Study reveals climate change leads to the release of underground carbon stocks

Topsoil is the largest store of carbon, as well as one of the most important sources of carbon dioxide in the atmosphere. Global warming accelerates the decomposition of humus in the soil. It also affects the waxy and woody compounds that help plants store carbon in their leaves and roots and were previously thought to be stable. These are the results of a study conducted by researchers from the Department of Geography at the University of Zurich in the Sierra Nevada National Forest.

The work has been published in the journal Natural Earth Sciences.

About a quarter of the world’s carbon emissions are sequestered by forests, grasslands and grasslands. Plants use photosynthesis to store carbon in their cell walls and in the soil. About half of the carbon in soil is found in layers deeper than 20 cm deep. But even these lower layers are getting warmer due to climate change.

Loss of vital carbon sinks

Rising temperatures cause a significant loss of organic compounds that help plants store carbon in their leaves and roots. Previously, scientists assumed that complex polymers, which have a more stable molecular structure, are able to withstand natural decomposition for a longer period and thus store carbon in the soil.

However, the UZH-led study has now shown that the compound lignin, which gives plants toughness, decreased by 17%, while waxy compounds called cutin and subrin, which protect plants from pathogens and are found in leaves, stems and roots, decreased by 30%. Even pyrogenic carbon, the organic compound that remains after wildfires, was present in greatly reduced amounts.

The experiments were conducted in the Sierra Nevada forests in California. Soils 1 m deep were artificially heated by 4 °C over a period of 4.5 years, following daily and seasonal cycles. This amount of warming is consistent with projections through the end of the century in the business-as-usual climate scenario.

Consequences of using soil to address global warming

These results are of great importance for one of the main strategies in combating global warming, which is to rely on soils and forests as natural carbon sinks. As part of this strategy, crop plants with deep roots and cork-rich biomass are developed. “Until now it was assumed that this would keep the carbon dioxide out₂ Trapped in the ground, says Michael W. Schmidt, a professor of geography and recent author of the study.

“But our results show that all components of soil humus will decline at the same rate, simple chemical compounds and polymers alike. If these initial observations are confirmed in long-term field trials, the consequences are alarming.” If the forest floor loses humus on a large scale thus carbon is released in the form of carbon dioxide₂The pace of global warming will accelerate further. “Our goal should be to stop emissions at source,” says Schmidt.