Effects of Cd concentrations on growth, photosynthetic indices and bioconcentration of two Pennisetum during different growth stages

The growth, photosynthetic indices of Pennisetum americanum(ML) and P. americanum×P. purpureum(ZL) under different cadmium(0,5,25,50,75,100 mg·kg-1)were investigated by pot experiment and make a comparison between the two cadmium tolerance and the difference on the absorption and transport of cadmium. Results showed that: 1) the plant height decreased after increasing Cd concentration, fresh weight and dry weight decreased while leaf width changed no significant with the Cd concentration increased at the same growth stage; the indicators above increased gradually with the extension of the growth period at the same Cd concentration, however leaf width and fresh weight of ZL showed bigger; 2) At the same growth stage, Chla and Chlb content in ML were more than ZL. When Cd concentration at 5 mg·kg-1, it showed little effects on the net photosynthetic rate, transpiration rate, intercellular carbon dioxide concentration, but with the Cd concentration increased each treatment became significantly decreased compared with the control(P<0.05), which indicated that high concentrations of Cd treatment had significant effect on the photosynthesis of Pennisetum especially ZL. 3) Growth performance of American pennisetum was better than hybrid pennisetum, while the bioconcentration factor was less, indicating that the former had better tolerance to Cd, and the latter was more suitable for the remediation of cadmium contaminated soil. 4) the root system is the main bioconcentration site and Cd in root part transfered little to the overground part, in three growth stages,the content of Cd was the highest in seedling stage, which showed the seedling stage was when the plant was the most susceptible to Cd stress. ZL had a better effect than ML on the remediation of cadmium contaminated soil. If the soil under low Cd concentrations(<1.0 mg·kg-1), pennisetum still can be used as edible forage.