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Do Decomposers Return Nutrients Back Into the Soil?

By Ethan Shaw ; Updated September 21, 2017
Decomposers perform an essential ecological service by breaking down organic matter.
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Not everyone likes to think about decomposition, but messy and dark process ensures the continuation of life on the planet. While we tend to think of a food chain proceeding steadily upward from a lowly plant to a massive predator, decomposers are the ultimate receivers of the energy of such a system -- and they play an essential role in transforming this energy so it can be used in the cycle again.

The Food Web

Decomposers break down dead organisms and other organic matter. Thus they process energy from all levels of the food web, from primary producers like plants and lichens to apex predators. An African lion or grizzly bear may be fearsome and free of predators, but ultimately such beasts are consumed by the bacteria, fungi and other decomposers. Decomposers also feed on waste products such as shed skin cells and fallen leaves. In performing this service, decomposers liberate nutrients from immobilization -- their state when taken up in the tissues of plants and animals -- and mineralize them back into inorganic form, ready for use again by living systems.

Soil Nutrients

Decomposers do indeed return nutrients to the soil -- and to the atmosphere. They extract carbon from their food that, combined with oxygen, creates carbon dioxide. This might transfer to the atmosphere to be utilized again by photosynthesizing plants. Or it may incorporate with groundwater and leaching rainwater to form carbonic acid, a major force of chemical weathering; the substance is greatly responsible for the excavation of limestone and dolomite into caves, caverns, sinkholes and other karst landforms. Also released in decomposition are nutrient compounds of nitrogen and sulfur. Of the former, ammonium, nitrites and nitrates are immensely important for plant growth. Nitrifying bacteria supply such compounds to the soil; denitrifying bacteria transform nitrogen into its gaseous form to be released into the atmosphere.

Decomposers

Bacteria and fungi are some of the major decomposers in soil environments. Various kinds specialize in different parts of the decomposition process. Some fungi and bacteria set to work immediately upon, or even slightly before, the death of an organism, processing easily broken-down substances like sugars and amino acids.

Detritivores

Animal processors of organic materials in the soil are sometimes called detritivores, and are among the participants in the decomposition process. Some of the most prominent of these are the earthworms, members of the so-called soil "macrofauna" -- larger than microfauna like nematodes, smaller than megafauna like ground squirrels. Some species of these worms consume decaying leaf litter and organic particles, excreting nutrient-rich waste matter called castings that substantially elevate levels of humus, potash, phosphorus and nitrogen in the soil.

 

About the Author

 

Ethan Shaw is a writer and naturalist living in Oregon. He has written extensively on outdoor recreation, ecology and earth science for outlets such as Backpacker Magazine, the Bureau of Land Management and Atlas Obscura. Shaw holds a Bachelor of Science in wildlife ecology and a graduate certificate in geographic information systems from the University of Wisconsin.