# Lead Tolerance and Enrichment Characteristics of Three Hydroponically Grown Ormamental Plants
## 3 Results and Discussion
### Effects of Pb Stress on the Enrichment Coefficient and Transfer Factor of Ornamental Plants  
The ability of plants to accumulate heavy metals is generally expressed by the EC value [32]. As the Pb concentration increased, the enrichment coefficients of the shoot and root portions of the tested ornamental plants showed a downward trend (Table 1), and the EC value of the roots of tested ornamental plants was significantly greater than that of the shoots. This finding also demonstrates that the ability of the tested ornamental plants to enrich the heavy metal Pb is greater in the roots than in the shoots. The EC values of the shoots of _T. patula_, _S. nigrum_, and _M. jalapa_ decreased by 1.1 to 3.6, 1.0 to 5.0, and 1.0 to 1.7 with mean values of 2.3, 2.7, and 1.4, respectively. The EC values of the roots decreased by 11.7 to 26.4, 9.8 to 22.0, and 8.1 to 14.7, with mean values of 19.8, 16.4, and 11.4, respectively. The EC values of the roots _T. patula_, _S. nigrum_, and _M. jalapa_ were 8.5, 6.0, and 8.4 times that of the shoots, respectively. Figure 3: Comparisons of root length (**A**), root surface area (**B**), root volume (**C**), and root average diameter (**D**) for tested ornamental plants under different Pb concentrations. _T. patula_, _Tegetes 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. The ability of plants to transfer heavy metals from their roots to shoots is usually expressed by the TF value [32]. With the increase in Pb concentration, the transfer coefficients of the tested ornamental plants _T. patula_, and _S. nigrum_ showed a downward trend (Table 1), and the transfer coefficients of the tested ornamental plants _M. jalapa_ showed a trend that first increased and then decreased. The TF values of _T. patula_, _S. nigrum_, and _M. jalapa_ ranged from 0.09 to 0.15, 0.10 to 0.23, and 0.10 to 0.13, respectively, under different Pb contamination stress treatments with mean values of 0.11, 0.15, and 0.12, respectively. The results show that the order of enrichment ability for Pb was _S. nigrum_ > _M. jalapa_ > _T. patula_. Relationship between Root Morphological Indices and Tolerance, Enrichment, and Transfer Coefficients of Tested Ornamental Plants  
Redundancy analysis (RDA) showed that the root dry weight, root length, root surface area, root volume, and root average diameter of the three tested ornamental plants could explain 92.5%, 88.9%, and 96.5% of the variation in the shoot Pb concentration, tolerance index, enrichment coefficient, and translocation factor of ornamental plants, respectively (Figure 4). Among all the constrained variables, root dry weight had a significant influence on the tolerance index of the three tested ornamental plants (_T. patula_, _S. nigrum_, and _M. jalapa_) and explained 68.4%, 60.7%, and 87.1% of the variance, respectively (Table 2). Among the three tested ornamental plants, only the root diameter of _M.jalapa_ had a significant influence on ornamental plants' enrichment ability for Pb and explained 76.2% of the variance (Table 2). It can be concluded that the biomass and root length of the root systems of the three tested ornamental plants can be adjusted to improve the plants' tolerance and enrichment ability of Pb under different Pb concentration stress conditions. The findings regarding the use of these ornamental plants for phytoremediation or landscaping contaminated areas should be beneficial.