Photosynthetic Response to Temperature in Heptacodium miconioides Seedlings

Abstract:

Heptacodium miconioides Rehd. (Caprifoliaceae) i s a monotypic and endangered species endemic to China. Mature leaves of 3-year-o ld seedlings of this species were used to determine the photosynthetic rate, tra nspiration rate and stomatal resistance in response to light intensity and tempe rature. Optimum temperature for net photosynthetic rate was 26-30℃. There was a power equation between dark respiration rate and temperature at 19-40℃, and a linear relationship between transpiration rate (Tr) and temperature．Highest saturated light intensity，apparent quantum yield，and Pmax appeared in the seedlings at 29℃，but they were the contrary at 39℃．Light compensation point and Tr increased obviously and the photoinhibition was enhanced at 39％．High temperature decreased carboxylation eficiency and increased CO₂ compensation point，which led to a significant decrease of photosyn thetic capacity．It is suggested that mild shading culture of H．miconioides seedlings is beneficial to the reduction of leaf temperature and photoinhibition in the summer．