The Low Molecular Weight Organic Acids in Root Exudates of Leersia hexandra Swartz and Its Role in Mobilization of Insoluble Chromium

Abstract

The root exudates of Leersia hexandra Swartz were collected to investigate their mobilization of chromic oxide (Cr2O3), lead chromate (PbCrO4) and Cr-contaminated soil. It was observed that the root exudates can mobilize Cr2O3, PbCrO4 as well as Cr-contaminated soil. Low molecular weight organic acids in the root exudates L. hexandra were analyzed by high performance liquid chromatography (HPLC). Six organic acids, including oxalic acid, tartaric acid, malic acid, lactic acid, maleic acid and citric acid, were detected in the root exudates, and their concentrations were 18.91±0.23, 130.90±1.44, 1031.34±4.38, 65.54±1.01, 0.96±3.67×10−3 and 201.50±1.13 μg (g root DW)−1, respectively. Chemical reagents of these 6 acids were used to mobilize Cr2O3, PbCrO4 and Cr-contaminated soil. The mobilization of different organic acids to Cr-contamination soil declined in the order of oxalic acid > malic acid > lactic acid > tartaric acid > maleic acid > citric acid. These results suggested that organic acids in the root exudates play an important role in uptaking a large amount of Cr from soil by L. hexandra. Information obtained from this study should develop the understanding of the accumulation mechanism of L. hexandra to Cr in the soil, and provide insights for improving the efficiency of phytoremediation.