What is one major role of bacteria in soils?

• A. Rapid nutrient cycling
• B. Increasing soil water retention
• C. Directly fixing atmospheric carbon for plants
• D. Providing soil color

Answer: (A)

Bacteria in soils are central to turning organic matter into forms that plants can use, speeding up nutrient availability. They decompose complex organic compounds and mineralize nutrients such as nitrogen and phosphorus, releasing ammonium, nitrate, and phosphate that plants can uptake quickly. This rapid nutrient cycling keeps soil fertility high and supports plant growth in rangeland systems.

Increasing soil water retention depends largely on soil texture, structure, and organic matter content rather than microbial action as the primary driver, so this isn’t the main role of bacteria. Directly fixing atmospheric carbon for plants isn’t how carbon gets into plant biomass—plants do most carbon fixation through photosynthesis, with some bacteria fixing carbon only for their own use. Soil color is mainly controlled by minerals and organic matter; microbes influence soil chemistry only indirectly.