Decomposer

A decomposer is an organism that breaks down dead or decaying organic matter, returning inorganic nutrients to the environment. In most ecosystems, decomposers are primarily microorganisms such as fungi and bacteria, with other microbes and certain invertebrates contributing to the process. They typically achieve this through saprotrophic nutrition, secreting extracellular enzymes that digest complex polymers—such as cellulose, lignin, proteins, and fats—into simpler compounds that they can absorb.

Decomposition is a central part of nutrient cycling and soil fertility. By mineralizing organic material, decomposers convert carbon, nitrogen, phosphorus, and other elements into forms that primary producers can reuse. This process sustains plant growth and supports broader ecosystem productivity, influencing soil structure and ecosystem resilience.

Mechanisms and factors: Decomposers rely on extracellular enzymes to break down substrates outside their bodies. Decomposition rates are influenced by substrate quality, temperature, moisture, oxygen availability, and pH. Fungi are especially important for breaking down tough plant polymers like lignin, while bacteria often dominate the initial breakdown of simpler organic molecules and rapid turnover.

Organisms and relationships: The principal decomposers are fungi (including many basidiomycetes and ascomycetes) and bacteria. Archaea and some protists also contribute in specific environments. Detritivores such as earthworms and woodlice physically fragment litter and speed up decomposition, but they are distinct from decomposers, which digest material externally.

Applications and impacts: Decomposer activity underpins composting, wastewater treatment, and bioremediation efforts. Decomposition also releases carbon dioxide to the atmosphere, and in anaerobic environments may produce methane, influencing greenhouse gas dynamics.