Abstract:

Malus hupehensis seedling were cultured in a 1/2 strength Hoagland solution with pH3, pH4 and pH6 to study effects of acidity in rhizosphere on their photosythesis, the net photosynthesis (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i) and chlorophyll fluorescence parameters in the leaves in 8 days after tredtment. The results showed that the P_n and G_s reduced, the C_i raised; the efficiency of light energy capture by open photosystemⅡ (PSⅡ) reaction centers (F' _v/F' _m), maximum photochemistry efficiency of PSⅡ(F_v/F_m), actual quantum yield of PSⅡ(Φ_PSⅡ), photochemical quenching of PSⅡ(q_P) reduced; the fluorescence intensity F_k at 300 μs increased, and the quantum yield for electron transport (φ_Eo), the performance index on absorption basis (PI_ABS) and the density of active reaction center (RC/CS) all decreased significantly. Furthermore, the range of variation of these parameters increased with reducing pH the solution of rhizosphere. These results displayed that rhizosphere acidification damaged the oxidation and reduction sides of the reaction centers of PSⅡ of the leaves in M. hupehensis, and further decreased the activity of PSⅡand P_n.

Key words: Malus hupehensis, rhizosphere acidity, photosynthetic rate, photosystemⅡ, chlorophyll fluorescence