John Carlson also is studying the use of trees for biomass. The molecular biologist served on a steering committee for the International Poplar Genome Consortium, which helped the U.S. Department of Energy chart a path for the ground-breaking genome sequencing of the poplar tree.

Cottonwoods, hybrid poplars, and aspens are being used in a variety of ways, ranging from paper production to carbon sequestration. Penn State biomass scientists are interested in developing fast-growing trees as a source for renewable, biobased products.

Biological engineer Jeff Catchmark is studying the construction of plant cell walls in an effort to unlock the biofuels potential they protect.

“The sequencing of the poplar genome (the genetic material of an organism) is a bonanza for researchers seeking to understand how individual genes influence the growth of trees and their adaptation to the natural environment,” Carlson explains. “We are trying to apply this knowledge to the breeding of fast-growing trees capable of producing wood, fiber, and energy on a smaller amount of land.”

Trees in the Populus genus, such as cottonwood, hybrid poplar, and aspen, have emerged as model organisms in forestry for the same reasons that Populus was chosen as the first tree genome to sequence—rapid growth rate, small genome size, and widespread use in plantation forests, Carlson explains. “Cottonwoods, hybrid poplars, and aspens could play a role in improving the environment, displacing imported oil, and creating domestic jobs,” he says. “But first, scientists need to better understand the biology of Populus, for which the genome sequence provides the blueprint.”

But before biofuels can be made in any quantity from woody plants such as trees, scientists must learn how the cell walls can be broken down so that the plant’s constituent sugars can be converted to an alcohol such as ethanol. “We just started a new project in which we are trying to better understand disassembly of the cell walls,” says biological engineer Jeff Catchmark. “As we are trying to develop methodology to disassemble plant materials, it would be helpful to know how the cell wall is put together. We need to identify the components and understand how all these fibers are connected and how cellulose is formed. If we knew exactly how the cell wall is put together, we might be able to find out how to take it apart.”

Catchmark and colleagues are using novel atomic force microscopy techniques to study the role that substances called “expansins” play in cell walls. “We are placing the plant cell wall under tension in solution and measuring the change in its morphology when exposed to expansins and other enzymes,” he explains. “It’s a promising line of inquiry that might yield new insights into the structure of the plant cell wall, which would be useful in the design of new cellulosic materials. The idea is that someday we might genetically modify plants for ethanol production.”

Wood chemist Nicole Brown also is wrestling with the question of how to break down the cell walls of woody plants. Collaborating with other researchers around the university, she has been pulled into biomass research because of her expertise on how wood polymers behave. Polymers are long strings of molecules that determine the structure of materials such as trees.

“After plants are genetically manipulated to produce different kinds of enzymes and proteins, we study how those compounds affect the properties of plant polymers,” she says. “The thought is that these protein and enzyme-based modifications will make the woody tissue easier to disassemble. That will make it easier to access the sugars that will make ethanol.”

Plant molecular biologist Mark Guiltinan also studies the effect of enzymes in the breakdown of another important source of energy from plants: starch. He and food scientist Donald Thompson have been working with corn, evaluating the way starch structure can affect the breakdown of starch to sugars. “When we are scaling up a huge industrial biofuels process, if we can increase the digestibility of starch we can make the process more affordable,” he says. “Even if we can increase the digestibility only a little bit, it will have a huge impact on the economics of a project.”

Although Guiltinan’s work wasn’t initially aimed at biofuels, it was funded by the U.S. Department of Energy. “Yeast has been turning sugars into alcohol for centuries,” he says. “Starch is like the battery of a plant where sugars are stored as energy for later. We’re studying corn starch biosynthesis to acquire knowledge about the basic process.

“Starch is synthesized by enzymes. It is amazing how little we know about this subject. Starch is being used from many sources around the world—from corn kernels, sweet potatoes, potatoes, and the roots of cassava—for foods. In the future, it may provide material for biofuels production.”

Penn State researchers are focusing not only on crops and plants to create biofuels. They also are exploring the use of agricultural byproducts for generating energy. One of the most promising is manure, which through a process called anaerobic digestion can produce a lowgrade natural gas.

An anaerobic digester system is an enclosed tank that excludes oxygen and through which manure is passed and broken down by naturally occurring bacteria, producing biogas. The biogas is 55 to 70 percent methane, which can be used to generate electricity or replace other stationary energy needs, such as heating water or buildings or powering equipment.

Manure digestion is not new, but it has never produced the amount of energy that scientists had hoped for. Thirty years ago an experimental manure digester was located on Penn State’s campus in Centre County. In the midst of an energy crisis brought on by uncertainty about the flow of Middle-Eastern oil, the pilot project was thought to have considerable promise for demonstrating how biogas could be produced from animal manures or other organic wastes on Pennsylvania farms. Now, if you know where to look, you can find the remains of the digester’s foundation, crumbling and forgotten behind the university’s dairy barns, across the road from Beaver Stadium.

The project made its mark—by the end of the 1970s, four manure digesters were up and running in Pennsylvania, using technology proven by the Penn State digester. They remain today among the longest continuously operating onfarm digesters in the country.

“But interest in anaerobic digesters producing methane and generating electricity on farms never really caught on, even though it was feasible,” says agricultural engineer Bob Graves. “It never made economic sense for most farms because once energy supplies stabilized, oil prices were still relatively low. Also, there were many competing uses for a farmer’s capital and management time that provided quicker paybacks.