Effects of sophorolipids augmentation on the plant growth and phytoremediation of heavy metal contaminated soil

Abstract

Heavy metal toxicity to plants and low metal bioavailability in soil decreases the efficiency of phytoremediation. Thus, the present study evaluates the effects of sophorolipids (SL) amendment in heavy metal contaminated soil on the growth of Medicago sativa and Bidens pilosa, and metal uptake efficiency and response towards metal stress in B. pilosa. Results showed that root and shoot lengths of SL augmented plants were found to be higher in comparison to untreated plants. The increase in plant heights was 17% and 11% for M. sativa and B. pilosa, respectively after 60 d of experiment. In another experiment (40 d), presence of Cd in soil (29.2 mg kg−1) negatively affected the phytobiomass of B. pilosa. However, SL augmentation restored the phytobiomass by reducing the toxic effects of Cd on B. pilosa. The dry weights of B. pilosa were 445, 285, and 456 mg plant−1 in control, Cd contaminated soil and Cd and SL treated soil, respectively. SL augmentation decreased the proline concentration in B.pilosa. The observed proline concentration were 18.2 and 40.2 μmoles proline g−1 in SL treated soil and without SL treatment, respectively. Soil urease activity in SL augmented experiment (1.89 μg g−1 h−1) was significantly (p < 0.05) higher than the Cd contaminated (5.7 times) and control (1.5 times) experiments. The Cd accumulation in B. pilosa was also highest in SL augmented soil. The study indicates that SL augmentation is a viable option to induce phytoremediation as it increases Cd accumulation and plant growth, improves the soil microbial activity and reduces metal stress in B. pilosa.