Variations in root morphology among 18 herbaceous species and their relationship with cadmium accumulation.

This study aims to investigate whether root system morphology is involved in the interspecific variations in Cd accumulation in herbaceous plants. Biomasses, root morphology, and Cd accumulation of 18 herbaceous species were determined under 0, 2, and 10 mg kg Cd conditions. Significant variations were found in biomass production, root system morphology, and Cd accumulation among the 18 species. Cd concentrations in the shoot had negative correlations with the biomass of roots and shoots in the 2 mg kg Cd treatment. Total amounts of Cd in plants showed positive correlations with the biomass of roots and shoots, total root lengths, root surface areas, root volumes, and proportions of the fine roots (diameter <0.2 mm). Percentages of Cd in shoots were positively related to specific root lengths, root surface areas, and plant biomasses but negatively correlated with proportions of roots in the 0.6-0.8-mm diameter class. High-biomass species (rapeseed, Indian mustard, and four-o'clock) have high Cd uptake capacity due to their large root system. Longer and thinner roots might contribute to higher capacity for transferring Cd from roots to shoots, while coarse roots (i.e., diameter of 0.6-0.8 mm) could retain more Cd in the tissues and, consequently, reduce Cd transfer from roots to shoots.