The Real Dirt

Earthworms are on the rise around the world. And that’s not good news for the fight against climate change: According to a new study, earthworms make the soil release more greenhouse gases.

Partly because of agricultural practices, “earthworm presence is likely to increase in ecosystems worldwide,” the study authors write in Nature Climate Change. For example, organic fertilizer helps feed earthworms, and the decline of tillage allows earthworms to flourish. Exotic worm species, spread by humans, also are invading new territory in North America.

Scientists haven’t been sure how earthworms affect greenhouse-gas emissions from soil. Worms eat plant litter and burrow through the dirt, which can increase carbon dioxide (CO2) and nitrous oxide (N2O) emissions. But they also might help carbon stay in the soil, which would cut CO2 emissions.

The researchers reviewed 57 studies on earthworms, covering 237 observations. Overall, earthworms do increase greenhouse-gas emissions, the team found. When soil contains earthworms, CO2 and N2O emissions go up by 33 percent and 42 percent, respectively.

Earthworms also may help plants grow, and plants suck up CO2. But that might not be enough to cancel out the effects of the greenhouse-gas emissions, the authors say. Roberta Kwok | 8 February 2013

Source: Lubbers, I.M. et al. 2013. Greenhouse-gas emissions from soils increased by earthworms. Nature Climate Change doi: 10.1038/nclimate1692.

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