Which of the following relations is correct regarding GPP and NPP of an ecosystem?

The correct option is A NPP = GPP - Plant respiration
Gross primary productivity is the rate of production of organic matter during photosynthesis and its considerable amount is utilized by plants during respiration.

Thus Net Primary Productivity is gross primary productivity minus plant respiration.

NPP=GPP-Plant respiration (R)

So the correct option is 'NPP = GPP - Plant respiration'.