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.

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 organic matter 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 (Bardgett, 2005). 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 (Luo, 2006).

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.

References

1. Bardgett, Richard D. The Biology of Soil: A Community and Ecosystem Approach. New York: Oxford University Press, 2005.

2. Luo, Yiqui, and Xuhui Zhou. Soil Respiration and the Environment. New York: Elsevier, 2006.

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