A study examining the impact of rising temperatures on soil has shown that warming alone does not increase carbon dioxide emissions from the soil. A significant rise in CO₂ emissions is observed only when higher temperatures coincide with an increase in easily accessible forms of carbon and nutrients such as nitrogen and phosphorus.

The Role of Microbes in Carbon Dioxide Emissions

The findings offer new insights into how nature maintains the delicate balance between carbon accumulation in soil and its release into the atmosphere. A large portion of soil CO₂ emissions is linked to the activity of microbes—bacteria, fungi, viruses, and other microorganisms—that, much like humans, "exhale" carbon dioxide. As explained by Debjani Sihi, Associate Professor in the Department of Plant and Microbial Biology at the University of North Carolina, warming enhances plant photosynthesis, which increases the amount of "food" available to microbes and, consequently, their activity. However, if the soil lacks accessible forms of carbon and essential nutrients needed for microbial growth and survival, higher temperatures alone do not lead to increased carbon loss.

Sihi also notes that simply adding heat and nutrients did not increase CO₂ emissions from the studied soil, which was collected from a long-term experimental site in the southeastern United States. For emissions to rise, the presence of easily digestible forms of soil carbon was necessary.

Research Features

Previous experiments of this kind were mostly conducted in cold climates—arctic, boreal, or temperate—to understand how slight warming might cause significant changes. In contrast, this study was carried out on nutrient-poor subtropical soil in Athens, Georgia, home to one of the world’s oldest soil warming facilities. The research took place on former cotton fields that have since become forested. Cotton is a crop that depletes soil, resulting in low levels of nutrients and carbon.

Scientists collected soil from the experimental site and brought it to the lab, where it was heated by 2.5°C. They also studied various pathways in the soil carbon cycle—a process in which carbon is either stored in the soil or released from it. Soil contains many forms of organic matter, from plant residues to living and dead microbes, all of which participate in the carbon cycle. Microorganisms are constantly searching for food to survive and grow, and the researchers tracked how much carbon is stored in different pools.

How Microbes Use Carbon

Microbes respire and obtain energy from carbon, as well as fulfill their nutritional needs from the same food source. Like humans, they require a balanced diet—energy sources, proteins, and fiber. Some of the carbon is used to build biomass, some energy is spent on producing enzymes needed to break down complex organic matter into absorbable forms of carbon and nutrients. The rest is released as CO₂ as part of their metabolism.

The Balance Between Carbon Release and Absorption

Nature not only releases carbon but also absorbs it. Understanding how much CO₂ is emitted from natural systems helps set targets for reducing emissions across various industries and economic sectors.

Future Research Prospects

Sihi points out that collaborative research continues to study different ecosystems, including two field soil warming experiments in the tropics—in Puerto Rico and Panama. This is essential for understanding how warming affects soil carbon loss. According to her, in these conditions, warming alone does not stimulate microbial activity because microbes simply lack the resources needed for life. Thus, depleted microbial resources limit the effect of warming.