Effect of Humic Acid on N, P and Stress Indicators of Lettuce Polluted by Cadmium

Information is still scarce about exposure to toxic heavy metal in Iran. The attempt was made to study about the prevention effect of humic acid (HA) on Cd absorption by lettuce (Lactusa sativa) A factorial CRD experiment was conducted in hydroponic system with 7 replications. Treatments were: control (no additions)، HA (0، 100 and 1000 mgL-1)، and Cd (0، 2 and 4 mgL-1). Cd uptake along with enzyme activities، superoxide dismutase (SOD)، peroxidase (POD)، proline and biomass of lettuce were measured. A significant increase in SOD and POD activity and proline content were observed with increasing cadmium. Cd content increased together with biomass and organic acid decreased in plants received cadmium. The POD activity increased up to 8 and 53% and SOD to 66 and 106 and proline content to 39 and 119% with 2 and 4 mgL-1 of cadmium respectively. HA did not affect P and proline content. HA decreased the toxic effects of Cd through optimizing SOD، POD activity and fresh weight. Therefore، adding HA to lettuce plants stressed by Cd can alleviate the toxic effect of cadmium.