Which statement best describes how soil microbes contribute to nutrient cycling?

• A. Blocking all nutrient flows.
• B. Producing sterile soil.
• C. Removing all nutrients from soil.
• D. Decomposing organic matter and releasing nutrients.

Answer: (D)

Soil microbes drive nutrient cycling by decomposing organic matter and releasing nutrients. Bacteria and fungi break down dead plant and animal material, turning complex organic compounds into simpler inorganic forms that plants can uptake, such as ammonium, nitrate, phosphate, and sulfate. This mineralization makes essential nutrients available again in the soil. Some microbes also transform nutrients through processes like nitrification and phosphate solubilization, helping keep nutrients in forms that plants can use. By breaking down material, they support soil fertility and plant growth. While immobilization can temporarily trap nutrients during decomposition, the overall effect is to release nutrients rather than block them or strip the soil of nutrients. The other options describe actions that don’t happen with microbial activity in soil.