PROBLEM TO BE SOLVED: To connect a nitrous oxide reducing bacterium to a plant through a symbiotic relationship, to provide a symbiont stably absorbing the nitrous oxide in the atmosphere and to provide a method for reducing the nitrous oxide using the symbiont. SOLUTION: The symbiont of the bacterium with the plant so as to exhibit reducing actions on the nitrous oxide even under aerobic conditions where oxygen is present is provided. As one example, the symbiont by a Pseudomonas sp. CM1 strain (accession number NITE AP-240) and Zoysia japonica is provided. COPYRIGHT: (C)2008,JPO&INPIT