Effects of Temperature on Growth and Photosynthesis in Impatiens (Impatiens walleriana Hook.f.)

Impatiens are one of the most popular bedding plants used for landscaping during autumn, winter and spring season in northern part of Taiwan. High temperature during summer season impairs the growth of impatiens. The five series of impatiens（Impatiens walleriana Hook.f） including 45 commercial cultivars were planted at the urban and suburban areas in the northern part of Taiwan and planted at different growing seasons of Dec, 2001 and Mar, 2002 to evaluate landscaping performance among cultivars. The results showed that the factors of planting areas and planting seasons affected the growth and performance of impatiens that showed temperature was the major factor. Under optimum temperature circumstance, most impatiens cultivars grew well and performed well until 150 DAT. But heat stress occurred, the results showed difference of performance among 45 impatiens cultivars and plant quality only maintained to 90 DAT.Four cultivars of impatiens (Impatiens walleriana Hook.f.) were studied in a phytotron at different day/night temperature of 15/13, 20/15, 25/20, 30/25 and 35/30°C to investigate the effects of different day/night temperatures on growth and photosynthesis. High temperature 35/30°C impaired the growth and decreased the height, number of leaves, branches, shoot dry/fresh weight and flower size. The net photosynthesis decreased sharply at 35/30°C. As temperature increased from 15/13 to 35/30°C, the dry weight of roots decreased and almost stopped at 35/30°C. High temperature affected the root growth more than shoot growth.The effects of high root temperatures on growth and photosynthesis in two cultivars of impatiens were studied in a growth chamber that the day/night temperature was set at 25/20℃. Five root temperatures were set at 25, 27.5, 30, 32.5 and 35℃ using hydroponic unit equitted with heating system. Results showed that high root temperature would ≧32.5℃ impair plants growth and photosynthesis and root temperature ≧30℃ would inhibit root growth. In conclusion, the root growth of impatiens was sensitive to high root temperature that any way to reduce root temperature would increase landscaping performance.