Anthropogenic disturbance of the nitrogen (N) cycle has more than doubled the amount of reactive N circulating in the biosphere. This session seeks to improve our understanding on how various microbial processes contribute to N cycling in terrestrial and aquatic ecosystems, how global changes impact ecosystem N biogeochemistry and what feedbacks from N cycling will be most important in influencing the climate. The presentations will cover all aspects of ecosystem N cycling, especially methodological advances in measuring and modelling of microbial N-transformation processes such as denitrification, nitrification, co-denitrification, nitrifier-denitrification, nitrate ammonification (DNRA) or anerobic ammonia oxidation (ANAMMOX), as well as their contributions to exchange of gaseous N species (N2, N2O emissions) under field-like conditions. The session will also highlight innovative isotopic, molecular and modelling methods on N cycling communities and processes at various scales, interactions with other element cycles (e.g., carbon, phosphorus), terrestrial-aquatic linkages, and feedbacks to global change.