Bad news: Trees emit methane, a greenhouse gas. Good news: Some are home to bacteria that can’t get enough of it.
MANY OF TODAY’S geoscientists are carbon voyeurs. Knowing that human disregard for the carbon cycle has screwed the climate, they have kept a close eye on carbon’s hottest variants—carbon dioxide (CO 2) and methane. Both gasses trap heat on the planet through the greenhouse effect, and over a span of 100 years methane is 28 times more potent than CO2. Rigorously accounting for greenhouse gas flow is step one of building models that predict the future climate.
Some line items in the methane budget, such as pipeline leaks and cow farts, are well understood. But others are hazier. “There’s lots of gaps and uncertainties, particularly in wetlands, and inland waters,” says Luke Jeffrey, a biogeochemistry postdoc at Southern Cross University in Australia. By one 2020 tally from the Global Carbon Project, wetlands emit about 20 to 31 percent of Earth’s annual methane release—more than the amount from fossil fuel production.
But in the past decade, researchers have zeroed in on a perhaps counterintuitive source of greenhouse gas emissions: trees. Freshwater wetland trees, in particular. Trees bathing in wet or flooded soil absorb methane and then leak it through their bark. In a 2017 study, ecologist Sunitha Pangala, then at the Open University in the United Kingdom, found that trees in the Amazon were responsible for 200 times more methane than trees in other wetland forests, accounting for 44 to 65 percent of the region’s total emissions.
Does this mean trees are bad for the planet? Of course not. Trees suck carbon dioxide out of the atmosphere. And in a study published April 9 in Nature Communications, Jeffrey and his team report how trees can also be methane sinks, sheltering microbes that convert it to the less damaging CO2.