Plants pull carbon dioxide from the atmosphere and biofuel crops could reduce our demand for fossil fuels. But how much more could these plants do to combat climate change, especially if we used the tools of genetic engineering to tackle the problem?
That's the question posed by Christer Jansson of Lawrence Berkeley National Laboratory and colleagues, who consider all the possible ways that land plants counteract climate change and where genetic modification could play a role in enhancing these processes. They published their work in BioScience.
"The main purpose of this article is to encourage discussion and research into various areas which could help us explore or understand to what extent plants could be altered to enhance carbon sequestration," Jansson said.
Humans emit about nine billion metric tons of carbon a year, about five of which are absorbed by ecosystems on land and water, leaving four to accumulate in the atmosphere and warm the planet.
Plants can sequester carbon temporarily in their leaves, trunks and stems. Once the plants die and other organisms degrade the plant material, the CO2 is released into the atmosphere again.
But plant roots provide longer-term storage, as does burned plant material, which can stay in the soil for hundreds or thousands of years as charcoal.
Genetic modification could potentially improve rates of photosynthesis or the amount of biomass stored in roots, leading to more carbon stored for the long term, the team noted.
"For bioenergy crops, the needs are to grow on marginal land and be tolerant to different kinds of stress, and engineered to grow in saline water or brine rather than fresh water," Jansson said.
"Freshwater is a rare commodity and it will be even more precious in the near future," he added.
"In certain areas, genetic engineering can contribute quite a bit," Jansson said, including improved stress resistance and photosynthesis. "I don't think it's just around the margins. Using proper controls, I think it could be a valid approach."
Bioenergy crops could conceivably offset between five and eight billion metric tons per year by 2050, the team estimated, including improvements using conventional breeding. Genetic engineering to enhance photosynthesis, improve partitioning into root systems and create better stress tolerance, among other things, could increase that by around four billion metric tons, according to the authors.
"We want to emphasize that we do not view plant genetic engineering as a stand-alone procedure but rather as one feature of modern molecular plant breeding," the authors wrote.
In another paper in the same journal, Steven Strauss of Oregon State University in Corvallis argued that the U.S. regulatory system effectively blocks genetic modification from being used to enhance biofuel crops.
"Right now we have a regulatory system that's so strict. We need regulations that address (genetically engineered plants) as a diversity of benefits and a diversity of risk," Strauss said.
Any escape of genetically engineered crops under development into the environment is a regulatory violation, he said, which makes field trials risky to undertake. "You need to get them into the field in early stages. You have to expect some spread into the environment and we have to have some tolerances that allow for that," he said.
"It would be a challenging and sophisticated (regulatory) system, and there would be lots of healthy argument," he said. "But it would be nothing like we have today, where just using a method makes you a criminal."