Lead Tolerance and Enrichment Characteristics of Three Hydroponically Grown Ornamental Plants

Phytoremediation of lead (Pb) in contaminated soils using hyper-enriched plants is an important task. It is a green and sustainable measure. Studies have revealed that three ornamental plants, Tagetes patula (T. patula), Solanum nigrum (S. nigrum), and Mirabilis jalapa (M. jalapa), have the ability to enrich for Pb; however, studies on difference between them and root morphology and the relationship between tolerance and capacity are lacking. The ability of three lead-enriching plants, T. patula, S. nigrum, and M. jalapa, to cope with Pb stress was assessed in hydroponic experiments using five Pb stress concentrations (0-1000 mg/L). Under different Pb stress conditions, the growth of the shoots and roots of three tested ornamental plants was inhibited to varying degrees. In the three tested ornamental plants, Pb mainly accumulated in the roots, and the highest levels of Pb observed in the shoots of T. patula, S. nigrum, and M. jalapa were 1074.1 mg/kg, 958.7 mg/kg, and 975.3 mg/kg, respectively. All plants reached a critical level of Pb hyperaccumulation. Redundancy analysis showed that changes in the root architecture of the three tested ornamental plants were significantly and positively correlated with tolerance as well as the enrichment and transfer ability of the heavy metal Pb. Therefore, these three ornamental plants have the potential to remediate Pb-contaminated water and soil and can increase the tolerance and enrichment characteristics of Pb by regulating the root biomass and root length of the three test ornamental plants via various agronomic measures. In addition, more research should be conducted to assess their effectiveness as phytoextractants under field conditions.