Growth responses to the rapid change of light condition were examined for saplings of Quercus serrata growing under canopy. The saplings were transplanted in pots and carried to four experimental plots, that were open plot, large-gap and small-gap plots, and under-canopy plot as control. In saplings transferred in April, after the development of early-season shoots late-season shoots emerged in open plot and large-gap plot. The area of the late-season foliage attained to 2 and 1.3 times as much as that of the early-season foliage in open plot and large-gap plot, respectively. Values of pmax, light saturated photosynthetic rate of foliage, increased with an increase in relative PPFD of experimental plots, except for open plot. However the differences due to light condition in ∅, photochemical efficiency of photosynthesis, were not as pronounced as those in pmax. The late-season foliage had higher values of pmax, 1.4 to 2.2 times as high as the early-season foliage. In saplings transferred in July, late-season shoots did not emerged in any plots and the increase of pmax in early-season foliage with increasing relative PPFD was not so large. In saplings transferred in July the shedding of early-season foliage occurred in open plot immediately after transferring, followed by regeneration of new shoots. Throughout the whole saplings, the weight of individual increased in the dependency on light interception by foliage. The emergence of lateseason foliage and regeneration foliage which had high photosynthetic ability took an important role in improving productivity of the saplings.

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Net photosynthesis and transpiration of3-year old seedlings of apple (Malus pumila Mill. var. dulcissima Koidz.) and black locust (Robinia pseudoacacia L.) were measured as diurnal courses and seasonal fluctuation from May to October in 1994. The soil moisture of apple and black locust was set on three levels by controlling the irrigated amount of water. Both species showed reductions of net photosynthesis during most measurements in low water conditions. Black locust reduced its transpiration at noon during most measurements in low water conditions. Distinct seasonal fluctuations of integrated daily CO₂ uptake and H₂O release were measured in both species, and yield a seasonal fluctuation of daily water use efficiency also. Integrated daily CO₂ uptake and H₂O release of both species decreased in low water conditions, but yielded a low daily water use efficiency in apple and a high value in black locust as the degree of reduction of integrated daily CO₂ uptake and H₂O release were different. The productivity of apple was higher than that of black locust with a very high water consumption during the same water stress conditions. Therefore we can conclude that black locust is more drought-tolerant than apple.

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[in Japanese]

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