Laurence Y. Yeung, Joshua A. Haslun, Nathaniel E. Ostrom, Tao Sun, Edward D. Young, Maartje A. H. J. van Kessel, Sebastian Lücker, and Mike S. M. Jetten

Abstract

We describe an approach for determining biological N₂ production in soils based on the proportions of naturally occurring ¹⁵N¹⁵N in N₂. Laboratory incubation experiments reveal that biological N₂ production, whether by denitrification or anaerobic ammonia oxidation, yields proportions of ¹⁵N¹⁵N in N₂ that are within 1‰ of that predicted for a random distribution of ¹⁵N and ¹⁴N atoms. This relatively invariant isotopic signature contrasts with that of the atmosphere, which has ¹⁵N¹⁵N proportions in excess of the random distribution by 19.1‰. Depth profiles of gases in agricultural soils from the Kellogg Biological Station Long-Term Ecological Research site show biological N₂ accumulation that accounts for up to 1.6% of the soil N₂. One-dimensional reaction-diffusion modeling of these soil profiles suggests that subsurface N₂ pulses leading to surface emission rates as low as 0.3 mmol N₂ m^-2 d^-1 can be detected with current analytical precision, decoupled from N₂O production.

10.1021/acs.est.9b00812