アカマツ種子の発芽を可能にする有効積算地温とその全国分布

Abstract

The effective cumulative soil temperature in relation to the potential germination of P. densiflora seed was investigated and the results are presented in this study. The laboratory experiment was carried out in the chamber at 5°C, 8°C, 10°C, 15°C, 20°C, 25°C, 30°C and 35°C under both light (3, 000 lx) and dark conditions. The daily germination rate was observed. Initial effective cumulative soil temperature was fixed at 5°C, because the seeds did not germinate at 5°C. From the laboratory experiment at 8°C, 10°C and 15°C, it became obvi ous that, from 75°C•day to 200°C•day (germination period) the P. densiflora seed germinates. Five-day periods of effective cumulative soil temperature, 75°C•day are estimated from the data of the geographical distribution of soil temperature, which is considered to be the beginning of the P. densiflora seed germination in various places. As a consequence, the following facts have been observed (Fig. 4(a)): The first five-day period line of May passes through the southern area of Hokkaido. The first five-day period line of April passes through the Kanto district, Nagano, Gifu, the southern area of Fukui, Tottori Prefectures and Oki Island. That line of March passes through Izu Peninsula, Shizuoka Prefecture, Kui Peninsula, Seto Inland Sea and the central area of Kyushu. The line of February passes through the southern edge of Shikoku and the southern area of Kyushu. Next, the five-day periods of the effective cumulative soil temperature of the ending of the P. densiflora seed germination, that is 200°C•day, are worked out and the results are as follows (Fig. 4(b)): The first five-day period line of June passes through the northeast of Hokkaido. That of May passes through Miyagi, the central area of Yamagata Prefectures and the mountainous area of Jyo-shinetsu. That line of April passes through the south of Honshu, Seto Inland Sea and the central area of Kyushu. The line of March passes through the southern edge of Kui Peninsula, Shikoku and Kyushu. Germination period of P. densiflora seed, that is the period from 75°C•day to 200°C•day, is shorter in northeast Japan compared with that of southwest Japan (Fig. 4(c)). Therefore, there are two deficits in northeast Japan, those are, first the germination time is later and the second the germination period is shorter than in southwest Japan.