Abstract: [Objective] Primary photochemical reactions in leaves of Sabina vulgaris seedlings cultured in iron tailings media under various shading conditions were studied to reveal its light protection mechanism, theoretically explain its natural regeneration process, further understand the light stress on S. vulgaris, and finally to be served for the afforestation management in iron tailings wastelands. [Method] The medium taken from the iron tailings of Qianan was used for potting experiments. The fast chlorophyll fluorescence induction dynamics and the JIP-test analysis method were used to detect 8 fluorescence parameters of the leaves under 5 different treatments including 0%, 25%, 50%, 75% and 90% in shading. [Results] 1) Under full light conditions, Fo increased, Fm decreased, and the quantum yield and the energy distribution ratio (φ_Po, Ψ_o and φ_Eo), specific activity parameters of photosynthetic apparatus in unit area (F_m, ET_o/CS_m, TR_o/CS_m ) and the density of reaction center (RC/CS_m ) were minimum. There were significant or extremely significant differences in the above parameters among the all treatments. The result indicated that the reaction center of photosynthetic system was inactive under full light conditions, but the K and J points of the fast chlorophyll fluorescence induction dynamics curve were higher than those obtained from other shading treatments. The photoinhibition resulted in to a certain degree damages on donor side of PSII (OEC), caused the accumulation of acceptor side of PSII (Q_A^-), and hindered electrons transportation in its electron transport chain. 2) Under full light conditions, φ_Do, F_o and DI_o/CS_m were maximum, and significantly or extremely significantly different from those of shading treatments, suggesting that the photosynthetic apparatus could be protected from damage of excessive solar energy by increasing the heat dissipation through antenna pigments and the dissipation of non radiation energy. 3) With shading ratio increasing, yields or flux ratios (φ_Po, Ψ_o and φ_Eo), phenomenological energy fluxes (ABS/CS_m, ET_o/CS_m and TR_o/CS_m) and the density of reaction centers (RC/CS_m) increased in turn, while absorption flux per CS (ABS/CS_o), quantum yield for energy dissipation (φ_Do) and dissipated energy flux per CS (DI_o/CS_m) decreased. The treatment with 90% shading exhibited the significant light capture characteristic. The average values of F_m and PI_ABS from 50% shading were maximum, suggesting the minimum photoinhibition and maximum photosynthetic capacity of leaves in the shading conditions. There were no significant differences in the other parameters among the diffenrent shading treatments. All the shading treatments did not cause any damages to the acceptor side or the donor side of PSII of S. vulgaris seedlings. [Conclusion] S. vulgaris seedlings were susceptible to light stress without any shading. Therefore, S. cheilophila shrub was selected as nurse plants for the initial stage of natural restoration of S. vulgaris. With growth and development, S. vulgaris gradually achieves its defensive mechanism against photoinhibition through enhancing non radiation energy dissipation, and facilitates the seedlings to well grow under full light conditions without any shading protection. However in in wastelands, some shading treatments were needed in the primary period of afforestation for the higher survival rate.

Key words: shading treatment, iron tailings, Sabina vulgaris seedlings, chlorophyll fluorescence