Effect of light intensity on partitioning of photosynthetic electron transport to photorespiration in four subtropical forest plants

Photosynthetic rate (P-n) and the partitioning of noncyclic photosynthetic electron transport to photorespiration (J(o)) in seedlings of four subtropi cal woody plants growing at three light intensities were studied in the sum mer time by measurements of chlorophyll fluorescence and CO2 exchange. Exce pt Schima superba, an upper canopy tree species, the tree species Castanops is fissa and two understory shrubs Psychotria rubra, Ardisia quinquegona ha d the highest P-n at 36% of sunlight intensity. The total photosynthetic el ectron transport rate (J(F)) and the ratio of J(o)/J(F) Were elevated in le aves under full sunlight. J(o)/J(F) ratio reached 0.5-0.6 and coincided wit h the increasing of oxygenation rate of Rubisco (V-o), the activity of glyc olate oxidase and photorespiration rate at full sunlight, It is suggested t hat an increasing partitioning proportion of photosynthetic electron transp ort to photorespiration might be one of the protective regulation mechanism s in forest plant under strong summer light and high temperature conditions .