Seasonal changes of photosynthetic activity of leaves in
Zelkowa serrata (a deciduous tree) and some evergreen trees, were investigated and meaning of concerning dry matter production was discussed.
1. The photosynthetic activity of
Zelkowa increased rapidly up to its maximum value of 5-6mg. CO
2/50cm
2./hr. later in April and the value persisted for about 2 1/2 months; afterwards the activity decreased slowly until the defoliation in November. The activity maintained itself above a half value of the maximum for about 4 1/2 months of which mean monthly temperatures were above 17°. The photosynthetic activity changed fairly parallel, but only apparently, to the chlorophyll content.
2. In late spring and summer, the courses of change in the photosynthetic activities in evergreen trees,
Shiia Sieboldi, Pittosporum Tobira and
Cinnamomum Camphora, were more or less similar as that of
Zelkowa. In late autumn the activity fell to a low level, and it continued throughout the winter, and only in
Pittosporum the activity recovered before the leaf fall in next late spring.
3. The younger stage of leaf is characterized with a higher respiration and compensation point, and with a lower chlorophyll content and photosynthetic activity. These were clearly shown in the leaves of a Lammas shoot which have generally higher activity than those of ordinary shoot.
4. The weight of the leaves of
Shiia and
Pittosporum is ca. 180g./m
2., while that of
Zelkowa is ca. 90g./m
2., hence, to get back these invested capitals the former species must earn about double amount of dry matter. In southern districts this may be easily realized in warmer winter, and which makes the evergreen tree more advantageous in competition with the deciduous tree in natural distribution.
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