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Long-term paddy management promotes nitrogen (N) sequestration, but it is unknown to what extent the properties of the parent soil modify the management-induced N sequestration in peptide-bound amino acids (AA-N). We hypothesized that paddy management effects on the storage of AA-N relate to the mineral assembly. Hence, we determined contents and chirality of peptide-bound amino acids in paddy soils developed on contrasting parent material (Vertisols, Andosols, Alisols in Indonesia, Alisols in China, and Gleysol/Fluvisol in Italy). Adjacent non-paddy soils served as references. Selected samples were pre-extracted with dithionite–citrate–bicarbonate (DCB) to better understand the role of reactive oxide phases in AA-N storage, origin, and composition. The results showed that topsoil N and AA-N stocks were significantly larger in paddy-managed Andosols and Chinese Alisols than in their non-paddy counterparts. In other soils, however, paddy management did not cause higher proportions of N and AA-N, possibly because N fixing intercrops masked the paddy management effects on N sequestration processes. Among the different soils developed on contrasting parent material, AA-N stocks were largest in Andosols, followed by Alisols and Fluvisols, and lowest in Vertisols. The N storage in amino acid forms went along with elevated d-contents of bacteria-derived alanine and glutamic acid, as well as with increasing stocks of DCB-extractable Fe, Mn, and Al. Other d-amino acids, likely formed by racemization processes, did not vary systematically between paddy and non-paddy managed soils. Our data suggest that the presence of oxides increase the N sequestration in peptide-bound amino acids after microbial N transformations.

Nitrite (NO2 −) as an important intermediate of the biological nitrogen cycle is particularly reactive in acidic soils and acts as a source of N2O and NOx (NO and NO2). However, abiotic and biotic pathways of NO2 −-driven N2O and NOx production in forest soil and the role of soil organic matter (SOM) in these processes are still unclear. In this study, NO2 − was applied to both unsterile and sterilized soil samples as well as to different SOM fractions from a Norway spruce forest. Biotic and abiotic N2O emission was measured with an infrared absorption analyzer and gas chromatography, while NOx emission was quantified with a chemiluminescence analyzer. Isotopic signatures of N2O (δ15Nbulk, δ18O, and 15N-N2O site preference) were analyzed with an isotope ratio mass spectrometer. After NO2 − addition, a large amount of NOx was emitted immediately, while N2O emission occurred 15–60 min later and was much lower compared to NOx. Sterilization of soil decreased N2O emission significantly, but not NOx emission. The 15N site preference of N2O ranged from 7.98 to 11.58‰ for abiotic and 4.69–7.42‰ for biotic sources. The fulvic acid fraction contributed the most to abiotic N2O emission, while the fastest NO and N2O emission occurred after NO2 −application to the humin fraction, followed by the humic acid fraction. These results are important for the future understanding of NOx and N2O sources, as well as the use of isotopic signatures for source-partitioning N2O emission from soil.