Growth characteristics of ornamental Judas tree (Cercis siliquastrum L.) seedlings under different concentrations of lead and cadmium in irrigation water

Landscape plantations are significantly water demanding in many parts of the world, particularly in dry regions. Adequate water supply is the main limiting factor behind landscape development, maintenance and beauty in such environments. On the other hand, monitoring the growth response of ornamental and landscape plants to irrigation water containing heavy metals can be useful in management and application of municipal wastewaters to these plantations instead of application in edible vegetable crops production, which is common in many urban areas. In the present study, one year old seedlings of Judas tree (Cercis siliquastrum) were irrigated for two years with water containing 0, 15 or 30 mg L–1 of lead (Pb) in absence or presence of cadmium (0 or 5 mg L–1) in a factorial design, and under greenhouse conditions. Heavy metal treatments had no significant effect on leaf SPAD value; however, plants treated with Pb15Cd0 combination had significantly higher SPAD value than Pb30Cd5 combination that showed the lowest leaf SPAD value. Increasing the lead and cadmium levels of irrigation water increased the number of chlorotic and necrotic leaves of plant than control, whereas it reduced the average leaf area and new shoot growth. The control plants or plants treated with lower level of heavy metals showed the highest leaf area and new shoot growth. Leaf photosynthesis rate was significantly reduced in all heavy metal treated plants than control plants, as the lowest amount was in Pb30Cd5 combination treatment. All heavy metal treatments showed higher leaf soluble carbohydrates and proline content than in control plants. Leaf soluble carbohydrates were highest in Pb30Cd0 and Pb30Cd5 treatments, and leaf proline was highest in Pb30Cd5 and Pb15Cd5 treatments. The results indicate that Judas tree is a relatively tolerant species to high concentrations of Pb and Cd in root medium added through the irrigation water, and long term dual application of these heavy metals can have additive harmful effects on plant growth.