Unexpected helpers discovered in the carbon cycle


Even small, soil-dwelling invertebrates like this springtail break down cellulose. © Andy Murray, chaosofdelight.org

Plants not only beautify our environment visually, they also absorb large amounts of CO2 from the air and store it in their tissue. But what happens to the CO2when a plant dies? Until now, it was thought that only soil microbes and fungi decompose the plant tissue and thereby release the CO2 release again, but apparently other, unexpected helpers are involved, as biologists have now discovered.

Carbon dioxide does not have the best reputation due to its climate-warming greenhouse gas function. But the carbon it contains is not only found in the atmosphere, but also in water, rock, soil and even in our own bodies. In the carbon cycle, the element moves back and forth between these different spheres and takes on different forms. For example, plants absorb CO2 from the air and use it as a building block for the cellulose in their tissue. When the plants die, microorganisms in the soil decompose the cellulose and other organic substances and release CO2 into the atmosphere.

On the trail of soil animals

But breaking down cellulose is not such an easy task. It requires powerful tools in the form of certain enzymes that split polysaccharides. So far, these have been found mainly in bacteria and fungi, which is why these organisms were considered to be the main decomposers in the soil. But that could be too short-sighted, as researchers led by Hannah Mülbaier from Goethe University in Frankfurt am Main have now discovered.

For the first time, the team also investigated the role of other soil-dwelling microorganisms in the degradation of long-chain organic sugar compounds: soil invertebrates such as springtails and oribatid mites. To find out whether the soil animals are also capable of decomposing cellulose, Mülbaier and her team carried out detailed genome analyses on over 200 different species of springtails and oribatid mites, specifically looking for genes for cellulose degradation.

Oribatid mite
Oribatid mites also play an important, previously overlooked role in the carbon cycle. © Andy Murray, chaosofdelight.org

Long overlooked helpers of the carbon cycle

And indeed, the majority of the soil animals examined carry the blueprint for cellulose-degrading enzymes in their genome, as the researchers report. Overall, they found this genetic code in three of the four known main lines of springtails as well as in almost all original groups of oribatid mites. “When comparing the genomes, we also found that the ability to decompose cellulose was acquired early in the evolutionary history of the species. The soil invertebrates have therefore probably been helping to decompose plant remains for a long time, either alone or in cooperation with fungi or bacteria that live in their intestines,” explains senior author Miklós Bálint from the LOEWE Center for Translational Biodiversity Genomics in Frankfurt am Main.

The new findings also have an impact on our understanding of the carbon cycle: “Until now, little was known about the contribution of animals to this decomposition process – beyond purely mechanical shredding. Our results now provide an indication that soil invertebrates such as springtails and oribatid mites play an important, previously overlooked role in the carbon cycle of soils, given their widespread occurrence worldwide,” says Bálint. Since soil invertebrates react differently to environmental changes than microorganisms and fungi, previous predictions about how the carbon cycle will change due to climate change may now have to be revised.

Source: Senckenberg Society for Natural Research; Article: Molecular Ecology, doi: 10.1111/mec.17351

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