The influence of Pb and Zn on chlorophyll (Chl) fluorescence and plant growth of one-year-old Koelreuteria paniculata and Zelkova schneideriana young plants was investigated. Pb and Zn contents in plant organs were measured. The results showed Pb and Zn stress decreased photochemical quenching and quantum efficiency of PSII, but increased energy dissipation in the tested plants. At the same time, maximum net photosynthetic rate, maximum quantum use efficiency, and organ biomass were reduced.

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... er the same concentration of heavy metals, the damage induced by Zn toxicity was more serious than that of Pb. Pb was less accumulated in leaves, with a mild effect on photosynthesis. Zn was mostly accumulated in leaves and strongly disturbed chloroplast functioning and affected photosynthesis. Pb and Zn had different pathway to influence biomass production, and both tested plants might use different mechanisms of action for heavy metal stress resistance. fluorescence yield of the dark-adapted state; F0' -minimal fluorescence yield of the light-adapted state; Fm -maximal fluorescence yield of the dark-adapted state; Fm' -maximal fluorescence yield of the lightadapted state; Fs -steady-state fluorescence yield; Fv -variable fluorescence; Fv/Fm -maximum quantum use efficiency; PN -maximum net photosynthetic rate; qL -photochemical quenching; TF -translocation factor; YII -quantum efficiency of PSII; YNO -quantum yield of nonregulated energy dissipation; YNPQ -quantum yield of regulated energy dissipation.