Climate change is affecting not only the surface of the Earth, but also its depths.
A new study by researchers from the University of Zurich has revealed that global warming is accelerating the decomposition of organic matter in subsoils, which are the largest storehouses for carbon on land.
This could have serious implications for the carbon cycle and the climate system, as more carbon dioxide is released into the atmosphere.
How climate change affects soil carbon
Ezra Acayan/Getty Images
Soil contains about three times more carbon than the atmosphere and the vegetation combined. About half of this carbon is stored in subsoils, which are deeper than 20 centimeters, as per Phys.org.
Subsoils are rich in organic matter, such as hummus, lignin, cutin, suberin, and pyrogenic carbon.
These compounds are derived from plants and microbes and have different degrees of stability and resistance to decomposition.
Previous studies have shown that climate change can increase the temperature and moisture of subsoils, which can enhance microbial activity and the breakdown of organic matter.
However, it was unclear how this would affect the different types of organic compounds, and whether some of them would be more resilient than others.
To address this question, the researchers conducted a field experiment in the Sierra Nevada National Forest in California.
They artificially heated up a one-meter-deep soil by 4°C for 4.5 years, following daily and seasonal cycles.
This amount of warming is consistent with projections for the end of the century under a business-as-usual scenario.
They then measured the changes in the concentration and composition of organic matter in the soil.
The researchers found that warming caused a significant loss of all types of organic compounds in subsoils, regardless of their stability or complexity.
For example, lignin, which is a woody compound that gives plants their stiffness, was reduced by 17%, as per Eurekalert.
Cutin and suberin, which are waxy compounds that protect plants from pathogens and water loss, were down 30%; ehile pyrogenic carbon, which is produced by fire and has a very stable structure, was also decreased.
The researchers estimated that warming increased the decomposition rate of organic matter in subsoils by 37%.
This means that more carbon dioxide was released from subsoils to the atmosphere, potentially creating a positive feedback loop that could amplify global warming.
The researchers also compared their results with measurements from other studies across different regions and climates.
They found that their findings were consistent with a global pattern of increased decomposition of organic matter in subsoils due to warming.
The implications: rethinking soil management
The study has important implications for our understanding and management of soil carbon.
It challenges the assumption that some organic compounds are more resistant to decomposition than others and that they can act as long-term carbon sinks in subsoils.
It also suggests that relying on soils and forests as natural carbon sequestration strategies may not be as effective as expected.
The researchers call for more research to understand the mechanisms and consequences of subsoil warming and decomposition.
They also urge for more actions to reduce greenhouse gas emissions and prevent further soil degradation.
