Effects of Cadmium Stress on Leaf Chlorophyll Fluorescence and Photosynthesis of Elsholtzia argyi--A Cadmium Accumulating Plant.

A hydroponic experiment was conducted to investigate the effects of cadmium (Cd) on chlorophyll fluorescence and photosynthetic parameters on a Cd accumulating plant of Elsholtzia argyi. Four weeks-seedlings of E. argyi were treated with 0 (CK) 5, 10, 15, 20, 25, 30, 40, 50 and 100 μmol L(-1) Cd for 21 days. Fv/Fo, Fv/Fm, qP, ΦPSП, ETR and Fv'/Fm' were significantly increased under low Cd (5-15 μmol L(-1) for Fv/Fo, Fv/Fm and qP, 5-10 μmol L(-1) for ΦPSП, ETR and Fv'/Fm') stress, and these parameters were similar to control under Cd≤50 μmol L(-1). All above parameters were significantly decreased at 100 μmol L(-1) Cd. Compared with control, Pn was significantly (P<0.05) increased under 5-30 μmol L(-1) Cd. However, 50 and 100 μmol L(-1) Cd significantly (P < 0.05) reduced it. Gs and Tr were substantially decreased at 50-100 and 40-100 μmol L(-1) Cd, respectively. Ci was significantly increased at 50 and 100 μmol L(-1) Cd. High Cd-induced decrease of Pn is not only connected to stomatal limitation but also to the inhibition of Fv/Fo, Fv/Fm, ΦPSП, qP, ETR and increase of NPQ. Maintain chlorophyll fluorescence and photosynthesis parameters under its Cd tolerance threshold were one of tolerance mechanisms in E. argyi.