Plants will adapt to global warming, pump out less carbon

While we sweat it out, plants will cope better with climate change than first thought, a pair of studies revealed.

Research published this week has shown that trees will contribute less carbon to our atmosphere as a result of climate change, while another study gave plants a more positive prognosis in the face of climbing temperatures.

Trees have long been considered a contributor to the future warming of our planet. Although plants inhale carbon dioxide from the air during photosynthesis during the day, they also breathe a lot out at night.

This respiration process happens on a huge scale: plants across the world blow out around 60 billion tons of carbon dioxide every year. That’s about six times that produced by humans burning fossil fuels.

And as the air gets warmer, trees breathe deeper, increasing their carbon emissions. Climate models previously assumed that if the temperature doubles, tree respiration will also double. But a new study, undertaken by an international research group and published this week in the Proceedings of the National Academy of Sciences, suggests the increase could be less dramatic.

“What we thought was a steep curve in some places is actually a little gentler,” says Kevin Griffin, a plant physiologist at Columbia University and co-author of the study. “With this new model, we predict that some ecosystems are releasing a lot less carbon dioxide through leaf respiration than we previously thought.”

To uncover the figures, researchers subjected leaves to heat and analysed the results in different climates and conditions around the world. Test sites included Alaskan tundra, boreal forests in Sweden, tropical areas in Peru and savannahs in Texas and Australia.

The world’s carbon cycle is incredibly complex, and the researchers say a decrease in carbon output in one system can cause increases elsewhere.

The findings suggest that although trees quickly respond to warmer temperatures with increased carbon exhalation, they also eventually acclimatise, and their rapid response tapers off.

Trees in colder climates were particularly quick to steady their increased respiration. For example, the results suggest that long-term responses from trees on the North Slope of Alaska are 28% lower than the current estimates.

“All of this adds up to a significant amount of carbon, so we think it’s worth paying attention to,” says Griffin.

Another study, published last week in the journal Nature, suggests that plants are also better at acclimatising their respiration to warmer temperatures than previously thought.

Led by Peter Reich at the University of Minnesota, the study measured North American forest trees in increasing temperatures over a five-year period.

The findings show that because the trees begin to acclimatise, their respiration increased by only 5%, compared with an expected increase of 23%, reducing their long-term carbon output significantly.

Mary Heskel of Massachusetts’ Marine Biological Laboratory, and lead author of the global tree study, says the findings released this week have important consequences.

But the world’s carbon cycle is incredibly complex, and the researchers say a decrease in carbon output in one system can cause increases elsewhere.

“We now have a better way to estimate one process, but it’s only one process,” Griffin explains.

“The whole system is quite complicated, and a small change in the balance between one part and another could produce a really big result. That’s the challenge we face when we think about the earth as a whole.”