Salinity and Heavy Metal Tolerance, and Phytoextraction Potential of Ranunculus sceleratus Plants from a Sandy Coastal Beach

Abstract

The aim of the present study was to evaluate tolerance to salinity and different heavy metals as well as the phytoextraction potential of Ranunculus sceleratus plants from a brackish coastal sandy beach habitat. Four separate experiments were performed with R. sceleratus plants in controlled conditions: (1) the effect of NaCl gradient on growth and ion accumulation, (2) the effect of different Na⁺ and K⁺ salts on growth and ion accumulation, (3) heavy metal tolerance and metal accumulation potential, (4) the effect of different forms of Pb salts (nitrate and acetate) on plant growth and Pb accumulation. A negative effect of NaCl on plant biomass was evident at 0.5 g L^-1 Na⁺ and growth was inhibited by 44% at 10 g L^-1 Na⁺, and this was associated with changes in biomass allocation. The maximum Na⁺ accumulation (90.8 g kg^-1) was found in the stems of plants treated with 10 g kg^-1 Na⁺. The type of anion determined the salinity tolerance of R. sceleratus plants, as Na⁺ and K⁺ salts with an identical anion component had a comparable effect on plant growth: nitrates strongly stimulated plant growth, and chloride treatment resulted in slight but significant growth reduction, but plants treated with nitrites and carbonates died within 4 and 5 weeks after the full treatment, respectively. The shoot growth of R. sceleratus plants was relatively insensitive to treatment with Mn, Cd and Zn in the form of sulphate salts, but Pb nitrate increased it. Hyperaccumulation threshold concentration values in the leaves of R. sceleratus were reached for Cd, Pb and Zn. R. sceleratus can be characterized as a shoot accumulator of heavy metals and a hyperaccumulator of Na⁺. A relatively short life cycle together with a high biomass accumulation rate makes R. sceleratus useful for dynamic constructed wetland systems aiming for the purification of concentrated wastewaters.

Keywords: Ranunculus sceleratus; heavy metals; ion accumulation; nitrophily; phytoextraction potential; salinity tolerance.

Figure 1

Relative effect of Na⁺ (in a form of NaCl) in substrate on growth of Ranunculus sceleratus plants. Plants were cultivated for 5 weeks after the full treatment. Data are means from 5 replicates ± SE. Asterisks indicate statistically significant difference from control (p < 0.05).

Figure 2

Effect of Na⁺ (in a form of NaCl) on relative dry mass distribution in Ranunculus sceleratus plants. Plants were cultivated for 5 weeks after the full treatment.

Figure 3

Accumulation of Na⁺ (A) and K⁺ (B) in different parts of Ranunculus sceleratus plants dependent on concentration of Na⁺ (in a form of NaCl) in a substrate. Plants were cultivated for 5 weeks after the full treatment. Data are means from 5 replicates ± SE. Dotted lines in B indicate control values.

Figure 4

Changes in K⁺: Na⁺ molar concentration ratio (A) and electrical conductivity (B) in different parts of Ranunculus sceleratus plants dependent on concentration of Na⁺ (in a form of NaCl) in a substrate. Plants were cultivated for 5 weeks after the full treatment. Data are means from 5 replicates ± SE.

Figure 5

Effect of different Na and K salts on growth of shoots (A) and roots (B) of Ranunculus sceleratus plants. *, roots were decayed. Plants were cultivated for 5 weeks after the full treatment. Data are means from 5 replicates ± SE. Different letters indicate statistically significant differences between treatments (p < 0.05).

Figure 6

Effect of different Na and K salts on accumulation of Na⁺ (A) and K⁺ (B) in different parts of Ranunculus sceleratus plants. Plants were cultivated for 5 weeks after the full treatment. Data are means from 5 replicates ± SE. Different letters indicate statistically significant differences between treatments (p < 0.05).

Figure 7

Effect of different Na and K salts on accumulation of K⁺:Na⁺ molar concentration ratio (A) and electrical conductivity (B) in different parts of Ranunculus sceleratus plants. Plants were cultivated for 5 weeks after the full treatment. Data are means from 5 replicates ± SE. Different letters indicate statistically significant differences between treatments (p < 0.05).

Figure 8

Effect of increasing concentration of heavy metals in substrate (in a form of MnSO₄, CdSO₄, ZnSO₄ and Pb(NO₃)₂) on shoot (A) and root (B) dry mass of Ranunculus sceleratus plants. Plants were cultivated for 5 weeks after the full treatment. Data are means from 5 replicates ± SE. Asterisks indicate statistically significant (p < 0.05) differences from control.

Figure 9

Effect of increasing concentration of Cd (A), Mn (B), Pb (C) and Zn (D) in substrate on accumulation of heavy metals in different parts of Ranunculus sceleratus plants. Plants were cultivated for 5 weeks after the full treatment. Data are means from 3 samples ± SE. Dashed line indicates threshold level of hyperaccumulation for the respective heavy metal.

Figure 10

Effect of increasing concentration of Pb in substrate in a form of acetate or nitrate on shoot (A) and root (B) dry mass of Ranunculus sceleratus plants. Plants were cultivated for 7 weeks after the full treatment. Data are means from 5 replicates ± SE. Different letters indicate statistically significant differences between treatments (p < 0.05).

Figure 11

Effect of increasing concentration of Pb in substrate in a form of nitrate (A) or acetate (B) on accumulation of Pb in different parts of Ranunculus sceleratus plants. Plants were cultivated for 7 weeks after the full treatment. Data are means from 3 samples ± SE. Dashed line indicates threshold level of hyperaccumulation for Pb.