Recent advances in marine N-cycle studies using ¹⁵N labeling methods

¹⁵N enriched compounds such as ammonium and nitrate, as well as ^15-15N₂ gas are invaluable tools in marine N-cycle research. ¹⁵N stable isotope approaches allow researchers to delve into the often complex world of N-transformations and trace microbially mediated processes such as nitrification, denitrification, anammox and N-fixation. While ¹⁵N stable isotope approaches are well established, experimental approaches which take advantage of them are constantly evolving. Here we summarize recent advances in methodology, including in the direct application of ¹⁵N stable isotopes themselves, improved experimental design and the use of ¹⁵N stable isotopes in single cell studies. Furthermore, we discuss how these advances have led to new insights into marine N-cycling, particularly in the fields of nitrification and N-fixation.