Abstract
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.
