世代交代に着目した暖温帯性シダの耐寒性

抄録

To understand the adaptation of the life history of ferns to cold climate, freezing resistance of forty ferns collected in Southern Honshu was evaluated as related to the alternation of generations, and the results were compared with those of ferns collected in Hokkaido. The average freezing resistance of the leaf, rhizome, gametophyte and juvenile sporophyte was -9,-6,-14 and -9℃ respectively. The difference in freezing resistance between gametophytes and sporophytic rhizomes was 8℃ in the ferns collected in Southern Honshu and 20℃ in those of Hokkaido. As to the average freezing resistance, the ferns collected in Soukaido showed a higher value than those of Southern Honshu in both generations. The typical difference in the ferns of cool and warm temperate climates throughout the Japanese Archipelago is found between the gametophyte and the sporophyte : however, the difference is not found in subtropical ferns without resistance to freezing temperatures below -9℃. The freezing resistance of the leaf of evergreen ferns of warm temperate and subtropical climates seems to be correlated with leaf injury caused by frost in winter. It was postulated that winter frost constitutes on of the limiting factors of the life cycle of ferns in a temperate climate, and that the sensitive stage is the sporophytic generation, not the gametophytic generation.