Trees: A Poplar Source for Biofuels
Jennifer Martin, CSREES Staff (202) 720-8188
October 15, 2007
By Stacy Kish, CSREES Staff
There is no simple solution to the energy problem. Crops, such as corn, compete with the food supply. Poplars and other trees could provide a sustainable alternative for ethanol production; however, they require costly pretreatment before processing into ethanol. Researchers at North Carolina State University (NCSU) have identified a potential solution to the problem.
Currently, the ethanol industry provides about four billion gallons of ethanol to the fuel market, which is expected to grow. Developing a process that effectively makes ethanol from cellulose derived from different types of plant biomass, particularly wood, remains difficult due to one significant barrier. The barrier is known as lignin.
Lignin is a glue-like polymer in the cell wall of plants that surrounds cellulose to provide strength to fibers and to resist microbial decay. The strength allows trees to stand tall so they can utilize the sun's energy for photosynthesis. Lignin is also second only to cellulose as the largest pool of non-fossil organic carbon, constituting up to a quarter of the dry mass of wood. Unfortunately, lignin is difficult to breakdown for cellulose extraction and requires chemical pretreatment. Chemical pretreatment raises the cost for using plants as the source of cellulose.
Vincent Chiang, co-director of the Forest Biotechnology Group at NCSU, and his colleagues, Ron Sederoff and Hou-min Chang, have identified lignin production genes in fast-growing poplar trees. They have modified the genes to reduce the lignin content of trees by as much as 50 percent. This finding will greatly reduce the expensive pretreatment currently used to extract cellulose.
'We really don't need to create a strong tree for fuel as long as the tree can grow rapidly for a short time,' Chiang said. A reduction in lignin content of 10 to 20 percent would allow much more efficient production of biofuel without impeding the tree's growth.
The scientists are also tackling this problem from another perspective. They are looking at the big picture of how wood is formed during plant growth. By examining how genes, proteins and metabolic pathways work together, the scientists hope to gain a better understanding of how lignin is formed. Understanding the broader context of lignin production may allow the scientists to engineer poplar trees with an altered lignin chemical composition that could more easily decompose during biofuel production.
The scientists believe both processes could significantly improve poplar tree biomass availability for ethanol production in the next five to 10 years. For a large-scale production of fuel from wood, similar work is needed on other tree species, such as pines to provide for the long-term energy needs.
The USDA's Cooperative State Research, Education, and Extension Service (CSREES) funded this research project through the National Research Initiative (NRI) Biobased Products and Bioenergy Production research program. CSREES advances knowledge for agriculture, the environment, human health and well-being, and communities by supporting research, education and extension programs in the Land-Grant University System and other partner organizations. For more information, visit www.csrees.usda.gov.