Carbon fiber is one of the strongest and most resilient materials on the market, used in everything from car frames to body armor. It's also incredibly expensive to make. But one plant biologist says that in fifty years, we'll be growing it on trees.
This may sound like a weird assertion, but consider that trees are already the source of two materials that have pretty much built human civilization: wood and paper. Humans have been processing trees into other materials for thousands of years. Now these extraordinary plants are about to transform our civilizations again, thanks to twenty-first biorefineries and genetics. The best part? The whole operation will be carbon neutral.
The first time I met Gerald Tuskan, he was addressing a packed audience at the Joint Genome Institute user group meeting in California earlier this year. After presenting his work on plant genetics, he said something that I couldn't quite believe: "One day, we'll make and fuel our cars with trees." I had to find out more.
I caught up with Tuskan by phone in his office in Oak Ridge National Laboratory, a massive facility funded by the U.S. Department of Energy, about 150 miles east of Nashville. Situated next to a long, winding river in thickly-forested hills, it's the perfect place for a tree scientist to imagine the future. Tuskan has devoted his life to studying the development of trees, especially the common poplar (pictured above). He pauses thoughtfully between sentences, reminding me a bit of a small, clean-shaven version of the tree Ents from Lord of the Rings.
Right now, Tuskan is fascinated by a substance called lignin. Trees are mostly made up of substances called cellulose and hemicellulose, which contain sugars that can be fermented into ethanol fuel. But one third of the tree's weight comes from lignin, a fibrous polymer that helps strengthen plant cell walls. Historically, lignin has been a waste product in ethanol production. Not anymore. "We can melt it and spin it into carbon fibers," Tuskan says. Or we could use it to make plastic. "For a car, the tree could be deconstructed then reconstructed into the body, frame, interior, and things like that."
With a tensile strength greater than steel, carbon fiber made from lignin has countless uses that go beyond making a car. Already, the petroleum-derived version of the material is used in everything from airplane propellers to retrofitted bridges. The realquestion is whether we can grow trees that yield lignin in the right amounts, with the right properties for various industrial applications. That's where tree genetics come in.
Poplars by Claude Monet
The poplar tree's genome has been sequenced and it has 42 thousand genes — roughly twice the number as a human. It turns out that this is typical for a perennial plant like the poplar. Though we animals think of ourselves as far more sophisticated than plants, Tuskan explained that trees have to be a lot tougher and more resilient than the typical animal. He explained:
Humans or mice or elephants can move. If it's cold they can go underground or build shelter. Perennial plants have to stand there and take it for thousands of years in some cases — they have to be equipped biochemically for a drought, ready for heat or cold, ready for an insect attack. I think that's part of why plants have larger arrays of genes — that's their way of surviving.
Out of all these genes, only a handful may turn out to be useful for industry. "Half of the genes have no known function," Tuskan said, "and with lignin it's probably somewhere between a dozen and three or four dozen genes that will turn out to be important."
A lot of what Tuskan's lab does with poplars is an effort to link the behavior of specific genes to physical traits in the tree. This kind of analysis is called a genome-wide association study or GWAS, which everybody in the field pronounces "gee wass," like J-Lo for genome geeks. "Basically it's figuring out the genome's relationship to the phenotype," said Tuskan.
He and his colleagues have already had some success isolating genes that control various aspects of the tree's metabolism. In one case, they were able to start and stop the growth of a symbiotic fungus in poplar tree roots. Ultimately, Tuskan would like to have genetic switches that control many aspects of the poplar's development. Farmers could do things like grow a tree that's designed to have more lignin or less, depending on what the market demands.
To understand the full impact of Tuskan's vision, you have to imagine a future where poplars have become a cash crop like corn. Today, we grow corn for everything from popcorn to fuel, and there are many strains of corn that have been genetically optimized for use in these areas. If GWAS analysis of the poplar is successful, soon we might be growing many strains of poplars, some of them designed to produce lignin that can be used in jet aircraft and some to produce lignin for the plastic bodies of laptops.
"Depending on what your customer wants, you might vary or modify the molecular weight of the lignin," Tuskan mused. "Chemical engineers and polymer scientists would work with geneticists and plant breeders to target the right combination of genes."
Poplar farms would be unlike any other farms we have today, however. Unlike most crops, which are annuals, poplars grow year-round. Plus, the poplars create their own ecosystem, which has to be nurtured as much as the trees themselves do. Tuskan explains that farmers would harvest in winter, which is when the leaves have fallen. But this isn't to make things easier when it comes to extracting lignin. Instead, it's because the leaves are crucial for the wildlife habitat and for preventing soil erosion.
"80 percent of the land would still have trees at any given time," Tuskan explained. Farmers would cull only about one fifth of the crop each year. And they wouldn't harvest in patches — there would be none of the clearcutting patterns we know so well from the logging industry. Tuskan imagines a forest that is thinned equally, everywhere, with trees being culled only after five to eight years of maturation. As a result, the habitat would have a chance to remain robust and diverse.
Photo of a bald eagle in a poplar by Paul Cyr
Tuskan describes poplar agriculture using terms like "habitat," and calls tree branches "crown architecture." He wonders about how to make his future poplar farm more attractive to birds. Will they like steep or horizontal angles in the branches? If it turns out they like horizontal branches, "that's all under genetic control," he said. I'm left with a picture of a farm that's built for mice, squirrels, birds and bugs — as well as crops for humans.
Tuskan is imagining a farm that's treated like an ecosystem rather than a monoculture. And that may be even more revolutionary than the notion of using genetic switches to produce carbon-fiber-ready poplars and bird-optimized tree branches.
The perennial poplar farm also changes the economic game of agriculture. "You have to have a stable demand and product market to do this," Tuskan explained. "It will take years to produce the right plant material, and then several years before harvest." So farmers have to predict market demand as many as eight years in advance. "That's the downside of perennial systems, though upside is positive impact on soil and wildlife," Tuskan said.
Of course the upside isn't just saving the ecosystem. Farmers who invest in perennial farms have a lot more options than ones who grow crops like corn or fruit. They can wait out a tough season, and their crops won't spoil. The trees will keep growing, and may wind up being more valuable the following year. And industries that use trees instead of petroleum for their products are capturing carbon rather than pumping it into the atmosphere. "There's no way to attach a dollar value to that," Tuskan said. But in many parts of the world, where carbon tax systems and their ilk are becoming a reality, that could soon change.
Given the demand for the products that poplars make — from fuel to plastic — Tuskan believes that a perennial tree farm industry could exist in fifty years. That's roughly the same amount of time it took the corn industry to move from strictly food crops to the diverse array of industrial uses corn has today.
Experimental poplar farm photo via Energy Digital
Fifty years ago, this kind of farm would have been inconceivable. That was before we understood carbon cycles and the damage caused by burning fossil fuels. It was also before we had genome sequencing. Today, however, it's impossible to think about the future of energy from a scientific perspective without also thinking about ecosystems. That's why a scientist funded by the U.S. Department of Energy can say that his inspiration comes from the forest.
"When I was in the 8th grade I wanted to be a forest ranger," Tuskan said with a laugh. "I thought it would be great to sit in a tower and watch for fires. That seemed romantic." But then he got interested in how trees grow, and his youthful enthusiasm became an adult fascination with how genetics and chemistry control trees' form and function. Still, his first love remains the forest. Tuskan believes that tree farms won't just save us by weaning humanity off petroleum products. It will save forests as well. He told me:
I don't envision cutting down forests for these plantations. To get high yield, these plantations have to go into agricultural settings, on agricultural quality land. You can't cut down redwoods and put them there. So I think it's a way of preserving natural forests. If we can get more fiber per unit area per unit time, that's less trees we have to cut down in the forest. By intensively managing these byproduct plantations, we can preserve the native forest.
You can read more about Tuskan's work on his website.
Annalee Newitz is the editor-in-chief of io9. She's also the author of a book called Scatter, Adapt and Remember: How Humans Will Survive a Mass Extinction.