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

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 primarily driven by microorganisms, especially bacteria and fungi. These decomposers produce enzymes that break down complex organic matter—like cellulose, proteins, fats, and lignin—into simpler compounds that plants can take up. Fungi are particularly effective at attacking tough materials such as lignin, using their hyphae to access and digest even embedded organic matter, while bacteria rapidly mineralize easier-to-decompose compounds and release inorganic nutrients like ammonium and nitrate. This microbial activity converts organic matter into forms that plants can absorb, sustaining plant growth and soil fertility. Other organisms contribute in supportive ways—plants and animals add and mix organic matter, insects and worms help break things down physically and aerate the soil—but the chemical breakdown of complex polymers is carried out mainly by bacteria and fungi. In soils, those two groups are the main drivers of decomposition and nutrient recycling.