Hormesis Effects Induced by Cadmium on Growth and Photosynthetic Performance in a Hyperaccumulator, Lonicera japonica Thunb.

A soil experiment was designed to investigate the hormesis effect of cadmium (Cd) on the growth and the photosynthetic performance in a hyperaccumulator, Lonicera japonica Thunb. by measuring gas exchange, chlorophyll fluorescence parameters, and photosynthetic pigments. After 90 days of exposure to soil containing 25 mg kg(-1) Cd, shoot Cd concentrations reached 168.27 +/- A 5.01 mu g g(-1) dry weight, without showing symptoms of visible damage to the plants. The results also show that Cd at low concentrations (a parts per thousand currency sign10 mg kg(-1)) induced a significant increase in plant biomass, net photosynthetic rate (P (n)), content of chlorophyll (a, b, and a+b) and carotenoids, effective quantum yield I broken vertical bar PSII and photochemical quenching coefficient q (p), but inhibited them at high concentrations (> 25 mg kg(-1)), confirming a hormetic response. The observed growth increases were closely related to the increase in net photosynthesis induced by Cd, though the causes of the P (n) increase are still not understood. The present study suggested that hormetic effects should be taken into consideration in phytoremediation of Cd-contaminated soil and the dose range of Cd inducing hormesis on L. japonica is proposed as 2.5-10 mg kg(-1) in the soil.