## 3 Results
The highest plant accumulation of cadmium was recorded after three weeks at the lower level of supplementation (Table 4); these conditions were found to favor the greatest efficiency of metal accumulation (100%) (Figure 4). In turn, the lowest cadmium accumulation was observed after three weeks, but at the higher nutrient level. At both nutrient levels, longer exposure to cadmium resulted in lower plant cadmium accumulation (Table 4). The least efficient cadmium uptake (67%) was observed after six weeks at the lower nutrient level; after this time, cadmium uptake increased to 81% at the higher nutrient level (Figure 4). The addition of cadmium salt to water had a significant effect on the fresh weight and the number of rosettes of the frosbit. After cadmium supplementation, but only at a higher nutrient level, a slight increase in fresh weight rosette number was found after six weeks (Tables 5 and 6). In the other cases, cadmium had a negative effect on plant growth and development (Tables 5 and 6), as confirmed by a tolerance index lower than one (Figure 5). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**Conditions**} & \multicolumn{4}{c}{**Linear Correlation**} \\ \hline \multirow{2}{*}{**PNK Level**} & \multirow{2}{*}{**Term**} & \multirow{2}{*}{**Equation**} & **Regression** & \multirow{2}{*}{**Probability (\(p\))**} & **Value of** \\  & & & **Coefficient I** & & & **Correlation** \\ \hline \multirow{2}{*}{low} & I & C\({}_{\text{P}}\) = 18.58 + 6233.1 \(\times\) C\({}_{\text{w}}\) & r = 0.5536 & \(p\) = 0.0619 & - \\  & II & C\({}_{\text{P}}\) = 6.28 + 678.1 \(\times\) C\({}_{\text{w}}\) & r = 0.9013 & \(p\) = 6 \(\times\) 10\({}^{-5}\) & very high \\ \hline \multirow{2}{*}{high} & I & C\({}_{\text{P}}\) = \(-\)18.22 + 1977.7 \(\times\) C\({}_{\text{w}}\) & r = 0.6876 & \(p\) = 0.0135 & high \\  & II & C\({}_{\text{P}}\) = 22.13 + 279.9 \(\times\) C\({}_{\text{w}}\) & r = 0.3168 & \(p\) = 0.3158 & - \\ \hline \multicolumn{2}{c}{C\({}_{\text{w}}\) = Cd concentration in water; C\({}_{\text{P}}\) = Cd content in _Hydrocharis moss-rane_.} \\ \end{tabular}
\end{table} 
Table 3: The linear correlation between the cadmium concentration in water (ug Cd\(\cdot\)dm\({}^{-3}\)) and the cadmium content in _Hydrocharis moss-rane_ (ug Cd\(\cdot\)g\({}^{-1}\) d.w.) in the three tested growing seasons. Figure 3: The indicator of cadmium contamination in _Hydrocharis moss-rane_ in the three tested growing seasons. Similar letter indicates no significant difference (\(p\leq 0.05\)). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**Conditions**} & \multicolumn{4}{c}{**Heavy Metal (HM)**} \\ \hline \multirow{2}{*}{**PNK Level**} & \multirow{2}{*}{**Term**} & \multicolumn{2}{c}{**0**} & \multicolumn{2}{c}{**Cd**} \\ \cline{3-5}  & & **Average** & **Standard Error** & **Average** & **Standard Error** \\ \hline \multirow{2}{*}{low} & I & 15.0 b  & 0.6 & 13.3 cd  & 0.7 \\  & II & 14.3 bc  & 0.4 & 10.0 e  & 1.0 \\ \hline \multirow{2}{*}{high} & I & 20.6 a  & 0.8 & 15.4 b  & 1.3 \\  & II & 12.1 d  & 1.3 & 13.8 bed  & 0.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The number of _Hydrocharis morsus-ranae_ rosette in the three tested growing seasons. Figure 4: The cadmium uptake efficiency index by _Hydrocharis morsus-ranae_ in the three tested growing seasons. Similar letter indicates no significant difference (\(p\leq 0.05\)). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**Conditions**} & \multicolumn{4}{c}{**Heavy Metal (HM)**} \\ \hline \multirow{2}{*}{**PNK Level**} & \multirow{2}{*}{**Term**} & \multicolumn{2}{c}{**0**} & \multicolumn{2}{c}{**Cd**} \\ \cline{3-5}  & & **Average** & **Standard Error** & **Average** & **Standard Error** \\ \hline \multirow{2}{*}{low} & I & 19.9 b  & 0.38 & 18.1 cd  & 0.34 \\  & II & 18.9 bc  & 0.43 & 14.3 e  & 0.37 \\ \hline \hline \multirow{2}{*}{high} & I & 25.8 a  & 0.35 & 19.1 bc  & 0.43 \\  & II & 17.3 d  & 0.46 & 18.2 cd  & 0.38 \\ \hline \hline \end{tabular}
\end{table}