マツ属における落葉季節と落葉型の変遷 : I. 年一回伸長型のマツ類における季節的落葉型式とそれらの獲得

Abstract

マツ類の多様な生活様式を明らかにし, 理解するために, 年l回の新条伸長型を示すマツ類34種の落葉期と落葉した葉の年令を調べ, 次の結果が得られた。1. 中緯度以北の低温域に分布するマツ類の大多数は, 秋に一斉に落葉した。中緯度のマツ類で温暖な地域に分布する種類では, 春秋2回の落葉が認められ, 低緯度地方のマツでは, 年間を通じて落葉する性質が認められた。一部のマツでは生育期間内に落葉する特殊な性質が認められたが, これらの種は分類上, 小亜節に属し, 形質的に古い種であった。2. 秋に一斉に落葉するマツ類は, 原産地の落葉期でなく生育場所, 京都の秋の気温低下に律せられて落葉すると推測された。また, 落葉最盛期は生育場所により異なるものの, 落葉型そのものは生育場所によって変わることはなく, 大まかには, 各種で示した落葉型は原産地の温度条件下で獲得した落葉型を示すものと判断された。年間を通じて落葉するマツでは, 秋の低温に対する葉の感受性が欠如しているものと推測された。3. 落葉した葉は, 古い葉だけが落葉するものでなく, 種のもつ葉の寿命によって落葉の年令構成に多少の差異はあるが, 様々な年令の葉からなっていた。また, 季節的には, 古い葉がやや早く落葉する傾向が認められた。4. マツ属の歴史, 分類形態と様々な落葉型の関係を総合して考慮すると, 生育期間内に落葉するタイプが古く, この落葉型から様々な落葉型が形成されたと考えられた。第四紀以後の気候の寒冷化に伴って, 中, 低緯度地方に分布するマツ類では, 上記のタイプから春秋2回の落葉型の性質を獲得し, さらに冬季に低温となる地域のマツでは, 秋に一斉に落葉する性質を獲得したものと解釈した。

To determine the speciation in the genus Pinus, seasonal falling of needles was measured for 34 pines with single flush type shoot growth. The pines were planted in Kyoto and kept under natural conditions except for some species from subtropical regions. They were cultivated in an unheated greenhouse. The falling of needles from one branch was measured twice a month for two years. Three patterns of needle fall were identified. The needles of the pines brought to Kyoto from northern region (high latitude), which is cooler than Kyoto, fell in autumn. Those of the pines brought from southern region, which has a warm temperate or subtropical region, fell in spring and autumn, and those of the pines brought from the lower latitute region fell throughout the year. Some pines, such as P. pinea, P. bungeana and P. roxburghii, which seem to be old species, had needles falling mainly in summer. Needle fall in autumn seems to be due to a response to the cold in Kyoto at that time, and occurs irrespective of the time the needles fall at their native habitat. Although the time maximum needle fall occurs differs with the habitat, the pattern of needle fall was not changed by the new habitat. That is, the pattern of leaf fall seen at the native habitat seems to have been acquired in response to the temperature conditions at that site. The species with leaf fall occurring throughout the year are considered to lack sensitivity to the cold temperature of autumn. The age of the needles that fell was various, although it also varied with the longevity of the needle. The older needles tended to fall slightly earlier than the younger needles. Judging from the history of the pines, the type of pines with needles falling during the growing season, in the Mesozoic Era, may be one of the oldest, and the other pines probably originated from this type. The pines in the low to intermediate latitude, with needles falling in spring and autumn were derived from this type in response to the cooling climate in the Quaternary period. The falling of needles in autumn was considered to be a character acquired in response to the cold of winter. These leaf fall characteristics are considered to have been kept by these pines to the present.