Abstract: Taking the seedlings of mulberry (Morus alba) variety Menggusang as test materials, and by using chlorophyll fluorescence technique, this paper
 studied the effects of irradiance transition on the leaf active photochemical efficiency (Φ_PSⅡ), apparent electron transport rate (ETR), and non-photochemical quenching (NPQ) under different light conditions, and analyzed the changes of three components of NPQ. When the irradiance was transferred from dark or weak light to sunlight, the photosynthetic quantum efficiency of full-light leaves was higher than that of weak-light leaves, the inducible time responses of full-light leaves’ Φ_PSⅡand ETR were faster to reach steady state as compared to those of week-light leaves’, and the induction of full-light leaves’ NPQ had a trend of rapid increase in the first two minutes and slow decrease subsequently. The state transitional quenching component (q_T) of full-light leaves under high light condition made up 18% of the total non-photochemical quenching (NPQ), whereas the q_T of weak-light leaves only amounted to 7% of NPQ, which meant that the mulberry leaves under full-light condition could adapt to the changes of light intensity by means of higher efficiency of photosynthetic quantum and greater contribution to the adjustment of light energy between photosystem Ⅰ (PSⅠ) and photosystem Ⅱ (PSⅡ), compared to the leaves under weak-light condition.

Key words: mulberry (Morus alba L.), photochemical induction, non-photochemical quenching, state transition, Castanopsis carlesii secondary forest, clear-cutting, logging residue, decomposition rate, chemical composition.