Heterotrophic respiration
Heterotrophic respiration refers to the metabolic processes by which organisms, such as animals, fungi, and various bacteria, convert organic compounds into energy while producing carbon dioxide (CO2) as a byproduct. This process is distinct from autotrophic respiration, where organisms generate their own energy through photosynthesis. Heterotrophic respiration plays a significant role in the carbon cycle and has implications for climate change, as CO2 is a greenhouse gas that can contribute to global warming when present in elevated concentrations in the atmosphere.
The decomposition of organic matter in soil, a key aspect of heterotrophic respiration, is critical because the carbon stored in the top meter of soil is estimated to be twice that in the atmosphere. Activities such as land use changes, including deforestation, can increase CO2 emissions from soil, further influencing climate dynamics. The rate of heterotrophic respiration can also be affected by temperature, with pronounced effects in temperate regions. Various organisms, including macrofauna like earthworms and microscopic bacteria, are involved in this process, with fungi playing a particularly important role in breaking down complex organic materials like cellulose. Understanding heterotrophic respiration is essential for comprehending its impact on global carbon cycles and climate change.
Heterotrophic respiration
Definition
Heterotrophic respiration is a set of metabolic processes through which organisms produce carbon dioxide (CO2) and release energy from organic compounds that they have ingested or otherwise incorporated from outside themselves. It may be differentiated from autotrophic respiration, in which energy-bearing compounds are produced by the organism through processes such as photosynthesis. Heterotrophic organisms include animals, fungi, and many types of bacteria.
Significance for Climate Change
CO2 is a greenhouse gas (GHG), meaning that its increased atmospheric concentration may trap more heat on Earth and raise global temperatures. The amount of carbon in the top meter of Earth’s soil has been estimated to be twice that present as CO2 in the planet’s atmosphere. Consequently, increased decomposition of in the soil—a type of heterotrophic respiration—could make a substantial contribution to global atmospheric CO2 and thus to global warming.
As a result of these relationships, factors that increase heterotrophic respiration could affect global climate. Certain types of land use are reported to affect heterotrophic respiration in soil. For example, deforestation increases CO2 release from soil. In addition, CO2 released into the atmosphere from other sources, such as fossil fuel, can increase global temperatures, which in turn increases the rate of soil heterotrophic respiration, releasing more CO2. The effect of temperature on heterotrophic respiration may be more pronounced in temperate climates than in tropical ones, in which the effect of temperature may already be at or near maximal.
The soil organisms involved in heterotrophic respiration include macro fauna, such as earthworms, insects, and burrowing mammals; micro and meso fauna, such as protozoa and nematodes; and microscopic fauna, such as bacteria and fungi. The major soil heterotrophs are bacteria, in terms of numbers, and fungi, in terms of mass. Cellulose is a major molecule that is transformed into CO2 by the process, and fungi, termites, and bacteria are the main types of organisms that produce enzymes that break down cellulose into simpler compounds.
Bibliography
Bardgett, Richard D. The Biology of Soil: A Community and Ecosystem Approach. New York: Oxford University Press, 2005.
Luo, Yiqui, and Xuhui Zhou. Soil Respiration and the Environment. New York: Elsevier, 2006.
Nissan, Alon. "Global Accelerates Soil Heterotrophic Respiration." Nature Communications, vol. 14, no. 3452, 10 June 2023, https://doi.org/10.1038/s41467-023-38981-w. Accessed 17 Dec. 2024.
Schlesinger, William H. Biogeochemistry: An Analysis of Global Change. New York: Academic Press, 1997.