Columbia subject headings:
Carbon dioxide--Metabolism--Congresses.
Nitrogen--Fixation--Congresses.
Nitrogen-fixing microorganisms--Congresses.
Plants--Metabolism--Congresses.
Harvard subject headings:
Carbon dioxide--Metabolism--Congresses.
Nitrogen--Fixation--Congresses
Nitrogen-fixing microorganisms--Congresses
Plants--Metabolism--Congresses
Princeton subject headings: