Interactive effects of cadmium and carbon nanotubes on the growth and metal accumulation in a halophyte Spartina alterniflora (Poaceae)

Abstract

A study quantifying the interactive effects of cadmium (Cd) and carbon nanotubes (CNTs) on plant growth and Cd accumulation of pot-cultured Spartina alterniflora was conducted. The experiment consisted of two Cd levels (50, 200 mg kg−1) as well as two CNTs levels (800, 2,400 mg kg−1). As expected, CNTs alleviated higher Cd stress (200 mg kg−1) due to restored shoot growth reduction, retrieved water content and resumed plant height. Furthermore, CNTs mitigated the deleterious effects of Cd stress through improving K+ and Ca2+ contents, while reducing Na+/K+ and Na+/Ca2+ ratios, regardless of the level of Cd stress. The proline contents in combined Cd and CNTs treatments were lower than Cd alone, suggesting that CNTs could reduce production of organic solutes under Cd stress. The results also showed higher Cd accumulation in roots than shoots, and both were improved by CNTs, except inhibition in roots under higher Cd stress (200 mg kg−1). It appears that CNTs may not significantly affect negative Cd effects on growth of S. alterniflora, but improve total Cd accumulation under lower Cd stress (50 mg kg−1). However, under higher Cd stress (200 mg kg−1), CNTs restored the reduced plant growth, improved and reduced Cd accumulation in shoots and roots, respectively. Therefore, the effects of CNTs on plant growth and Cd accumulation are different, and levels of Cd stress should be considered when evaluating the combined application of CNTs and S. alterniflora on phytoremediation of Cd pollution.