Chapter 2 explains that “Soils are the largest terrestrial reservoir of organic carbon” and that soil organic matter is formed from dead plant and animal material that is decomposed by microorganisms and fauna. It notes that microbial decomposition results in “mineralisation of organic carbon to CO2,” returning carbon to the atmosphere, while some carbon is stabilized in soil as more resistant organic matter. The report highlights that changes in temperature and moisture affect decomposition rates and thus “the balance between soil carbon storage and CO2 emissions.”

Microbes are critical in the process of breaking down and transforming dead organic material into forms that can be reused by other organisms. This is why the soil is such a large reservoir of organic carbon on Earth. ... First, microbes decompose organic carbon and either release it to the atmosphere as CO2 or CH4 or store it in microbial biomass or necromass, contributing to soil organic matter.

The paper describes organic matter decomposition as a biochemical process in which “Once decomposition begins, C is lost as CO2 or sequestered into more recalcitrant carbon difficult to further degradation.” It further states: “As microbial respiration releases carbon dioxide into the atmosphere, microbes act as gatekeepers in the whole process.” The authors emphasize that microbial activities are a major component of the global carbon cycle, controlling whether carbon is released as CO2 or retained in more stable soil carbon pools.

The Department of Energy explains that in the carbon cycle “Plants absorb carbon dioxide during photosynthesis and much of this carbon dioxide is then stored in roots, permafrost, grasslands, and forests. Plants and the soil then release carbon dioxide when they decay.” It notes that “Other organisms also release carbon dioxide as they live and die. For example, animals exhale carbon dioxide when they breathe and release carbon dioxide when they decompose.” This describes decomposers returning carbon from dead organisms to the atmosphere and soil.

The article states that in terrestrial ecosystems, “Microorganisms are central to this process, mediating the decomposition of organic matter and the transformation of carbon compounds. In terrestrial ecosystems, bacteria and fungi break down plant biomass, converting it into simpler organic molecules that can be reused by other organisms.” It adds: “This decomposition releases CO2 into the atmosphere, a process known as respiration.” The paper also notes that when microbes break down organic matter, they can “either mineralize it into CO2, contributing to atmospheric carbon levels, or stabilize it in the form of humus, a process that locks carbon into the soil.”

The overview states: “Decomposers are essential organisms that break down dead organic matter, playing a crucial role in recycling nutrients within ecosystems.” It further explains: “By converting organic matter back into inorganic substances, decomposers release nutrients like carbon and nitrogen into the soil, air, and water, making them available for new growth.” Another section notes that without decomposers, “their elements, including carbon and nitrogen, would be locked inside them. Decomposition makes the nutrients available for other organisms, releasing them into the air, soil, and water.”

Decomposers also release organic compounds and carbon dioxide when they break down dead organisms and waste products. Carbon can cycle quickly through this pathway, especially in aquatic ecosystems, where tiny phytoplankton decompose rapidly or are consumed by other organisms.

Carbon is stored on our planet in the following major sinks (1) as organic molecules in living and dead organisms found in the biosphere; (2) as the gas carbon dioxide in the atmosphere; (3) as organic matter in soils; (4) in the lithosphere as fossil fuels and sedimentary rock deposits such as limestone, dolomite and chalk; and (5) in the oceans as dissolved atmospheric carbon dioxide and as calcium carbonate shells in marine organisms. ... The detritus food chain contains a number of decomposers (fungi and bacteria) whose primary ecological role is the decomposition of organic matter into its raw materials. Carbon is released from ecosystems as carbon dioxide gas by the process of respiration.

This explainer notes that soil microbes “decompose organic matter like plant litter and dead organisms, and create simple carbon compounds.” It continues: “The simple carbon compounds can then be used by other organisms, or turned into gases -- like carbon dioxide -- and released into the atmosphere.” The research summarized shows that when conditions favor microbial activity, “faster decomposition of leaf litter” leads to “the release of larger amounts of carbon dioxide,” illustrating decomposers returning carbon from dead biomass to the atmosphere.

Describing decomposers in the carbon cycle, the article notes: “In the carbon cycle, decomposers break down dead material from plants and other organisms and release carbon dioxide into the air.” It also explains that decomposers “help move carbon and other elements from dead organisms back into the environment, where they can be reused by living things.” This ties decomposition to the return of carbon to both ecosystems and the atmosphere.

Decomposers are organisms, such as bacteria and fungi, that break down dead or decaying organisms. They play a crucial role in the carbon cycle by decomposing dead organisms and waste products, releasing carbon dioxide back into the atmosphere through the process of respiration, and returning nutrients to the soil.

Decomposers are organisms that break down dead plants and animals into simpler substances. Through this process of decomposition, nutrients, including carbon, are returned to the soil, air, and water, where they can be used again by other organisms.

The module explains: “Carbon dioxide is added to the atmosphere naturally when organisms respire or decompose (decay)… When organisms die, they are decomposed by bacteria. Carbon dioxide is released into the atmosphere or water during the decomposition process.” It further clarifies that respiration is “also the process by which once-living (organic) organisms are decomposed,” explicitly linking decomposition of dead organisms to CO2 release and thus return of carbon to the atmosphere.

This educational article explains that dead plant and animal material becomes soil organic matter: “As plants and animals die, their residues are added to soils, where they are decomposed by soil organisms.” It notes that some of this carbon is “rapidly decomposed and released as CO2 to the atmosphere through microbial respiration,” while some becomes more stable humus that “can remain in soils for decades to millennia.” Thus, the activity of soil decomposers both returns carbon to the atmosphere and contributes to carbon stored in soils.

When plants and animals die, their tissues decompose. Decomposers break down the organic matter, releasing carbon dioxide to the atmosphere through respiration and leaving some organic carbon in the soil as humus. In this way, soils act both as a source and a sink of carbon in the global carbon cycle.

CK-12 describes decomposers as organisms that “break down dead organisms and other organic wastes.” It notes that in doing so, “decomposers return nutrients, including carbon, to the soil or water where they can be used again by producers.” It also states that as decomposers respire, “carbon dioxide is released back into the atmosphere,” linking decomposition to both soil nutrient return and atmospheric CO2.

In ecology, decomposers (primarily bacteria and fungi) are defined as organisms that break down dead plants and animals and their wastes, converting complex organic compounds into simpler substances. In the carbon cycle, this process releases part of the carbon as carbon dioxide (and sometimes methane under anaerobic conditions), which returns to the atmosphere, while the remaining carbon contributes to soil organic matter, thereby returning and storing carbon in soils.

The video explains that “decomposers recycle nutrients from dead plant or animal matter back to the soil in terrestrial environments or to the water in aquatic environments.” Later it notes that “decomposers break those things down into smaller parts like nutrients and other chemicals… those chemicals go down into the ground and are taken up by plants.” While focused on nutrients generally, the context is that atoms, including carbon, are cycled between living organisms and the nonliving environment.

When organisms die or produce wastes, decomposers like bacteria and fungi break down the carbon compounds that are present in the dead bodies or wastes. This also returns carbon dioxide to the atmosphere since decomposers are doing respiration with much of the material that they are decomposing. ... Notice that carbon moves from the atmosphere to living things through photosynthesis, and that carbon gets returned to the atmosphere by respiration, decomposition, and combustion.