Effects of cadmium (Cd) on seedling growth traits and photosynthesis parameters in cotton (Gossypium hirsutum L.).

Abstract

Cadmium (Cd) is a widespread toxic heavy metal that usually causes deleterious effects in living organisms. In this study, the effects of Cd on seedling growth traits and photosyntheses parameters in cotton were investigated. The seedlings at three-leaf stage cultured in four nutrient solutions containing different Cd concentrations (0, 25, 50, and 100 μM) were subjected to assay the growth traits and the photosyntheses parameters. The growth traits analyzed included plant height, leaf area, biomasses of leaf, root, and stem, whereas the photosynthetic parameters measured included chlorophyll (Chl) content, gas exchange, and chlorophyll fluorescence. The results indicated that after 3 and 7 d treatments of Cd, the growth of cotton seedlings was significantly inhibited, showing that the plant height, biomass, and leaf area were all decreased. The Cd treatments also affected the photosyntheses parameters of the cotton seedlings. Under treatments of 50 and 100 μM concentrations of Cd, the seedlings exhibited significant decreases on Chl a and Chl b, photosynthetic rate (Pn), stomotal conductance (Gs), transpiration rate (E), maximal photochemical efficiency (Fv/Fm), quantum yield of electron transport (ΦPSII), photochemical quenching (qP), and electronic transport rate (ETR) (P≤0.05). However, the Chl a/b and Ci were increased after the Cd treatments. The dramatic variations of chlorophyll fluorescence values under Cd treatments in comparison with the control (CK) suggested that the photosystem II (PS II) activity in cotton seedlings was much more sensitive to Cd toxicity. Taken together, our results confirm that Cd significantly inhibits the growth traits as well as the photosynthetic parameters in cotton seedlings. The non-stomata limitation, Chl reduction, and PSII system damage act as main limiting factors for affecting photosynthesis and cotton seedling growth under the Cd treatment.