant growth promotion will be selected for identification using phylogenetic anaylsis of the 16S rRNA. Amplification of nifH gene will be used as a marker for N₂-fixation capability. Those isolates that show production of the greatest amount of plant biomass will be chosen for further field experimentation. The results of this project will advance our management of purpose grown grasses and existing grasslands. The development of biofuel crop systems that require low N input will improve both the economics and energetics of biofuel production, enhancing the use of biofuels as a sustainable energy source and support rural renewal.