Abstract: To investigate the effects of shading and light recovery on the photosynthetic characteristics of peanut seedlings leaves, different shading treatments including no shading, 27% shading, 43% shading, and 77% shading were performed with black sunshade net at the seedling stage of two peanut cultivars Fenghua 1 and Fenghua 2, with related parameters determined. It was shown that with the increase of shading degree, the leaf chlorophyll content, actual PSII photochemical efficiency under irradiance (Ф_PSⅡ), and maximum PSⅡ photochemical efficiency (F_v/F_m) of test cultivars increased, while the Chl a/b ratio and photosynthetic rate(P_n) decreased. On the first day after light recovery, the P_n and stomatal conductance (G_s) decreased while the intercellular CO₂ concentration (C_i) increased with increasing shading degree when measured under high light, but the P_n increased and the G_s and C_i decreased with increasing shading degree when measured under low light. The ratio of P_n measured under low light to that measured under high light increased significantly. With increasing shading degree, the light compensation point, light saturation point, CO₂ compensation point, CO₂ saturation point, and carboxylation efficiency decreased, while the apparent quantum yield increased. After the removal of shading, the P_n, Ф_PSⅡ, and F_v/F_m under natural light decreased immediately, but increased gradually 3-5 days after. 15 days after light recovery, the P_n, Ф_PSⅡ and F_v/F_m in treatment 27% shading recovered to the level of no shading. As for the other treatments, the restored extent differed with shading degree and test variety. In the same treatments, the leaf chlorophyll content, P_n, and Ф_PSⅡ of Fenghua 1 were higher than those of Fenghua 2. The results demonstrated that shading at seedling stage improved the capabilities of test varieties in using low light, but reduced the capabilities in using high light.

Key words: peanut, shading, photosynthetic characteristics, chlorophyll fluorescence, greenhouse vegetable, fertilizer application, yield, evolution rule, Shouguang.