Plants speed up their respiratory metabolism as temperatures rise, leading to a long-held concern that as the climate warms, the elevated levels of carbon released from plants' ramped-up metabolism could flip global forests from a long-term carbon sink to a carbon source, further accelerating climate change.
However, a new University of Minnesota study of more than 1,000 young trees has found that plants also adjust — or acclimate — to a warmer climate and may release only one-fifth as much additional carbon dioxide as scientists previously believed.
The study, published in the journal Nature, is based on a five-year project known as “B4Warmed,” which simulated the effects of climate change on 10 boreal and temperate tree species growing in an open-air setting in 48 plots in two forests in northern Minnesota. Scientists measured how much carbon dioxide the artificially warmed plants respired — released into the air via their leaves — and learned that over time, the trees acclimated to warmer temperatures and increased their carbon emissions less than expected.
Researchers increased temperatures at the test plots by 3.4°C — an increase that might happen by the end of the 21st century — and learned that plants grown and measured at those higher temperatures increased their leaf respiration by an average of 5% compared to plants in ambient temperatures. Had the juvenile plants not been acclimated to the higher temperatures, their respiration would have increased by 23% versus the plants in ambient temperatures, the university said.
The findings are important to climate change research because prior research with tiny plants in laboratory settings found that warming over a period of weeks accelerated plants’ release of carbon much more than the Minnesota team found in the more realistic long-term forest experiment, which measured change from 2009 through 2013 and considered both experimental and seasonal temperature variations.
“This work is important because most global carbon cycle models ignore this respiratory adjustment and project accelerated climate warming because of elevated respiratory carbon dioxide release. Now, with better data, we can make those models more realistic,” said University of Minnesota professor of forest resources Peter Reich, who led the project and is the paper’s lead author.
“Although these results are ‘good news’ in the sense that the underlying physiology of plants is not going to make the warming of the planet radically worse, the problem we have created in the first place with our greenhouse gas emissions from fossil fuel burning still exists,” he added. “So, we very much still need to cut our carbon emissions in the coming decades by enough to stop climate change.”
B4Warmed was funded primarily by the U.S. Department of Energy. The research team included scientists from the University of Minnesota as well as institutions in China and Maryland.