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 subtropical woody plants growing at three light intensities were studied in the summer time by measurements of chlorophyll fluorescence and CO(2) exchange. Except Schima superba, an upper canopy tree species, the tree species Castanopsis fissa and two understory shrubs Psychotria rubra, Ardisia quinquegona had the highest P (n) at 36% of sunlight intensity. The total photosynthetic electron transport rate (J(F)) and the ratio of J (O)/J(F) were elevated in leaves under full sunlight.J (O)/J(F) ratio reached 0.5-0.6 and coincided with the increasing of oxygenation rate of Rubisco (V(O)), the activity of glycolate oxidase and photorespiration rate at full sunlight. It is suggested that an increasing partitioning proportion of photosynthetic electron transport to photorespiration might be one of the protective regulation mechanisms in forest plant under strong summer light and high temperature conditions.