High pump prices fuel interest in renewable altenatives

As gasoline and diesel prices continue to hover at near-record levels, and the United States’ dependence on petroleum imports increases, the public is renewing interest in fossil fuel alternatives.

The country’s agriculture industry is one source of domestically produced options to conventional energy. In fact, biomass — plants and plant-derived material — provides the only renewable alternative for liquid transportation fuel.

Ethanol, traditionally made from corn, is familiar as an alternative fuel and a pollution-reducing gas additive.

“One of the problems with ethanol from corn is that it takes a lot of energy to produce,” says Dr. Zeng-yu Wang of the Noble Foundation in Ardmore, Oklahoma.

It is possible, however, for fuel ethanol to be made from plant fiber (cellulose and hemicellulose) biomass. Switchgrass, a fast-growing perennial warm-season native grass with a wide geographic distribution, is one of the most promising energy biomass sources because of its adaptability, hardiness, longevity and high biomass production.

Wang, an associate scientist in Noble’s Forage Improvement Division, recently received funds to investigate improving ethanol production from switchgrass. Wang’s $670,000 grant was one of 11 awarded as part of the United States Department of Agriculture and Department of Energy’s joint 2005 Biomass Research and Development Initiative.

Wang says the process for making ethanol from switchgrass is essentially the same as the one used with corn — the plant material is broken down into its component sugars, and then those sugars are fermented to produce ethanol.

“The energy required to make corn ethanol is positive at about 1.34, but that is dwarfed by the possible five-fold energy balance — the amount of energy put into a process compared to how much energy is produced — for ethanol production from cellulose and hemicellulose.”

While switchgrass has abundant sugars in the form of cellulose and hemicellulose, extracting them is difficult because of a third plant fiber component, lignin.

“Lignin is like the cement between bricks in a wall,” Wang says. Lignin holds the cellulose and hemicellulose together and inhibits breakdown into the sugars needed for ethanol production.

Wang’s proposed method for improving switchgrass for ethanol production involves using genetic engineering to reduce lignin in the plants.

“We are going to down-regulate, or ‘knock out,’ genes responsible for making the enzymes that lead to lignin production,” Wang says. “We can’t completely knock them out, though, because plants couldn’t grow without some lignin. We want to reduce it to the point where it improves ethanol production potential without negatively affecting plant growth.” One of the down-regulation methods Wang plans to use has been shown to reduce lignin content significantly in another grass species, tall fescue. The second method he plans to try has been effective in alfalfa.

Construction and screening of a switchgrass cDNA library — a large pool of genes from the species — is currently underway, and Wang anticipates initial genetic transformations of plants will be completed in December 2006. He says the transgenic switchgrass plants will be incorporated into Noble’s breeding program by 2008.

“Fossil fuels sooner or later will deplete,” Wang says. “Therefore, renewable energy from plants will be necessary.”

A potential side benefit of Wang’s lignin reduction work in switchgrass is that the same strategy can be applied to other species, particularly forage crops.

“Reduced lignin leads to improved digestibility of plants when they’re being grazed by ruminant animals,” he adds.

In announcing the Biomass Research and Development Initiative grant recipients, Agriculture Secretary Mike Johanns says USDA and DOE’s cooperative conservation partnership benefits the United States with enhanced energy security, a cleaner environment and revitalized rural economies.