Plant Feedstock Genomics for Bioenergy
Candidate Bioenergy Feedstocks: An Overview
For biofuels to become mainstream fuels, they must become economically competitive with petroleum. That means farmers have to start with extremely hardy plants that are remarkably resistant to drought, insects, and diseases and can produce high yields on many types of cropland. Since this combination of attributes isn't normally found in nature, researchers must find ways to nurture it in the laboratory.
Which plants are researchers concentrating their efforts on?
To date, the focus has been on perennial, fast-growing herbaceous and woody plants—such as trees, shrubs, and grasses—because they have several general characteristics that make them better suited for biofuel production than annual crops. First, because perennials typically retain significant tissue mass below ground, they rapidly form canopy in the spring, accumulating biomass when many annuals are still seedlings. As a result, their net rates of photosynthetic CO2 fixation into sugars are higher, which increases the total amount of biomass accumulated per acre annually. Second, perennials require little, if any, tillage, saving energy and labor and significantly reducing soil erosion and nutrient loss. Third, perennials typically withdraw mineral nutrients into their roots at the end of the growing season, thereby reducing fertilizer costs. Because they have few natural pests, they also can be produced with little to no pesticide use. Finally, developing perennials for energy crops could facilitate the use of genetically diverse, mixed stands rather than monocultures of single cultivars.
Which plant feedstocks show the greatest potential for bioenergy production?
No single plant species will be optimal for all agroecoregions. Consequently, DOE's Office of Science and other federal agencies are developing a suite of new crops and new varieties of existing crops for a range of different soil types and climatic conditions.
Specific feedstocks under consideration include:
- Trees—poplar, hybrid poplar, willow, silver maple, black locust, sycamore, sweetgum, and eucalyptus
- Perennial grasses—switchgrass, reed canary grass, prairie cordgrass, Brachypodium distachyon, Miscanthus, and tropical grasses
- Food and forage crops—wheat and alfalfa
- Sugar crops—sorghum
- Agricultural wastes—corn stover and rice stover
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| Click image to see a chart showing the attributes of an ideal biomass crop. Source: U.S. DOE. 2006. Breaking the Biological Barriers to Cellulosic Ethanol: A Joint Research Agenda, DOE/SC/EE-0095. |
These plant species were selected as crop development models based on their performance in screening trials, potential for broad distribution, ease of propagation, environmental benefits, and status of genetic information. Such crop models can be used to rapidly test strategies that might improve their usefulness in bioenergy production.
What can dedicated perennial biofuel feedstocks offer?
Advantages
- environmental sustainability
- predictable supply
- uniform quality
- high yield per unit of area
- high energy output/input ratios
- vast potential supply
Benefits
- soil and water conservation
- wildlife habitat
- CO2 sequestration
- domestic energy supply
- rural agricultural development
- possible co-products, such as pulp and paper, chemicals, forage
Management
- single establishment period
- relatively low agro-chemical inputs (fertilizers, herbicides, pesticides)
- minimal cultivation
- multiple crops and harvesting options
- switchgrass harvested annually or twice annually
- trees harvest on 3-8 year cycles, minimizing storage requirements
[Text largely adapted from Breaking the Biological Barriers to Cellulosic Ethanol: A Joint Research Agenda, U.S. Department of Energy Office of Science and Office of Energy Efficiency and Renewable Energy, June 2006, DOE/SC-0095, and the ORNL Bioenergy Feedstock Information Network.]
