Feedback loops exacerbate climate change, a study makes clear again: The CO2 emissions of soil microbes are increased enormously by the consequences of climate change, researchers report. This emerges from new model calculations that shed more light on this effect and its mechanisms. Accordingly, a global increase in microbial soil respiration of up to 40 percent can be expected by the end of the century. The arctic areas are growing particularly strongly. In contrast to the rest of the world, the main reason for the increase in emissions is not the rise in temperature, but the increasing humidity, the scientists explain.
It is well known that humans are the last straw - but the contributions of natural systems must also be taken into account when calculating the global CO2 balance. A major factor here is soil respiration: a significant proportion of the greenhouse gases in the atmosphere are due to the activity of microorganisms such as bacteria, fungi and other microorganisms, which decompose organic material in the soil with the help of oxygen. In the context of the climate crisis, this so-called heterotrophic soil respiration has long been a concern. Because it is becoming apparent that the consequences of climate change are increasing the microbial degradation of biomass underground. However, the actual extent of the problem has so far been difficult to assess.
Key factors: temperature and soil moisture
That is why the researchers led by Alon Nissan from the Swiss Federal Institute of Technology in Zurich have now developed a new mathematical model. As the team explains, the forecast is based in an innovative way on two key factors that significantly shape the extent of soil respiration: soil moisture and soil temperature. The advance of the approach also lies in the fact that the model includes all biophysically relevant levels with a global perspective - from the micro level of soil composition and water distribution in the soil to plant communities such as forests, entire ecosystems and climate zones. "In addition, simulations, laboratory measurements and field observations validate the new approach," write the scientists.
As they report, their calculations initially revealed the following: Since the 1980s, heterotrophic respiration has been increasing worldwide at a rate of around two percent per decade. In turn, the projections indicate that CO2 release from soil microbes will increase at an accelerating rate through the end of this century. In the worst case, there is a risk of a global increase of up to around forty percent compared to today's values. In addition to this overall view, an important aspect of the study is that it now becomes clear how differently strong and differently justified the increase will be in the different climate zones. Above all, the relatively small share of the Arctic regions in the total emissions will increase sharply. Because for these areas, the model calculations even predict growth of more than double.
Strong growth with regional peculiarities
As the scientists explain, the increasing soil moisture has an effect there and less the temperature rise as in the warm and temperate zones. "Even a small change in water content can lead to a significant change in respiration intensity in the polar regions," says Nissan. Because, as he explains, when the soil thaws, optimal moisture conditions are created for the activity of the microorganisms - it is neither too wet nor too dry. Although, according to the calculations, microbial CO2 emissions will also increase significantly in the other climate zones, the increase will be less than in the north because the soil there is comparatively dry, the researchers explain.
"So the increase in microbial CO2 emissions that we are predicting will further contribute to exacerbating global warming," Nissan concludes. Because of the great importance in the context of the earth's climate system, he and his colleagues want to devote themselves to the topic in more detail. In addition to heterotrophic respiration, autotrophic respiration will also be discussed. This is the ability of plant roots to breathe in the soil. "Further research into these factors could enable a more comprehensive understanding of carbon dynamics in soil ecosystems," the scientists hope.
Source: Swiss Federal Institute of Technology in Zurich, specialist article: Nature Communications, doi:10.1038/s41467-023-38981-w