Effects of High Temperature on Photosynthesis, Membrane Lipid Peroxidation and Osmotic Adjustment in Four Rhododendron Species

In order to make clear the response mechanism of Rhododendron species to high temperature, two– year–old seedlings of R. fortunei, R. ovatum, R. simsii and R. mariesii were heat–stressed at 42°C/30°C (day/night) for 24 h. Four Rhododendron species under heat stress showed significant differences in heat injury indices (HII), and R. fortunei was more sensitive to high temperature than the other three species. The lipid peroxidation of R. fortunei seedling was most serious indicated by malondialdehyde (MDA), which could be related to the significant decrease of superoxide dismutase (SOD) activity in R. fortunei seedlings. In the other three heat–resistant species, the content of soluble proteins and SOD activity increased under heat stress. The accumulation of proline and soluble sugars was found in greater heat– resistant species, which could alleviate osmotic stress of rhododendron seedlings under high temperature. Net photosynthesis (PN) rates for four species were inhibited at different levels due to heat stress, but reduction proportion of PN for R. fortunei was highest due to mainly nonstomatal factors.