The effect of low molecular weight organic acids on the growth, antioxidant capacity, and lead enrichment of duckweed (Landoltia punctata) under Pb stress

Lead (Pb) is one of the most harmful, toxic pollutants to the ecological environment and humans. Duckweed , a fast-growing aquatic plant , is excellent for remediation of Pb pollution. Low molecular weight organic acids (LMWOAs) are more efficient, environmentally friendly and biodegradable than inorganic chelating agents, but the effects of LMWOAs on the tolerance and Pb enrichment of duckweed are still unclear and which LMWOAs has the best enhancing effect remains to be further studied. In this study, we screened out the optimal Pb-enriched duckweed ( Landoltia punctata 0021) from 60 duckweed samples. We then investigated the effects of LMWOAs, including citric acid (CA), malic acid (MA), tartaric acid (TA), and oxalic acid (OA), on the Pb enrichment abilities of this duckweed. The results showed that the addition of CA significantly increased the biomass, the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), reduced malondialdehyde (MDA) content and mitigated oxidative damage of duckweed compared to CK. The enhancement effects of the four LMWOAs on duckweed Pb enrichment were CA>MA> TA>OA. The effect of different concentrations of CA was further investigated, and it suggested that the Pb enrichment and BCF of duckweed were highest at 500 μM. These results indicate that CA and 500 μM are considered the best LMWOAs and CA treatment concentration for Pb-contaminated water remediation with duckweed. The study may provide a new idea for the remediation of Pb-polluted water by duckweed combined with LMWOAs. • The enhancing effects of LMWOAs on the Pb tolerance of duckweed decreased in the order CA>MA>TA>OA. • CA is considered the best candidate for Pb-contaminated water remediation with duckweed. • 500 μM CA is considered the best concentration for Pb-contaminated water remediation with duckweed.