Which of the following statements best describes "carbon fertilization"?

Carbon fertilization refers to the boost in plant growth, especially in C3 plants, when atmospheric CO2 concentration rises. CO2 is the raw material for photosynthesis. At higher concentrations, Rubisco captures more carbon and photorespiration falls, so net photosynthesis and biomass increase. That is option A.

• B is wrong: A rise in temperature due to CO2 is the greenhouse effect, which is a different process.
• C is wrong: Ocean acidification happens when CO2 dissolves in seawater to form carbonic acid, which lowers pH.
• D is wrong: Carbon fertilization is a physiological response of plants. It is not a universal adaptation of all living beings to climate change.

Core concept: the CO2 fertilization effect, a feedback that partly offsets emissions through the terrestrial carbon sink. For Mains, it links to GS3 environment and climate change, especially on whether greening can offset emissions given nutrient and water limits.

Trap: Many pick B or C because they recall CO2 effects on climate or oceans. The word 'fertilization' also sounds like a soil or nutrient idea, so keep the term tied to plant photosynthesis.