亜熱帯域に分布するイイギリの休眠に関する研究

Liu, Zhen

樹木の季節との同調性, 休眠獲得過程と分布拡大の機構を解明するために, 本研究は, 亜熱帯と温帯にまたがって分布している落葉広葉樹イイギリを用い, 沖縄県産イイギリ種子と頂芽の休眠特性を三重県産のものと比較しながら検討した。その結果, 沖縄県産イイギリの頂芽は, 三重県産と同じく冬休眠に導入された。この冬休眠の導入は日長に影響されず, しかも同じ環境条件下では産地間に差がなかった。また種子と冬芽の休眠は15℃で解除されることは産地間で同じであった。したがって休眠の有無からみた生態型の分化が起こらなかった。ただし, 冬芽の休眠の深さと休眠解除のための効果低温範囲の下限に産地による差が認められたことから地域個体群の分化が起こった。このように, イイギリは凍結の危険性がない亜熱帯北部から冬休眠を獲得し, さらに低い適温に適応した個体群が北上することによって分布を凍結の危険性がある温帯にまで広げたと推察される。これらの結果に基づいて, イイギリの冬休眠を南方系冬休眠と定義し, 北方系冬休眠とタブノキ型休眠と区別した。異なる休眠タイプの樹種では温暖化がもたらす気温の上昇に対する反応が異なると予測した。

The dormancy of terminal buds and seeds of deciduous broad-leaved trees (Idesia polycarpa) from origin of Okinawa prefecture located in the subtropical zone was compared with that from origin of Mie prefecture located in the temperate zone in order to explain the synchronism of trees with seasons and the relations between dormancy induction and distribution . The results showed that terminal buds and seeds in Idesia polycarpa from Okinawa prefecture origin were induced to winter dormancy as the same with those from Mie prefecture origin. Moreover, dormancy induction of buds was not affected by photoperiod and not different between two origins. Furthermore, the dormancy of buds and seeds in Idesia polycarpa from both origins could be released by 15℃. Namely, ecotypes from dormancy did not differentiate in Idesia polycarpa distributing in the subtropical and temperate zone. However, there were some differences in intencity of bud dormancy and the lowest limit of effective chilling temperatures to dormancy release between two origins. So differentiated individual communities from dormancy have emerged in Idesia polycarpa. It was thought that Idesia polycarpa spread its distribution from subtropical zone to temperate zone by getting winter dormancy in the north part of subtropical zone. According to those results, winter dormancy like Idesia polycarpa was defined to southern winter dormancy comparing with northern winter dormancy in northern trees and Machilus thunbergii type's dormancy, which was not induced to winter dormancy. Finally, the effects of global warming were discussed on the growth and development in trees of different types' dormancy.

亜熱帯域に分布するイイギリの休眠に関する研究

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