Abstract: The effects of shading treatments (full sunlight intensity, 70% sunlight intensity, 40% sunlight intensity) on chlorophyll content, photosynthetic characteristics and growth of Macropanax rosthornii seedlings were examined in a pot-culture experiment. The results showed that shading treatments enhanced the growth performance of the individuals of M. rosthornii with dark green leaves. Both canopy size and the number of compound leaves under shading were significantly greater than those under full sunlight  (P<0.05). The contents of total chlorophyll, chlorophyll a and chlorophyll b in leaves under shading were significantly higher than under full sunlight. The chlorophyll contents increased with the enhanced intensity of shading. On the contrary, the chlorophyll a/b showed a decreasing trend. Under shading, the apparent quantum yield (AQY) and the maximum net photosynthetic rate (P_max) increased, and the light saturation point (LSP) and light compensation point (LCP) distinctly decreased. The efficiency of primary lightenergy conversion (F_v/F_m) and potential activity (F₀/F_m) of PSⅡ were increased by shading, in particular, F_v/F_m and F₀/F_m were significantly  higher under 40% sunlight than under full sunlight (P<0.05). The nonphotochemical quenching coefficients (NPQ) were significantly  lower under shading treatments than under full sunlight (P<0.05), and NPQ further decreased with increasing the shading intensity in which heat dissipation was reduced to increase the efficiency of lightenergy conversion of PSⅡ. Meanwhile, the photochemical quenching coefficient (q_P) was rarely influenced by shading. Thus, as a shaderequiring plant, M. rosthornii had a rather strong ability to utilize low-intensity light and grew well under appropriate shading.

Key words: rainwater interception, extensive green roof, hot and humid region, Guangzhou