Is the earthworm turning into a global warming saviour? Earlier this year, the animals were cast as key contributors to climate change, but they may have been falsely accused.
A fifth of carbon dioxide emissions come from soils, and earthworms play a central role. They churn up soil, encouraging breakdown of organic matter to produce CO2. They also drive subterranean processes that both lock up and release carbon.
A recent review of more than 200 published studies by Ingrid Lubbers of Wageningen University in the Netherlands and colleagues concluded that worms increase CO2 emissions from soils by a third on average.
Weixin Zhang of the South China Botanical Garden in Guangzhou says things are more complex. His team's work shows that microbes in the guts of earthworms convert organic carbon into a form that can be stored in soils.
"We believe the recent estimation of earthworms increasing soil emissions by 33 per cent is likely a severe overestimate," says Zhang.
Most studies have been too short to spot this gut-microbe effect, Zhang says. You have to watch for years to see it. Right now, no long-term measurements have actually been done, agrees Lubbers.
The findings could be important in future assessments of climate change – especially as the worms spread to new regions. Earthworms did not figure at all in the latest report on climate science by the Intergovernmental Panel on Climate Change (IPCC).
Dangerous aliens
"Earthworms play an essential part in the greenhouse-gas balance of soils worldwide, and their influence is expected to grow over the next decades," says Lubbers.
For instance, following wipeout during the last ice age, large parts of North America were earthworm-free until Europeans brought soil from home. Old-world earthworms are still migrating north. Some researchers, such as Paul Hendrix of the University of Georgia in Athens, see their presence as a dangerous alien invasion.
Farming, including ecological methods like no-till farming, promotes the spread of earthworms, says Lubbers. And global warming will likely make them more active.
Journal reference: Nature Communications, DOI: 10.1038/ncomms3576
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