The Effects of Humic Acid Applications on Heavy Metal Stress in Lettuce

Abstract

In this study was carried out to determine the effects of humic acid in heavy metal stress of lettuce changes in some of the morphological and physiological characteristics. In studies conducted in controlled greenhouse conditions, lettuce plants subjected to four different 4 different humic acid levels humic acid doses (0, 2, 4, 8 L/da) and 4 different heavy metal irrigation levels (Control: 0 ppm; I. mixture: 0.2 ppm Cu + 0.01 ppm Cd + 5 ppm Pb + 2 ppm Zn; II. mixture: : 0.4 ppm Cu + 0.02 ppm Cd + 10 ppm Pb + 4 ppm Zn; III. mixture: 0.8 ppm Cu + 0.04 ppm Cd + 20 ppm Pb + 8 ppm Zn). Four weeks after at heavy metal and humic acid treatment young plants were harvested and the shoot fresh and dry weight, root fresh and dry weight, shoot and root length, and leaf areas, MDA, superoxyde dismutase (SOD) and glutathione reductase (GR) were determined. The most highly toxic effects were determinate III. mixture level (0.8 ppm Cu + 0.04 ppm Cd + 20 ppm Pb + 8 ppm Zn). MDA and antioxidative enzyme activities increased in plants irrigated with water containing a mixture of heavy metal. Humic acid applications had a positive effect on reducing of the limiting effect of heavy metal stress on growth and development.