Concentrations of dissolved 29N2 and 30N2 in core incubations after 48 h in R4 cores and 24 h in W27 cores. R4-experiment 1 was amended with 15NH4+ and standard NO3-. R4-experiment 2 was amended with 15NO3- and standard NH4+. W27-amended core was amended with 15NO3-. The omission of a bar indicates that the production of that gas was negligible.