Quantifying Biological Processes Producing Nitrous Oxide in Soil Using a Mechanistic Model

Soil nitrous oxide (N2O) is an important source of greenhouse gas contributing to climate change. Many processes produce N2O in soils and the production rate of each process is affected variably by climatic-edaphic factors, making the soil-to-atmosphere N2O flux extremely dynamic. Experimental approaches, including natural and enriched isotopic methods, have been developed to separate and quantify the N2O production from different processes. However, these methods are often costly or difficult to conduct, hampering their widely applications. This study aimed to develop a mechanistic model quantifying the soil N2O production from nitrifier nitrification (NN), nitrifier denitrification (ND), and heterotrophic denitrification (HD), which are considered as the most important biological contributors, and to investigate how climatic-edaphic factors affect individual processes as well as total N2O production rates. The developed model demonstrated its robustness and capability by reliably reproducing N2O productions from the three individual processes of NN, ND, and HD under different moisture contents and oxygen concentrations. The model simulations unraveled how environmental conditions and soil properties controlled the total N2O production rate by regulating individual rates variably. Therefore, the mechanistic model is able to potentially elucidate the large spatiotemporal variances of in-situ soil N2O flux and improve the assessment of soil N2O emission at regional and global scales.