Basic Ecophyisiological Research On Effects Of Simulated Acid Rain On Field-grown Vicia Faba L.

The effects of simulated acid rain on gas exchange, chlorophyll fluorescence and chlorophyll content in leaves of Vicia faba L. (Lincan II) were investigated. The results showed that photosynthesis was inhibited by acid rain of pH3.0 and pH2.0, but not be affected markedly by acid rain of pH4.5. After three-time treatments with acid rain of pH3.0 the net photosynthetic rate (Pn) , stomatal conductance (Gs) and intercellular CO₂ concentration (Ci) were significantly decreased and stomatal limitation (Ls) was increased. No significantly changes were observed in chlorophyll fluorescence. All these parameters could be recovered to the level of control after the treatment ended. After treatment with acid rain of pH2.0, the net photosynthetic rate, stomatal conductance, maximum photochemical efficiency of PSII (Fv/Fm) and actual photochemical efficiency of PSII (Opsn) were rapidly reduced, but intercellular CO₂ concentration was initially decreased, then increased. Chlorophyll content and chlorophyll a/b value were significantly decreased. All above data suggested that after treatment with acid rain of pH3.0 the decreased Pn was resulted from the restriction of CO₂ entrance by stomata. And after beginning treatment with acid rain of pH2.0, the declined Pn was due to the stomatal limitation, but after three times treatment the non-stomatal factors predominated in the decline of Pn. The growth and biomass of Vicia faba L. were also affected by acid rain. The root length was significantly inhibited by acid rain of pH3.0, the drought weight of bean root was markedly decreased after treating with acid rain of pH3.0 and pH2.0, the root shoot ratio was significantly inhibited by acid rain of all pH value. Furthermore, there were different effects of simulated acid rain of different pH value on the water potential and water content of bean leaves.