Sources of nitrite in a permanent grassland soil

Abstract

SummaryThe objective of this study was to separate the observed nitrite (NO2–) concentration in a permanent grassland soil into process‐specific subpools. A laboratory experiment was carried out where either the nitrate and/or ammonium pool was labelled with 15N at 60 atom % excess. The main N transformations that occurred in this experiment were analysed with a 15N tracing model extended with a NO2– submodel. Techniques that have been used to date have been only able to identify NO2– subpools related to nitrification (NO2–nit) and denitrification (NO2–den). With the analysis presented here, we were able to quantify the size of an additional NO2– pool in the soil related to organic N turnover (NO2–org). All transformations related to NO2– turnover of the three subpools occurred simultaneously. After non‐linear parameter optimization the model predicted that on average NO2–den, NO2–nit and NO2–org pools contributed 57, 33 and 10% to the total soil NO2– concentration. The finding that heterotrophic processes can contribute to the NO2– dynamics in permanent grassland soils might also have important implications for the understanding of gaseous N production that are tightly linked to NO2– turnover. Further work is needed to find out how important the conversion of organic N to NO2– is in other soil‐based ecosystems and to identify the microbial groups responsible for this process.