Question

which of the following would increase the productivity of a plant when added to an ecosystem? soil oxygen nitrogen

Explanation:

Plants require nitrogen (a key macronutrient) for synthesizing proteins, DNA, and chlorophyll, which directly boosts growth and productivity. Soil is a medium for plant growth but not a limiting additive in most established ecosystems, and oxygen is abundant in the atmosphere for plant respiration, not a limiting factor for productivity.

Answer:

nitrogen