Transboundary air pollution including nitrogen （N） pollutants can be a threat to bryophytes in Japan; especially, those at higher elevations. These pollutants often exhibit higher values of stable isotope ratios of nitrogen （δ15N） than the pollutants emitted from domestic areas; hence, δ15N can be used as a tracer for transboundary pollution. In this study, the exposure of bryophytes to these pollutants at high elevations was evaluated using δ15N and nitrogen content in moss （％Nmoss and δ15Nmoss）. Moss samples （Racomitrium lanuginosum） were collected on 21 mountains in Japan. According to the transboundary airmass type, these mountains were grouped into three regions: Hokkaido, central Honshu, and Yakushima. In Hokkaido, both ％Nmoss and δ15Nmoss showed higher values on the continental side than on the Pacific Ocean side. The δ15Nmoss of the Yakushima region, which is subjected to transboundary pollutants, also showed elevated values. In contrast, the ％Nmoss values in central Honshu decreased with the distance from the continental side; however, the δ15Nmoss did not show any decreasing trends in relation to this distance. These results indicate that R. lanuginosum on the continental side might be more strongly exposed to transboundary N pollutants. However, the indicator values of δ15Nmoss for these pollutants remain disputable. Further analyses are needed to clarify the exposure and influence of transboundary N pollutants on moss at higher elevations in Japan.

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Micromitrium megalosporum Austin Specimen examined: Japan. Kyushu, Miyazaki-ken, Kushima-shi, Nukumi, 125 m elev., 31°29′57″N, 131°11′ 36″E, on soil at paddy field, 19 Oct. 2018, coll. M. Matsumoto in hb. Y. Inoue 6760（HIRO-1149591）． Taiwanobryum speciosum Nog. Specimen examined: Japan. Kyushu, Miyazaki-ken., Nishiusuki-gun, Hinokage-cho, Mt. Togawa, ca. 950 m elev., on limestone, 13 Oct. 2018, coll. M. Matsumoto 4205（NICH-498095）．

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