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Global warming could accelerate CO2 emissions from soil microbes

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New research published in the scientific journal Nature Communications reveals alarming findings regarding the impact of soil microorganisms on atmospheric CO2 levels. These microorganisms, which play a crucial role in decomposing organic matter in soil, are responsible for releasing CO2 into the atmosphere through a process known as heterotrophic respiration. According to the study conducted by a team of scientists 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, these emissions are projected to rise significantly by the end of the century.

Under the worst-case climate scenario, the researchers estimate that global CO2 emissions from soil microbes could surge by up to 40% by 2100 compared to current levels. This acceleration of CO2 release has particularly grave implications for the polar regions. Alon Nissan, the lead author of the study and an ETH Postdoctoral Fellow at the ETH Zurich Institute of Environmental Engineering, emphasizes the urgent need for more accurate estimations of heterotrophic respiration rates in order to address the worsening of global warming caused by these microbial emissions.

In summary, the study highlights the concerning prospect of increasing CO2 emissions from soil microbes, exacerbating the already critical issue of rising atmospheric CO2 concentrations. Urgent action is required to better understand and mitigate the effects of heterotrophic respiration on global warming.

Soil moisture and temperature as key factors

The recent findings not only confirm previous research but also provide a more precise understanding of the mechanisms and extent of heterotrophic soil respiration in various climate zones. Unlike previous models that rely on multiple parameters, the innovative mathematical model developed by Alon Nissan simplifies the estimation process by focusing on two critical environmental factors: soil moisture and soil temperature.

This model represents a significant breakthrough as it incorporates all biophysically relevant levels, ranging from the microscopic scale of soil structure and water distribution to larger scales such as plant communities, ecosystems, climatic zones, and even the global scale.

Professor Peter Molnar from the ETH Institute of Environmental Engineering emphasizes the importance of this theoretical model, which complements existing Earth System models. He explains that the model enables a more straightforward estimation of microbial respiration rates based on soil moisture and temperature. Furthermore, it enhances our understanding of how heterotrophic respiration in different climate regions contributes to the issue of global warming.

In summary, the novel mathematical model developed by Alon Nissan not only provides more accurate insights into heterotrophic soil respiration but also offers a simplified approach to estimating microbial respiration rates based on crucial environmental factors. Its comprehensive scope contributes to our understanding of the role played by heterotrophic respiration in various climate zones and its implications for global warming.

Polar CO2 emissions likely to more than double

One of the key findings from the collaborative research led by Peter Molnar and Alon Nissan is the variation in the increase of microbial CO2 emissions across different climate zones. In polar regions, the primary driver of the increase is the decline in soil moisture rather than a significant temperature rise, as observed in hotter and temperate zones. Alon Nissan emphasizes the sensitivity of cold regions, noting that even a slight change in water content can have a substantial impact on the respiration rate.

According to their calculations, under the worst-case climate scenario, polar regions are expected to experience a ten percent per decade increase in microbial CO2 emissions by 2100, which is twice the rate projected for the rest of the world. This disparity can be attributed to the optimal conditions for heterotrophic respiration, which occur when soils are semi-saturated, neither too dry nor too wet. These conditions are prevalent during soil thawing in polar regions.

Conversely, in other climate zones where soils are already relatively dry and prone to further desiccation, the increase in microbial CO2 emissions is relatively smaller. However, regardless of the climate zone, the influence of temperature remains consistent: as soil temperature increases, so does the emission of microbial CO2.

In summary, the research highlights that the increase in microbial CO2 emissions varies across climate zones, with polar regions being particularly sensitive due to changes in soil moisture. While temperature plays a significant role in all regions, the impact of soil moisture is more pronounced in cold zones. These findings contribute to our understanding of the complex dynamics of heterotrophic respiration and its implications for climate change.

How much CO2 emissions will increase by each climate zone

As of 2021, the majority of CO2 emissions from soil microbes are predominantly generated in the warmer regions of the world. Specifically, the tropics contribute to 67% of these emissions, followed by the subtropics at 23%, temperate zones at 10%, and the arctic or polar regions accounting for a mere 0.1%.

However, the research conducted by the team suggests that there will be substantial growth in microbial CO2 emissions across all these regions compared to the levels observed in 2021. Projections indicate that by the year 2100, there will be a notable increase in emissions. The polar regions are expected to experience a staggering 119% increase, the tropics a 38% increase, the subtropics a 40% increase, and the temperate zones a 48% increase.

These findings highlight the anticipated rise in microbial CO2 emissions across diverse climate regions, with significant implications for global warming and climate change mitigation efforts.

Will soils be a CO2 sink or a CO2 source for the atmosphere?

The carbon balance in soils is determined by the intricate interplay between two vital processes: photosynthesis, where plants absorb CO2, and respiration, which releases CO2. Understanding microbial CO2 emissions is therefore crucial for determining whether soils will function as carbon sources or sinks in the future.

The impact of climate change on the magnitude of these carbon fluxes, both inflow through photosynthesis and outflow through respiration, remains uncertain. However, this magnitude will have a significant effect on the current role of soils as carbon sinks, as explained by Alon Nissan.

While the researchers have primarily focused on studying heterotrophic respiration in their ongoing study, they have yet to investigate the CO2 emissions resulting from autotrophic respiration by plants. Further exploration of these factors is necessary to gain a more comprehensive understanding of the carbon dynamics within soil ecosystems.

By delving into both microbial and plant respiration processes, scientists can obtain a more complete picture of how soils contribute to the global carbon cycle. This knowledge will aid in refining predictions about future carbon storage and release in the context of ongoing climate change.

Source: ETH Zurich

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