Root Characteristics and Metal Uptake of Maize (Zea mays L.) under Extreme Soil Contamination

Root characteristics and metal uptake in the maize hybrid Naudi were studied in a pot trial, using soil artificially highly polluted with Zn, Cu, Co, Cd, and Pb. The addition of these metals as sulfates decreased the soil pH and increased electrical conductivity. As a result of increased bioavailability in the soil pore water, significantly higher concentrations of metals, particularly Pb, Cu, and Co, were found in the shoot tissues of maize at the 3-4 leaf stage. While the lowest increase was in Cd (0.89 mg kg(-1) vs. 0.33 mg kg(-1) for controls), Zn reached a critical threshold of 75 mg kg(-1) vs. 2.76 mg kg(-1). Fresh and dry weights of shoots and roots, as well as root length, were markedly reduced, whereas root diameter, tip density, and the branching index increased considerably. A significant adaptation strategy by maize in the polluted soil was an increased fraction of coarse root length and a decreased fraction of finer roots. We conclude that maize is very sensitive to multiple metal pollution, suggesting its potential use as a test plant to evaluate contaminated soils. As length was the most affected root characteristic, measurement of this parameter could be a way of screening genotypes for tolerance to metal contamination and possibly salinity. There also is future scope for investigating whether K fertilization might mitigate metal phytotoxicity, in view of the negative correlations between the shoot K concentration and concentrations of the supplied metals.

Automated summary

In a pot trial using soil contaminated with Zn, Cu, Co, Cd, and Pb, root characteristics and metal uptake in the maize hybrid Naudi were studied. The pollution led to higher concentrations of metals in the shoot tissues, reduced fresh and dry weights of shoots and roots, and changes in root diameter, tip density, and branching index. Maize showed sensitivity to multiple metal pollution, suggesting its potential use as a test plant for contaminated soils.