Soil microbes are responsible for the decomposition of organic matter in the soil, which releases carbon dioxide (CO2) into the atmosphere. This process, known as heterotrophic respiration, is a significant contributor to atmospheric CO2 concentration. A new study published in the scientific journal Nature Communications shows that CO2 emissions from soil microbes are expected to increase by up to 40% by the end of the century, with the most significant increase occurring in the polar regions.
The Novel Mathematical Model
The study was conducted by a team of researchers from ETH Zurich, the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, the Swiss Federal Institute of Aquatic Science and Technology Eawag, and the University of Lausanne. They developed a novel mathematical model that estimates CO2 emissions from soil microbes based on only two environmental factors: soil moisture and soil temperature. The model encompasses all biophysically relevant levels, ranging from soil structure to global ecosystems.
The model is significant because it simplifies the estimation process and enhances our understanding of how heterotrophic respiration in diverse climate regions contributes to global warming. According to Peter Molnar, a professor at the ETH Institute of Environmental Engineering, the model complements large Earth System models and allows for a more straightforward estimation of microbial respiration rates.
CO2 Emissions in Polar Regions
The study found that the increase in microbial CO2 emissions varies across climate zones. In cold polar regions, the decline in soil moisture is the primary contributor to the increase, rather than a significant rise in temperature, unlike in hot and temperate zones. Even a slight change in water content can lead to a substantial alteration in the respiration rate in the polar regions.
Under the worst-case climate scenario, microbial CO2 emissions in polar regions are projected to rise by ten percent per decade by 2100, twice the rate anticipated for the rest of the world. These conditions prevail during soil thawing in polar regions. On the other hand, soils in other climate zones exhibit a comparatively smaller increase in microbial CO2 emissions.
CO2 Emissions in Different Climate Zones
As of 2021, most CO2 emissions from soil microbes originate from warm regions, with 67% coming from the tropics, 23% from the subtropics, 10% from the temperate zones, and 0.1% from the polar regions. However, the study projects substantial growth in microbial CO2 emissions across all these regions by 2100, with an increase of 119% in the polar regions, 38% in the tropics, 40% in the subtropics, and 48% in the temperate zones.
The carbon balance in soils, determining whether soils act as a carbon source or sink, depends on the interplay between photosynthesis and respiration. Therefore, studying microbial CO2 emissions is essential for comprehending whether soils will store or release CO2 in the future. Due to climate change, the magnitude of carbon fluxes remains uncertain, impacting the current role of soils as carbon sinks.
The study highlights the urgent need for more accurate estimates of heterotrophic respiration rates. The projections of increased CO2 emissions from soil microbes emphasize the need for immediate action to mitigate global warming. The novel mathematical model developed in the study provides a more straightforward estimation of microbial respiration rates based on soil moisture and soil temperature, enhancing our understanding of the carbon dynamics within soil ecosystems.
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