# Lead Tolerance and Enrichment Characteristics of Three Hydroponically Grown Ormamental Plants
## 3 Results and Discussion
### Effects of Pb Stress on the Pb Content of Ornamental Plants  
Lead stress had a significant effect on the Pb content in ornamental plants (\(p<0.05\)). With the increase in the Pb concentration, the Pb content in the aerial and underground portions of the tested ornamental plants increased significantly (Table 1). Compared with the CK, the Pb content of the shoots and roots of ornamental plants showed a clearly  
Figure 1: Responses of fresh and dry weights of the shoots and roots of ornamental plants with increasing Pb concentrations under hydroponic conditions (**A–D**). _T. patula, Tagetes patula. S. nigrum, Solanum nigrum_ and _M. jalapa, Mirabilis jalapa_. CK, the Pb concentration in hydroponic solutions was set to 0 mg/L. T1, the Pb concentration in hydroponic solutions was set to 100 mg/L. T2, the Pb concentration in hydroponic solutions was set to 200 mg/L. T3, the Pb concentration in hydroponic solutions was set to 500 mg/L, and T4, the Pb concentration in hydroponic solutions was set to 1000 mg/L. The different lowercase letters indicate significant differences under the tested Pb concentrations for the same ornamental plants at the \(p<0.05\) level.  
Figure 2: Tolerance index of the shoots and roots of tested ornamental plants under different Pb concentrations (**A,B**). _T. patula, Tagetes patula. S. nigrum, Solanum nigrum_ and _M. jalapa, Mirabilis jalapa_. CK, the Pb concentration in hydroponic solutions was set to 0 mg/L. T1, the Pb concentration in hydroponic solutions was set to 100 mg/L. T2, the Pb concentration in hydroponic solutions was set to 500 mg/L, and T4, the Pb concentration in hydroponic solutions was set to 1000 mg/L. The different lowercase letters indicate significant differences under Pb concentrations for the same ornamental plants at the \(p<0.05\) level. Other symbols are the same as in Figure 1.  
increasing trend, especially in the underground portion of the Pb, with a significant increase in amplitude. In the specific analysis, the Pb content of the shoots of the ornamental _T. patula_, _S. nigrum_, and _M. jalapa_ plants increased by 8.3- to 24.9-, 14.7- to 27.8-, and 3.9- to 25.4-fold with a mean fold increase in values of 16.6, 21.8, and 13.7, respectively. The Pb content of ornamental plants in roots increased by 43.1- to 189.5-, 41.7- to 168.6-, and 31.3- to 172.9-fold with mean fold increase in values of 114.9, 99.2, and 90.9, respectively. The experimental results show that the content in the roots of ornamental plants was significantly greater than that in the shoots, and the Pb content in the shoots of the tested ornamental plants increased multi-fold compared to the control, which is consistent with the study on _Tegetes minuta_ and _Bidens pilosa_[28]. The result was reasonable and similar to the results of previous studies (4-20 times higher); however, the fold increase in the root compared with the control far exceeded the shoot parts. A possible reason for this is that most heavy metal ions are stored in root cells and are bound to the cell wall in plants [29]. The Pb content reached 1074.1 mg/kg for _T. patula_ only under the 1000 mg/L treatment.