つる植物の生育に日照条件が及ぼす影響

Abstract

日照条件がつる植物の生長に及ぼす影響を明らかにするために, 東西南北の4方位に向けた壁面を設定し, これにナツヅタ (Parthenocissus tricuspidata Planch.) を沿わせて育成し, それらの伸長量を毎月一度測定するとともに, 日射量, 壁面温度, 葉面温度などの日変化を夏に測定し, 次の結果を得た。1. 夏の晴れた日の日射量は, 南面では正午付近で最大値を持つ一山型の日変化を示した。東面は午前に, 西面は午後に大きな値を示し, 北面では朝に一時的に大きな値を示した。日積算量は南, 東, 西, 北の順であった (図-2)。東と西の差は, 地形条件によるものであった。2. 夏の晴れた午前中の壁面温度は9時頃東面で最高となり, 44℃程度となった。正午頃には南, 東, 西面での壁面温度が同程度の値を示し, 38℃程度になり, 北面が最低で, 34℃程度となっていた。午後に曇天になってからは, 4方位間で壁面温度に差はなかった (図-3)。3. 壁面温度と同じ日に測定した葉面温度は, 壁面温度の変化にほぼ同調するが, やや低くなっていた。午前中に東面で高く, 一時的に35℃程度となり, 正午頃には南, 東, 西面では, ほぼ同じ値を示し, 33℃程度であり, 北面では, 30℃ほどであった (図-4)。4. 4月に定植したつる植物の4方位面での生長の差は, 秋 (9月) 以降に明確となり統計的に有意なものとなった。北, 西面で生長がよく, 南, 東面で悪い結果となっていた。これらの結果から, 南, 東面での日射量の過多がつる植物の生長に対して阻害要因として働いていたと推測された。

In order to clarify the effects of sunlight conditions on the growth of a climbing plant, the shoots of Parthenocissus tricuspidata Planch. which were growing on walls faced to the four directions were measured once in a month. In summer, the diurnal change of : the solar radiation, the wall surface temperature and the leaf surface temperature were measured. The results were as follows ; 1. On a sunny day of summer, diurnal change of solar radiation which was measured on the wall faced to the south showed a mount shape with the maximum value at noon. On the wall faced to the east the value was high in the morning, on the wall faced to the west the value was high in the afternoon, and on the wall faced to the north the value was high in the early morning for a short time. The accumulation of solar radiation was highest on the wall faced to the south, followed by the east, west and north wall in that order (Fig. 2). The difference between the east and west wall was caused by surrounding terrain elevation. 2. On a sunny morning of summer, wall surface temperature was highest at 9 a. m. on the wall faced to the east (about 44℃). At noon, there were not big differences among the south, east and west walls (about 38℃), but on the north wall the surface temperature was lowest (about 34℃). As it became cloudy in the afternoon, there were no differences among the four directions (Fig. 3). 3. The leaf surface temperature which was measured on the same day showed similar results as the wall surface temperature, but it was a little lower. In the morning, it was highest on the east wall (about 35℃). At noon, there were small differences among the south, east and west walls (about 33℃), but on the north wall the leaf surface temperature was lowest (about 30℃) (Fig. 4). 4. Among the four directions, the differences of growth of the shoots of Parthenocissus tricuspidata Planch. which were planted in April became clear and statistically significant from September. The growth of the shoots was greater on the walls faced to the north and west directions than to the south and east directions. From these results we concluded that excessive solar radiation on the walls faced to the south and east directions affect the growth of Parthenocissus tricuspidata Planch. as an obstructive factor.