A microbial-explicit model with comprehensive nitrogen processes to quantify gaseous nitrogen production from agricultural soils.

Agricultural soils are a major source of anthropogenic N 2 O, but their N 2 O emission estimates are highly uncertain, mainly due to the complexity of nitrogen (N) processes. Most soil N models include only primary N processes such as nitrification and denitrification, which limits their ability to realistically simulate N transformations in soils and accurately estimate N 2 O emissions from soils. This study introduces a Microbial-Explicit Model incorporating Comprehensive Nitrogen processes (MEMCN) to evaluate and quantify the influences of various N processes on the production of N 2 O as well as NO and N 2 , including nitrification, denitrification, anaerobic ammonium oxidation (ANAMMOX), dissimilatory nitrate reduction to ammonium (DNRA), mineralization, and microbial assimilation (i.e., growth) and death. The MEMCN was evaluated in laboratory experiments using agricultural soils with different levels of N additions under anaerobic and aerobic conditions, and reproduced well the dynamics of NH 4 +, NO 3 −, NO 2 −, NO, N 2 O, and N 2. After nitrification and denitrification, ANAMMOX and assimilation were found to be most important in controlling N transformations in agricultural soils. ANAMMOX directly increased N 2 emissions by 139% at the beginning of the simulations (i.e., 48 h) under anaerobic conditions, while microbial assimilation indirectly reduced NO, N 2 O, and N 2 emissions by 88%, 54%, and 58%, respectively, at the end of the simulations (i.e., 336 h) under aerobic conditions. Correspondingly, the biomass of ANAMMOX bacteria increased significantly at the beginning of the simulations under anaerobic conditions, while the biomass of nitrite oxidizing bacteria increased substantially under aerobic conditions. In contrast, DNRA, mineralization and microbial death had minor effect on soil N transformations, and the biomass of DNRA bacteria and heterotrophs did not change significantly during the simulations. Our study shows that it is necessary to include ANAMMOX and microbial assimilation in soil N models, while explicit simulation of microbial biomass dynamics may only be necessary if microbial biomass pools change significantly. • Develope a Microbial-Explicit Model incorporating Comprehensive N processes. • Quantify contributions of individual N processes to gaseous N production. • ANAMMOX increased N 2 produciton under aerobic and anaerobic condtions. • Assimilation reduced NO, N 2 O, and N 2 emissions under aerobic condtions. • Micoribal biomass should be explicitly expressed as they change substantially. [ABSTRACT FROM AUTHOR]