Now a Californian startup has taken the same approach, but this time with poplar trees. In a non-peer-reviewed preprint first posted on February 19, scientists at Living Carbon claimed that by inserting new genes into poplar trees, they can make the plants grow 53 percent more quickly than their non-edited equivalents. Both sets of trees were grown under controlled conditions that differ significantly from the ones the plants would face in the wild, but Hall hopes that the edited trees will supercharge tree-planting plans by drawing down atmospheric carbon more quickly.
“Our belief is that climate change is a problem of relative rates. And also it’s one that we can’t just solve with man-made, intensely managed human processes like direct air capture,” she says. (Direct air capture means building devices that could scrub atmospheric carbon dioxide—or others that might trap methane—but by one recent estimate it could take 10,000 such machines to make a difference in CO2 levels.) Living Carbon’s eventual business model will be to plant its genetically engineered trees on land leased from private landowners, then give those landowners a share of the money earned by selling carbon credits earned against the growth of the trees.
When most plants photosynthesize, they produce a toxic byproduct called phosphoglycolate, which they then have to use energy to break down—a process called photorespiration. Living Carbon’s edited trees have extra genes from algae and pumpkin that help the plant use less energy to break it down, as well as recycling some of the sugars created by this process. This pathway was an obvious target for making plants more efficient, says Yumin Tao, Living Carbon’s VP of biotechnology. “You channel that byproduct into energy and nutrients for plant growth,” says Tao. And more plant growth means more carbon captured.
Tao and his colleagues grew the genetically engineered poplars for 21 weeks in a lab before harvesting and weighing them to see how much biomass they’d accumulated. The best-performing seedling had 53 percent more above-ground biomass than non-edited plants. Tests also showed that the edited plants took up more carbon than their non-edited cousins, an indication that these plants had a higher rate of photosynthesis.
“It’s a really exciting first step,” says Cavanagh, who was not involved in Living Carbon’s research. But she cautions that we don’t know whether these trees will be better at storing carbon in the long run. Living Carbon’s poplars were harvested after only five months, but in the wild the trees can live for more than 50 years. Only further studies will reveal whether the edited trees will continue to grow quickly as they mature. Their growth rate might slow, or they might become so unhealthy that they fall over and release all that carbon back into the atmosphere when they rot. “Is the effect you see at the seedling phase the same at different stages of maturity, or does the plant fight back?” asks Cavanagh.
Soon this will be put to the test. Living Carbon has already planted 468 of its photosynthesis-enhanced trees in central Oregon, part of a field trial it’s running with Oregon State University. The company will analyze how quickly the trees grow over longer periods of time and also how they perform in different environments. It has also secured agreements to plant poplars created using a slightly different technique on around 3,500 acres of private land in the US, with the first plantings scheduled to start in late 2022, according to Hall.