Decomposers drive carbon release in soil

Steps:

• Identify the carbon cycle stages: photosynthesis fixes CO2, respiration and combustion release it, decomposition recycles organic matter.
• Focus on soil processes: bacteria and fungi act as decomposers breaking down dead organisms.
• Link to carbon: decomposition releases CO2 back into the atmosphere from organic carbon.
• Eliminate unrelated stages: combustion involves fire, not microbes; photosynthesis and respiration occur in plants/animals without soil microbes.

Why A is correct:

• Decomposition relies on bacteria and fungi as decomposers to break down organic matter, releasing stored carbon as CO2 per the cycle's nutrient recycling role.

Why the others are wrong:

• B: Combustion releases CO2 via burning fuels, independent of soil microbes.
• C: Photosynthesis uses CO2 in plants, driven by sunlight and chlorophyll, not bacteria/fungi.
• D: Respiration releases CO2 from living organisms' metabolism, not requiring soil decomposers.

Final answer: A