Rising CO2 levels might not be as good for plants as we thought

Two major groups of plants have shown a surprising reversal of fortunes in the face of rising levels of carbon dioxide in the atmosphere.

During a 20-year field experiment in Minnesota, a widespread group of plants that initially grew faster when fed more CO₂  stopped doing so after 12 years, researchers report in the April 20 Science. Meanwhile, the extra CO₂ began to stimulate the growth of a less common group of plants that includes many grasses. This switcheroo, if it holds true elsewhere, suggests that in the future the majority of Earth’s plants might not soak up as much of the greenhouse gas as previously expected, while some grasslands might take up more.

“We need to be less sure about what land ecosystems will do and what we expect in the future,” says ecosystem ecologist Peter Reich of the University of Minnesota in St. Paul, who led the study. Today, land plants scrub about a third of the CO₂ that humans emit into the air. “We need to be more worried,” he says, about whether that trend continues.