Answer: The correct answer is -
Producers.
Plants take up nitrogen from soil in the form of ammonium ions (which is a fixed form of nitrogen through nitrogen fixing bacteria present in the soil), nitrate or nitrite ions.
They take up the nitrogen by absorption through roots. It is then incorporated into amino acids, which are further used in protien synthesis.
As plants are producers (that is they can synthesise their own food using carbon dioxide and water in the presence of sunlight), therefore, second option is the right answer.