Root morphological responses of five soybean [Glycine max (L.) Merr] cultivars to cadmium stress at young seedlings

To examine the differences in root morphological responses of soybean cultivars with different cadmium (Cd) tolerance and accumulation to Cd stress, the biomass, Cd concentration, and root morphological features of five soybean cultivars were determined under 0, 9, 23, 45, and 90 μM Cd stress via hydroponic experiments. Significantly genotypic differences in Cd tolerance and Cd concentration were observed between five soybean cultivars at four Cd levels. For Cd tolerance, HX3 showed a strong Cd tolerance with tolerance indexes of shoot biomass at 92.49, 76.44, 60.21, and 46.45 % after 18 days at four Cd levels, and others had similar weak tolerance at young seedling. For Cd accumulation, Cd concentration in roots showed far higher than that in shoots. The different accumulation features in roots and shoots among five cultivars were found at four Cd levels. Comparing with the control, the total root length (RL), root surface area (SA), and root volume (RV) of all cultivars were decreased significantly at four Cd levels. Tolerant cultivar HX3 had the largest root system and sensitive cultivar BX10 had the smallest root system at young seedling stage. Correlation analysis indicated that RL, SA, and RV were positively correlated with root biomass and shoot biomass under 9 and 23 μM Cd treatments, but root average diameter (RD) was negatively correlated with shoot biomass and root biomass only under 9 μM Cd treatments, while RL and SA were negatively correlated with root Cd concentration under 23 and 45 μM Cd treatments. The results suggested that root morphological traits were closely related to Cd tolerance at young seedlings under Cd treatments.