Nitrogen-15: microbiological alteration of abundance.

The abundance of N(15) relative to N(14) is significantly altered during experiments in vitro in which nitrate and nitrite are microbiologically reduced to nitrogen gas. In all studies to date, N(14)O(3)-and N(14)O(2)-species have been preferentially reduced. This selectivity has a complex dependence on conditions in the medium. The results are not only relevant to natural variations in N(15) relative to N(14) but should be seriously considered during N(15) tracer studies in soils.