Global Warming Accelerates CO2 Emissions from Soil Microbes

The scanning electron microscope image shows a colony of bacteria (coloured bluish) around a few micrometres small root (brown) in the soil. Credit: Nissan A. et al., Nature Communications, 2023

Key points:

• A new model shows emissions of CO₂ by soil microbes will increase by up to 40% by 2100.
• The growth it primarily fueled by the warm regions of the Earth.
• Scientists are now exploring CO₂ emissions through autotrophic respiration for a more comprehensive picture.

New research by scientists at ETH Zurich indicates that emissions of CO₂ by soil microbes into the Earth's atmosphere are not only expected to increase but also accelerate on a global scale by the end of this century. The scientists say the increase could reach up to about 40% globally, compared with the current levels, under the worst-​case climate scenario.

For the study, published in Nature Communications, ETH postdoctoral fellow Alon Nissan developed a new mathematical model that simplifies the estimation process by utilizing only two crucial environmental factors: soil moisture and soil temperature. The model represents a significant advancement as it encompasses all biophysically relevant levels, ranging from the micro-​scales of soil structure and soil water distribution to plant communities like forests, entire ecosystems, climatic zones, and even the global scale.

As of 2021, most CO₂ emissions from soil microbes are primarily originating from the warm regions of the Earth. Specifically, 67% of these emissions come from the tropics, 23% from the subtropics, 10%from the temperate zones, and a mere 0.1% from the arctic or polar regions.

According to the study, substantial growth is expected to occur in microbial CO₂ emissions across all these regions compared with the levels observed in 2021. By the year 2100, projections indicate an increase of 119% in the polar regions, 38% in the tropics, 40% in the subtropics and 48% in the temperate zones.

Even irrespective of the climate zone, the influence of temperature remains consistent: as soil temperature rises, so does the emission of microbial CO₂.

In their ongoing study, the researchers have primarily focused on heterotrophic respiration. However, they have not yet investigated the CO₂ emissions that plants release through autotrophic respiration. They say further exploration of these factors will provide a more comprehensive understanding of the carbon dynamics within soil ecosystems.