Phytotoxicity of Cu2+ and Cd2+ to the roots of four different wheat cultivars as related to charge properties and chemical forms of the metals on whole plant roots

Abstract The relationship between the chemical forms of Cu2+ and Cd2+ adsorbed on the roots of different wheat cultivars and their phytotoxic effects on the plants were investigated. The wheat varieties Dunmaiwang (DMW), Tekang 6 (TK6), Zhongmai895 (ZM895), and Chaojixiaomai (AK68) were used. The zeta potentials of wheat roots, measured by the streaming potential method, were used to characterize root charge properties. Results indicated that the changes in zeta potential at pH 4.01–6.61 were 14.7, 15.53, 13.01, and 12.06 mV for ZM895, AK68, DMW, and TK6, respectively. The negative charge and functional groups on ZM895 and AK68 roots were greater than on DMW and TK6 roots, which led to more exchangeable and complexed Cu2+ and Cd2+ on ZM895 and AK68 roots and increased Cu2+ and Cd2+ toxicity compared to DMW and TK6. Coexisting cations, such as Ca2+, Mg2+, K+, and NH4+, alleviated Cu2+ and Cd2+ toxicity to wheat roots through competition for adsorption sites on the roots, which decreased exchangeable and complexed Cu2+ and Cd2+ on wheat roots. The Ca2+ and Mg2+ were most effective in alleviating heavy metal toxicity and they decreased exchangeable Cu2+ on AK68 roots by 39.14% and 47.82%, and exchangeable Cd2+ by 8.51% and 28.23%, respectively.