Physiological and microstructural responses of two Rhododendron cultivars to high temperature and low light

Rhododendrons (Rhododendron) are ornamental plants that exhibit poor thermotolerance. To provide a theoretical basis for the production and application of Rhododendron in summer, effects of high temperature and low light stress on the growth, physiological characteristics (including photosynthesis), and leaf structure of Rhododendron were explored. Two Rhododendron cultivars, Rh. 'Fen Zhenzhu' and Rh. 'Zhuangyuan Hong', were selected. Rhododendron plants were subjected to stress in 6-day intervals in an artificial climate box with 37.5, 75, 112.5, and 150 mu mol m(-2) s(-1) photosynthetic photon flux at 38 degrees C. The leaf anatomical parameters and physiological indexes, including gas exchange parameters, relative water content, relative conductivity, chlorophyll and osmotic substance contents, malondialdehyde and hydrogen peroxide levels, and enzyme activity, of Rhododendron under high temperature and different low light levels were measured. The results showed that the combined stressors of high temperature and low light caused damage to leaves, such as loss of water, cell membrane damage, decreased net photosynthetic rate, and changes in leaf structure. Additionally, with the decreased light intensity caused more damage, and different damage mechanisms were found in different cultivars and treatments.