Argonne, University of Chicago researchers pursue grasses as Earth-friendly
biofuel
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ARGONNE, Ill. (July 18, 2008)—At a small site on the Batavia campus
of Fermilab, ecologist Julie Jastrow of Argonne National Laboratory pushes
the scientific frontier in a new and exciting way: She watches the grass
grow.
As part of an effort to develop a new collection of alternative fuels, Jastrow
and her colleagues from the U.S. Department of Energy's (DOE) Argonne National
Laboratory and the University of Chicago have planted seven different combinations
of native Midwestern prairie grasses on the 13-acre site at Fermilab's campus.
The experimental facility that Jastrow planted in June will examine the sustainability
of different perennial bioenergy crops – plants that could be turned into energy
either by being burned directly or by being converted into cellulosic ethanol.
While crops with high starch or sugar contents -- most notably corn grain
and sugarcane -- are the focus of current bioenergy applications, botanists
have also seen potential in perennial grasses. "Right now, if you looked
at the list of perennial bioenergy crops being studied, switchgrass will be
at the top of the list," Jastrow said.
According to Jastrow, DOE began to consider
perennial forage crops
as possible sources of alternative fuels during the oil crisis of the late
1970s and early 1980s. As Americans lost access to imported oil due to political
instability in the Persian Gulf states, scientists saw an opportunity in the
open grazing land of the Great Plains and the prairie remnants of the Midwest,
where switchgrass and other native perennial grasses grow in dense stands from
four to eight feet high.
The Argonne ecologists are working with several varieties, or cultivars, of
switchgrass that differ in geographic origin and genetic attributes. In addition
to switchgrass, they planted a number of other species, including big bluestem,
Indiangrass and Canadian wild rye.
Jastrow and her colleagues are seeking to determine which grasses produce
high yields of harvestable biomass while also pumping the most carbon underground
through root growth. When roots die and decompose, some carbon is sequestered
in soil organic matter, and nutrients such as nitrogen are recycled to sustain
future plant growth.
“We expect to use some of the new genetic, bioinformatics, and molecular tools
available through Argonne's Biosciences and
Mathematics and Computer Science divisions, the joint Argonne-University of
Chicago Institute for Genomics
and Systems Biology, and Argonne's Advanced
Photon Source to help tease out how differing plant traits and microbial communities
interact in the soil environment to control these processes,” Jastrow explained.
In general, researchers interested in perennial grasses as bioenergy crops
typically compare species or cultivars one at a time in “monocultures.” But
recent studies suggest that planting a diverse mixture of grass species might
lead to greater sustained yields over time.
"Diverse plantings are better equipped to deal with annual variations
in climate and probably have fewer problems with pathogen buildup than monocultures," Jastrow
said.
But growing a feedstock consisting of several different grass species would
complicate up-and-coming efforts to convert the cellulose in plant matter into
ethanol, a process that might require the use of a separate set of microbes
for each grass species. Jastrow and her colleagues believe they can avoid this
problem while reaping the benefits of diverse plantings by using a mixture
of switchgrass cultivars to increase genetic diversity.
Although a number of other grass species grew abundantly in the prairies of
the Midwest and Great Plains, switchgrass soon found favor among botanists
selecting grasses for grazing and biomass production because of its unusually
high response to fertilization.
"Most of the other prairie grasses," she said, "are more nutrient-use
efficient. If you fertilize them, it's all excess, and they don't grow much
larger. Switchgrass, however, can really take off when it's fertilized."
Next year, after the grasses are established, half of the area planted with
each of the seven cultivar/species combinations will be fertilized annually
while the other half will remain unfertilized.
The addition of fertilizer, however, represents a "carbon cost" to
the environment that derives from the process of making the fertilizer as well
as the fuel for the vehicles required to ship and spread it; the planting,
harvesting, transporting and processing of feedstocks creates other carbon
costs as well. In Jastrow's view, the "carbon balance" of a particular
type of grass – the difference between its "carbon cost" and the
amount of carbon it offsets or sequesters – has to be considered when evaluating
its potential effectiveness as a bioenergy crop.
"One of our ideas," she said, "is that maybe you won't get
as much production with some of the other grasses; but if you don't have to
fertilize or if these grasses are better at sequestering carbon in the soil,
then the overall carbon balance might be about the same or even better."
Jastrow's collaborators on this project include Mike Miller and Roser Matamala
from Argonne and Geoff Morris and Justin Borevitz from the University of Chicago. Jastrow coordinates Argonne's contributions to the DOE Consortium
for Research on Enhancing Carbon Sequestration in Terrestrial Ecosystems (CSiTE), which
also includes scientists from Oak
Ridge and Pacific Northwest national laboratories.
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Department of Energy's Office
of Science.
By Jared Sagoff.
For more information, please contact Angela Hardin (630/252-5501
or ahardin@anl.gov) at Argonne.
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