Selection of the Most Effective Cultivar of Genus Zinnia Flowers for Phytoremediation of Oil-contaminated Soil

Low-cost and environmentally friendly removing processes for contaminated soil by oil, such as phytoremediation, are being evaluated in recent years. We aimed to select the most effective cultivar among 6 cultivars in 4 species of genus Zinnia (Z. elegans cultivars ‘Uproar’ and ‘Zahara’, Z. angustifoliacultivar ‘Starbright’, Z. haageana cultivars ‘Sombrero’ and ‘Oldfashion’ and Z. hybrida cultivar ‘Profusion’) that can be grown under Japanese environmental conditions for the phytoremediation of oil-contaminated soils. In addition, both total petroleum hydrocarbon (TPH) concentration of the soil and the soil dehydrogenase activity (DHA) were assessed over the growth period. The above-ground and under-ground dry matter weights of 6 cultivars in non-contaminated plot were significantly higher than those in contaminated plot. However, plant heights of 6 cultivars at 180 days after sowing in contaminated plot were as high as those in non-contaminated plot. Growth of ‘Starbright’ was the latest in all cultivars, and ‘Uproar’ and ‘Sombrero’ at 180 days after sowing in contaminated plot was curled up the above ground. These results were judged that ‘Starbright’, ‘Uproar’ and ‘Sombrero’ were not suited for growing in contaminated soil. The TPH concentration in soil significantly decreased by about 70% from an initial concentration of 13,191mg diesel kg-1 soil after 180 days in the contaminated soil for all 6 cultivars. In particular, the TPH concentrations of ‘Sombrero’, ‘Profusion’, and ‘Starbright’ decreased to 74%, 72%, and 72%, respectively. Soil DHA of 6 cultivars in contaminated plot at 180 days after sowing were significantly higher than that of irrigated plots, especially those of ‘Starbright’ and ‘Profusion’ were much higher compared to the other 4 cultivars. These results clarified that ‘Profusion’ and ‘Starbright’ are suited for high remediation in contaminated soil.