Gao et al.: Effects of lead stress on chlorophyll and photosynthetic fluorescence characteristics of Vallisneria natans -4171 -APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 17(2):4171-4181. Abstract. In order to reveal the effects of lead stress on the chlorophyll content and fluorescence characteristics of Vallisneria natans, six Pb concentration levels were applied to a culture in clean river sand and water. The results showed that Pb could promote the synthesis of chlorophyll at a low

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... ion (Pb ≤ 10 mg·L -1 ) in one day. V. natans had certain tolerance to the stress of low Pb concentration. With the prolongation of stress time and increasing Pb concentration, the leaves of V. natans gradually lost their green color. Chlorophyll a decreased more than chlorophyll b. It had the least effect on carotenoids. Fv/Fm, Fv/Fo, qP, Y(II) and ETR decreased significantly (Pb > 10mg·L -1 ) in seven days. However, qN, Y(NO) and Y(NPQ) showed an upward trend. The efficiency of the leaves using light energy decreased noticeably, and the electron transport of PSII was blocked severely. It can be speculated that V. natans may be used in the phytoremediation of waters contaminated by a low concentration of lead. APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 17 (2) :4171-4181.