In the context of biogeochemical cycles, how does increasing plant biomass most directly affect atmospheric CO2 levels?

• A. It increases atmospheric CO2 because plants release more CO2 during photosynthesis.
• B. It increases atmospheric CO2 because increased plant biomass reduces carbon storage in soils.
• C. It has no effect on atmospheric CO2 because plants only store carbon in roots and not in aboveground tissues.
• D. It decreases atmospheric CO2 because more carbon is fixed into plant organic matter through photosynthesis.

Answer: (D)

Verified step by step guidance

1. Understand the role of plants in the carbon cycle: Plants absorb carbon dioxide (CO2) from the atmosphere during photosynthesis to produce organic matter.
2. Recognize that photosynthesis is the process where plants convert CO2 and sunlight into glucose and oxygen, effectively removing CO2 from the atmosphere.
3. Consider that increasing plant biomass means more plant material is produced, which corresponds to more carbon being stored in plant tissues (both aboveground and belowground).
4. Know that this increased carbon storage in plant biomass reduces the amount of CO2 in the atmosphere, as carbon is temporarily locked in organic matter rather than existing as atmospheric CO2.
5. Conclude that increasing plant biomass most directly decreases atmospheric CO2 levels because more carbon is fixed into plant organic matter through photosynthesis.