1995 Volume 21 Issue 4 Pages 199-211
Net photosynthesis and transpiration of3-year old seedlings of Japanese cypress (Chamaecyparis obtusa Endl.) and Japanese red pine (Pinus densiflora Sieb. et Zucc.) were measured as diurnal courses and seasonal fluctuation from May to November in1994. Three levels of soil moisture were achieved by controlling the irrigated amount of water. Net photosynthesis of both species peaked in the morning, transpiration reached its peak later than net photosynthesis. Net photosynthesis and transpiration decreased in lower water conditions as well as stomatal conductance. However, no distinct differences in water use efficiency was observed among all three treatments. Integrated daily CO2uptake peaked in July, for Japanese cypress; and in August, for Japanese red pine. Integrated daily H2O release had similar patterns to integrated daily CO2uptake in most treatments except pF2.7of Japanese red pine, whereas it peaked in October. Daily water use efficiency was higher in early summer and late autumn than in mid summer, for Japanese cypress; but was relatively steady, for Japanese red pine. Integrated daily CO2uptake and H2O release of both species decreased in lower water conditions. However, there was no significant difference among all three treatments in daily water use efficiency. Net photosynthesis of Japanese red pine was higher than that of Japanese cypress under the same water stress conditions. Japanese red pine is more drought-tolerant than Japanese cypress.
