Which two groups are most commonly responsible for decomposition and nutrient recycling in soils?

• A. Bacteria and fungi
• B. Plants and animals
• C. Algae and protozoa
• D. Insects and worms

Answer: (A)

Decomposition and nutrient recycling in soils are driven mostly by microorganisms, especially bacteria and fungi. They release enzymes that break down dead plant and animal material, turning complex organic compounds into smaller pieces and then into inorganic nutrients that plants can take up. Fungi are particularly adept at decomposing tough plant components like cellulose and lignin because their enzymes can reach and break down these materials in the soil. Bacteria act on a broad range of substrates, often mineralizing organic matter quickly and releasing nutrients such as nitrogen and phosphorus back into the soil.

Other groups contribute in other ways, but they’re not the primary decomposers. Plants and animals produce litter and are producers/consumers rather than the main agents of chemical breakdown. Algae and protozoa participate in nutrient cycling in some environments but have a smaller, less central role in soils compared with microbes. Insects and worms help physically fragment material and mix soil, which aids decomposition, but the key chemical breakdown and nutrient release come from bacteria and fungi.