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Rationale: Stable isotope approaches are increasingly applied to better understand the cycling of inorganic nitrogen (N i ) forms, key limiting nutrients in terrestrial and aquatic ecosystems. A systematic comparison of the accuracy and precision of the most commonly used methods to analyze δ 15 N in NO 3 - and NH 4 + and interlaboratory comparison tests to evaluate the comparability of isotope results between laboratories are, however, still lacking., Methods: Here, we conducted an interlaboratory comparison involving 10 European laboratories to compare different methods and laboratory performance to measure δ 15 N in NO 3 - and NH 4 + . The approaches tested were (a) microdiffusion (MD), (b) chemical conversion (CM), which transforms N i to either N 2 O (CM-N 2 O) or N 2 (CM-N 2 ), and (c) the denitrifier (DN) methods., Results: The study showed that standards in their single forms were reasonably replicated by the different methods and laboratories, with laboratories applying CM-N 2 O performing superior for both NO 3 - and NH 4 + , followed by DN. Laboratories using MD significantly underestimated the "true" values due to incomplete recovery and also those using CM-N 2 showed issues with isotope fractionation. Most methods and laboratories underestimated the at% 15 N of N i of labeled standards in their single forms, but relative errors were within maximal 6% deviation from the real value and therefore acceptable. The results showed further that MD is strongly biased by nonspecificity. The results of the environmental samples were generally highly variable, with standard deviations (SD) of up to ± 8.4‰ for NO 3 - and ± 32.9‰ for NH 4 + ; SDs within laboratories were found to be considerably lower (on average 3.1‰). The variability could not be connected to any single factor but next to errors due to blank contamination, isotope normalization, and fractionation, and also matrix effects and analytical errors have to be considered., Conclusions: The inconsistency among all methods and laboratories raises concern about reported δ 15 N values particularly from environmental samples., (© 2022 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.)

Spatial variation in the emission rates of nitrous oxide (N 2 O) and methane (CH 4) in soils can be significant due to the diverse biological, chemical, and physical conditions that influence the production and consumption of these gases. Drained organic soils are known to be hotspots for N 2 O emissions, and in wet conditions they can also emit CH 4. We measured N 2 O and CH 4 fluxes during the winter and growing season at 28 locations across a 7-ha area of drained organic agricultural soil in Eastern Finland. Our findings revealed expected high spatial and temporal variations in emission rates. The measured N 2 O emissions varied between −0.003 and 30.4 mg N 2 O m−2 h−1, averaging at 0.94 ± 3.00 mg N 2 O m−2 h−1 and CH 4 emissions varied between −0.27 and 2.90 mg CH 4 m−2 h−1, averaging at 0.10 ± 0.33 mg CH 4 m−2 h−1. Phosphorus concentration was identified as a limiting factor and a critical determinant of spatial variations in N 2 O emissions, whereas CH 4 emissions exhibited a decreasing trend with increasing sulphur and nitrate concentrations. Our study shows that N 2 O and CH 4 fluxes are linked to other elemental cycles, making it critical to identify key nutrient-related processes that govern the spatial and temporal variability in emissions of these gases. [Display omitted] • High spatial variability of N 2 O and CH 4 fluxes in cultivated boreal peat soils • Phosphorus rather than mineral nitrogen was a key predictor for N 2 O emissions • Substantial CH 4 and N 2 O emissions can occur during the winter months • Soil nutrient status is critical to predict GHG emissions from cultivated peat soil [ABSTRACT FROM AUTHOR]