Poplar trees genetically engineered to fight climate change start their lives in a San Francisco lab. LIVING CARBON

A California biotech company seeking to create fast-growing trees that can rapidly soak up atmospheric carbon dioxide has announced its first experimental results: the firm’s genetically enhanced poplars grew more than 1.5 times faster than unmodified ones in lab trials. Plant scientists applaud the news, but caution that much more work is needed before engineered trees can start to help curb climate change.

“It’s a great first step,” says Sophie Young, a plant biologist at Lancaster University who is not involved in the work. But, she adds, there’s “a big caveat”: The trees grew in a carefully controlled greenhouse as opposed to the outdoors.

Scientists and environmentalists have promoted tree planting as a promising and easily expandable way to draw down atmospheric levels of carbon dioxide, the primary cause of global warming. Trees, which are roughly half carbon by dry weight, absorb the gas from the air and turn it into stable forms of carbon such as wood and roots.

But how fast trees soak up carbon is limited by numerous factors. One key constraint is the rate of photosynthesis, the biochemical process trees use to convert carbon dioxide into sugars and ultimately wood. Nearly all trees use a relatively inefficient form of photosynthesis that produces a toxic byproduct called phosphoglycolate, which the plants must then remove through a process called photorespiration. That uses energy that could otherwise go toward growth.

To sidestep the problem, researchers with a company called Living Carbon used a bacterium to insert genes from pumpkin and green algae into poplar trees. The foreign genes enabled the trees to have lower photorespiration rates and to recycle carbon from phosphoglycolate into sugars essential to growth.

Other researchers previously engineered a similar trait into tobacco plants. But, “To my knowledge [the approach] has never been tested in a tree before,” says Steve Strauss, a forest geneticist at Oregon State University, Corvallis, who serves on Living Carbon’s scientific advisory board and is collaborating with the company on research.

Living Carbon, founded in 2019, is growing the engineered poplars inside a converted music recording studio in San Francisco. Some of the trees have grown so tall they bumped into the ceiling. “As someone who spends my time on Zoom, it’s very nice” to be in the greenhouse, quips CEO Maddie Hall.

In trials lasting about 4 months, the engineered poplars put on 53% more weight than control trees without the added trait, the company reports in a study posted today on the preprint server bioRxiv, which does not require formal peer review.

Those numbers are “encouraging, but they’re not overwhelming,” says plant biologist Donald Ort of the University of Illinois, Urbana-Champaign, who led the tobacco enhancement project. And he cautions that even promising lab results often falter in more realistic tests. Coddled trees that grow fast indoors may wilt in tougher outdoor conditions or need lots of water and fertilizer to sustain high growth rates. And once nearby trees begin to block sunlight, growth often slows. To test the endurance of Living Carbon’s poplars, Strauss has begun to grow some in a field in Oregon; he hopes to report results next summer.

Even if field trials pan out, Living Carbon could face a lengthy regulatory process in order to sell the trees. In the United States, federal regulators have never approved the release of a tree engineered for fast growth. Their review of a chestnut tree engineered to resist a devastating imported blight has been underway for more than 2 years, with no timetable for completion. (Company leaders say a poplar they engineered using a different method does not need federal regulatory approval, and they plan to plant that tree on private land as soon as late this year.)

Some advocacy groups, meanwhile, oppose the release of any transgenic trees, fearing unintended ecological impacts. And most programs that certify forest products as sustainable currently forbid the use of engineered species. That creates “an almost de facto market ban” on using them for consumer products, Strauss says. Given all the issues, Ort says commercial deployment of Living Carbon’s trees may be 10 to 15 years away.

Living Carbon may have the resources to weather such a wait. Company leaders say they are backed by nearly $15 million in venture capital funding. And fast-growing trees aren’t the company’s only interest: It is also trying to engineer trees to take up heavy metals from degraded soils. Company leaders hope those metals could give the wood antifungal properties that will reduce its decomposition rate, enabling it to store carbon longer.

Strauss, for one, believes the urgency of addressing the climate crisis outweighs potential risks associated with transgenic trees. “We don’t have the luxury,” he says, “to wait for 30 years and make sure nothing can possibly go wrong.”

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By: Gabriel Popkin || Science