Effect of Chromium and Cadmium on Growth Parameters and Biochemical Responses in Soil Treated with Compost and Humic Acid

Abstract

Aims: The effects of chromium (0, 100 and 200 ppm) and cadmium (0, 50 and 100ppm) on shoot dry weight, content of chlorophyll, soluble protein content and  activity of superoxide dismutase (SOD) and catalase (CAT) were investigated. Study Design: The experimental design was completely randomized with 3 replications. Place and Duration of Study: The experiment was car­ried out in the greenhouse of the University of Shahid Chamran in Ahwaz (Iran), between November 2014 and April 2015. Methodology: The experiment was car­ried out in the greenhouse, using soil columns of 20 cm in diameter and 45 cm in depth. The experimental variables were the level of soil contamination with Chromium (0, 100, 200 mg/kg) use K2Cr2O7, Cadmium (0, 25, 50 mg/kg) use Cdcl2 and the type of organic substance (compost and humic acid). Each treatment consisted of: [a] control (without heavy metals (T0) and organic substance); [b] humic acid + T1(25 mg/kg Cd and 100 mg/kg Cr); [c] compost + T1(25 mg/kg Cd and 100 mg/kg Cr); [d] humic acid + T2(50 mg/kg Cd and 200 mg/kg Cr); [e] compost + T2(50 mg/kg Cd and 200 mg/kg Cr). The upper 10 cm of soil was mixed with 40 gr/kg soil compost. The humic acid was a commercial sample from Fluka (product number 35069288) and is used after pretreatment as described by van den Hoop et al. (1999). In short to obtain the soluble fraction of the humic acid, 2.5 g of a Fluka sample were dissolved in 1/1 of water. Seeds of Zea maize (single grass 704) were prepared from Seed Research Centre of Karaj, Iran. The seeds were planted in plastic columns. Each column was filled with 14 kg of soil. Prior to filling, soil was mixed with macronutrients (NPK) and heavy metals. Results: Enhancement of Cr and Cd decrease shoot dry weight and total chlorophyll content of plant in all treatments. Application of organic substance especially humic acid (c) decrease the negative effects of heavy metals. SOD activity increased in treatments, but soluble protein decreased. CAT activity increased in low concentration (T1) of Cr and Cd with significant effect in reaction of the treatment but in high concentration (T2) of this elements CAT activity decreased.  CAT is susceptible to Cr and Cd than SOD, decrees in its activity pointer its. These results show that aggregation of oxygen species due to oxidative stress of heavy metals in plants cause different respond in treatments. Conclusion: In conclusion, our results indicated that the exposure of Zea maize to Cr and Cd decreased shoot dry weight and pigment content. The present study show that in high level of heavy metals antioxidative system in Zea maize was active to survive plant. Decrease in chlorophyll and protein also a signal result for the toxicity of heavy metals. Total Soluble Protein Content decreased in all treatments, indifferently of compound type and Cr and Cd concentration.  Decrease in total soluble protein in most treatments suggests that in this condition (stress of heavy metals) synthesis of protein was destruction. SOD activity increased with the increasing concentration of chromium and cadmium. At higher concentration of Cr and Cd the amount of CAT activity decreased. Increase of SOD pointed to its role in antioxidative system in Zea maize.