Effect of winter climate change on soil nitrogen (N) biogeochemical processes was synthesized based on Japanese case studies.

Ammonium-N was dominant for soil inorganic N fertility under cold environments.

Net ammonification enhanced by increased soil freezing–thawing cycles.

Further needs of comparative research with the analyses of microbial composition and functions, overwinter impacts, and the long-term legacy effects using global site network (i.e., ILTER) were addressed.