15N2 as a tracer of biological N2 fixation: A 75-year retrospective

Abstract

15N2 has played a crucial role in fundamental studies of biological N2 fixation. However, due to operational constraints, it has more often served as a qualitative rather than a quantitative tracer of biologically-fixed N (BFN). Therefore indirect methods based either on 15N-enrichment or 15N-natural abundance have assumed a dominant role in quantifying N cycle processes involving BFN. However, it is only through the direct 15N2 approach that biological N2 fixation can be traced through the various components of the soil-plant system. Technological advances in the automated control of the chamber environment have made the 15N2 technique more attractive to long-term studies. Thus the need to ..