EFFECT OF HUMIC ACID APPLICATION ON CADMIUM ACCUMULATION BY LETTUCE LEAVES

Abstract

Humic acid (HA) is a plant growth stimulator compound that may also reduce cadmium (Cd) concentration in plant tissues. The aim of the present study was to investigate the effect of adding humic acid (HA) to the growth medium on Cd concentration in lettuce leaves. In a soilless experiment, seedlings of lettuce (Lactuca sativa L.) were exposed to three levels of Cd [0, 2 and 4 mg L⁻¹ in the form of cadmium chloride (CdCl₂)] and three levels of HA (0, 100 and 1000 mg L⁻¹). Application of HA increased significantly the shoot fresh weight of lettuce while it had no effect on the photosynthetic rate and concentrations of chlorophyll, proline, and phosphorus (P) in lettuce leaves. In contrast, increasing Cd concentration was associated with decreases in the photosynthetic rate, shoot fresh weight, and leaf chlorophyll concentration. A significant reduction in leaf Cd concentration was found by addition of HA to the growth media. It seems that application of HA could be successful for improving plant growth and reducing accumulation of Cd in edible parts of lettuce.

Keywords:

• photosynthetic rate
• proline
• vegetables
• heavy metal

ACKNOWLEDGMENTS

The authors are grateful to Zhejiang University. This project was supported by the UNESCO Foundation.