Effect of Spirulina and Brown Algae and Lead Levels on some Morphophysiological Characteristics of Ornamental Cabbage

Introdaction  Heavy metals are one of the most important environmental contaminants, particularly in soil and water sources. Mining and metal mining activities are major factors in soil contamination and generally surface soil around mines contain high amounts of these metals. Lead (Pb) is one of the heavy metals and important pollutant in arid ecosystem. The use of plants to remove contaminated soil or phytoremediation is an economical method. Today, due to increasing the pollution of soil sources and resultant problems, identification of the resistant plant species against soil pollution is essential. Using lead-contaminated soils requires their decontamination and improvement. There are different methods to remove these pollutions, one of them is the use of phytoremediation to remove pollutants from water and soil or to reduce them. Among the plants that as an ornamental plant can have a covering role in the green space and also perform the work of phytoremediation is the ornamental cabbage plants (Brassica oleracea L.). In this regard, this study was conducted with the aim of investigating the effect of lead heavy metals and the use of brown algae (Polycladia indica) and spirulina (Arthrospira platensis) as biofertilizers on ornamental cabbage plants in the direction of plant treatment. In addition, due to the presence of polysaccharide compounds such as carrageenan and alginate in the cell wall, algae (seaweeds) have a higher ability to absorb many heavy metals. Materials and Methods  The experiment was conducted as factorial based on a completely randomized design in 2020 at the research greenhouse of Zanjan University. The studied factors including lead from lead nitrate source Pb(No3)2 with three concentrations (0, 25 and 50 mg/kg) were applied to the potting soil in four replications in two stages with an interval of two weeks. The second factor was included no algae, brown algae (Polycladia indica) and spirulina (Arthrospira platensis), which occurred in four replications. The measured traits included morphological traits: number of leaves, leaf surface index. Wet and dry root weight, and physiological traits included total chlorophyll content, total leaf antioxidant, peroxidase enzyme, glycine betaine, malondialdehyde, and leaf lead and phosphorus content. Data analysis was performed using SAS software and means were compared by LSD method. Results  The results of the variance analysis showed that different levels of lead and the application of algae had a significant effect on the number of leaves per plant, leaf area index, weight, and drying of roots, total chlorophyll, and antioxidants. Moreover, the interaction effect was significant for leaf area, root fresh and dry weight, antioxidants, and leaf lead content. The simple effect of lead at p≤0.01 significantly affected glycine betaine, malondialdehyde, and leaf phosphorus. When comparing the average mutual effects of lead and algae application, it was found that the treatment with no use of lead and spirulina algae resulted in the highest weight and dry weight of the root, with an average of 11.19 and 3.625 grams, respectively. Additionally, despite the decrease in dry weight of the root due to increased lead concentration, using algae, especially for ornamental cabbage (Brassica oleracea L.), increased the dry weight of the root. The presence of natural plant hormones, organic substances, carbohydrates, fiber and amino acids in algae accelerates rooting, reduces stress caused by heavy metals and absorbs more water due to the presence of o developed root system. Also according to the results of comparing the amount of leaf lead with increasing lead, algae as an auxiliary factor can reduce the amount of uptake in the plant. Leaf phosphorus was also significant due to the simple effect of lead and algae. The highest amount of phosphorus with an average of 0.56% was observed in spirulina and the lowest with 0.48% was observed in control. Conclusion  In general, due to the toxicity of lead metal even in low concentrations, sufficient attention should be paid to the sources of this pollutant entering the environment. In this study, the effective parameters on the uptake of heavy metal lead from the soil by spirulina and brown algae were investigated. The findings of this study indicate that the ornamental cabbage plant is capable of sustaining its growth in the presence of lead and has a high resistance to this heavy metal while simultaneously absorbing it from the soil. Furthermore, the addition of algae as an auxiliary factor can improve the growth of ornamental cabbage under adverse conditions. Therefore, it is recommended that this plant be further examined for its potential to absorb other heavy metals.