Effects of Cadmium Stress on Photosynthetic Physiological Characteristics of Two Rorippa Species

The photosynthetic physiological characteristics of Rorippa amphilia and Rorippa sylvestris were studied by pot experiment under Cd stress, and 7 Cd treatments were 0, 1, 5, 10, 50, 100, 200（mg·kg-1）respectively. The results showed that, (1) The Chla, chlb, and Ch(la+b) changed little when the Cd concentration in the soil was less than 100 mg·kg-1. There was no significant difference among the treatments. When Cd concentration was more than or equal to 100 mg·kg-1, all indexes decreased significantly, Chla/b increased gradually with the increase of Cd stressful concentration; (2) Net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) first increased and then decreased with the increase of Cd stressful concentration, while intercellular carbon dioxide concentration (Ci) increased significantly; (3) The photochemical quenching coefficient (qP) and electron transfer rate (ETR) decreased gradually with the increase of Cd stressful concentration, while the non-photochemical quenching coefficient (NPQ) increased with the increase of Cd stress concentration. It indicated that the photosynthetic mechanism of leaves was damaged; the maximum photochemical quantum yield (Fv/Fm) and potential activity (Fv/Fo) of PSII decreased gradually with the increase of Cd stress concentration. When Cd concentration was more than 50 mg·kg-1, the decrease was very obvious, showing photoinhibition. The concentration of Cd below 50 mg·kg-1 had little effect on photosynthesis. These results provide a theoretical application by using these two species of Rorippa to ecological restore the Cd contaminated farmland and abandoned mines.