Rapid light-response curves of PSⅡ chlorophyll fluorescence parameters in the leaves of Salix babylonica, Salix ‘J172’ and Salix leucopithecia to Cd2+ stress

The effects of Cd 2+ on rapid lightresponse curves of photochemical and nonphotochemical chloropyll fluorescence quenching parameters were investigated under different cadmium treatments based on the determination of chlorophyll fluorescence parameters. Dark fluorescence yield (F0) and maximal fluorescence yield (Fm) of Salix babylonica, S. ‘J172’ and S. leucopithecia were investigated under different concentrations of Cd2+ solutions (0,50,100,200,400 mg/L) by a MINIIMAGINGPAM chlorophyll fluorometer. The results showed that F0 and Fm significantly increased compared with control, and the two parameters reached the maximum under the stress of 200 mg/L Cd 2+ for 2 weeks. The rapid lightresponse curves of chlorophyll fluorescence parameters of the three willow (Salix spp.) trees were also measured at various light intensities. The parameters of maximal PSⅡ quantum yield (Fv/Fm), effective PSⅡ quantum yield (PSⅡ) and coefficient of photochemical quenching (qP) decreased according to the increase of light intensity. The PSⅡ and qP declined significantly under Cd 2+ stress at the same light intensity compared with control. The parameters of quantum yield of regulated energy dissipation (YNPQ), coefficient of nonphotochemical quenching (qN), and electron transport rate (ETR) increased with elevation of light intensity. The YNPQ, qN, and ETR increased sharply under Cd 2+ stress at same light intensity. No significant change was found for quantum yield of nonregulated energy dissipation(YNO) of the three willow trees with the aggrandizement of light intensity. The results indicate that S. leucopithecia shows torelence to Cd 2+ by reversible inactivation of PSⅡ reaction center.