Soil is a big deal when it comes to climate change, and most of the news lately has been bad. Carbon dioxide released by thawing permafrost in the Arctic is likely to accelerate climate change, even if it doesn't reach runaway conditions. Further south, warming soil is expected to release more and more carbon, but on that point there is some good news: New experiments suggest soil-dwelling crustaceans, called isopods, may help limit how much carbon escapes in the the air.
Soil pumps a startlingly large amount of carbon into the air; about 10 times what's released when we burn fossil fuels. But it's a delicate and complicated balance. In forest soils, basidiomycetes—fungi also known as cords for the root-like structures they form underground—release enzymes that stimulate, for example, the growth of other, wood-decomposing fungi. But as the days get hotter, cords thrive, growing more abundant, releasing more enzymes, aiding decomposition, and, ultimately, producing more carbon dioxide.
It's a major worry, given that forest soils alone contain around 800 trillion kilograms of carbon, about 60 trillion kilograms of which is released every year. But that worry may stem in part from an incomplete picture of soil ecosystems, argues an international team of researchers led by Thomas Crowther, a postdoctoral associate at Yale University's School of Forestry and Environmental Studies.
Isopods can help counteract the effects of rising temperatures on the carbon stored in the world's forest soils.
In particular, Crowther and his team reasoned, if climate change increases the number of cords lying around, it may also increase the number of isopods—half-inch-long crustaceans otherwise known as pill bugs—that eat them. In other words, nature might have a Plan B for limiting cord growth and keeping carbon in the ground.
To test that idea, the researchers conducted a series of experiments at the Harvard Forest Long-Term Ecological Research site in north-central Massachusetts. There, the team set up forest soil samples in chambers at two different temperatures and with two levels of nitrogen concentration (increased nitrogen from agricultural runoff is another factor likely to drive cord growth). In addition, the team removed isopods, cords, or both from some samples to examine their effects on soil ecosystems.
After 90 days, the team opened up the chambers and measured the total amount of fungal biomass inside, including cords and other fungi. Warmer temperatures, added nitrogen, and the presence of basidiomycetes all worked to increase fungal biomass—and, more importantly, wood-decomposing fungi that contribute to carbon dioxide emissions.
But in soil samples with both cords and isopods, the team found, the mass of fungus matched that of control samples in which there were neither cords nor isopods. Wood decomposition rates also slowed; apparently, isopods can help counteract the effects of rising temperatures on the carbon stored in the world's forest soils.
That's not to say that isopods can halt climate change. But, the researchers argue today in Proceedings of the National Academy of Science, it might help dampen one source of further warming—a fact they hope their peers will consider in future climate projections.
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