3.2. Manganese in native plants
The mean Mn levels of the roots and shoots of the studied plants are 469 and 430 ppm, respectively. However, the maximum and minimum values of Mn in the studied plants are 2864 and 18.2 ppm in the roots and 3612 and 6.5 ppm, respectively, in the shoots.
The mean
Alyssum saxatile (AL)’s soil, root, and shoot values for Mn are 328, 260, and 173 ppm, respectively (
Figure 2;
Table 1). The Mn values in AL’s soils is greater than the shoot and root values, with the respective maximum and minimum Mn values of AL changing between 305 and 86 ppm for the roots and between 261 and 113 ppm for the shoots. These levels are much higher than Mn content of the reference plant (200 ppm) suggested by Pais & Jones [
33]. The ECS and ECR of Mn for AL’s shoots and roots are given, respectively, as 0.59and 0.90, and are lower than their soil values. The AL’s TLFs for Mn are between 0.20 and 2.66 (mean: 1.12). The values indicate that AL is a good plant for the bioaccumulation of Mn because the ECRs and ECSs values are close to 1.
The mean Mn levels in
Anchusa arvensis’s (AN) soil, roots, and shoots are, respectively, 1096, 1347, and 1936 ppm (
Figure 2;
Table 1). The average values of ECS and ECR for Mn are, respectively, 1.65 and 1.38. The AN’s TLF was observed to be between 0.93 and 1.13 (mean: 1.03) (
Figure 3;
Table 1). These values show that AN is very well plant to bioaccumulate Mn due to higher ECS and ECR>1.
The average
Centaurea cyanus (CE)’s soil, root, and shoot values are, respectively, 122, 97, and 218 ppm (
Figure 2;
Table 1). The average value of soils for Mn is lower than the average of shoot and higher than the average of root (p < 0.05). The ECS is 1.56 higher than 1, but ECR is 0.81 lower than 1. These parameters indicate that
C.
cyanus can use in the phytoremediation studies of Mn due to higher ECS than 1 (
Figure 3;
Table 1).
The mean soil, roots, and shoots values of the
Carduus nutans (CR) for Mn are, respectively, 36, 158, and 134 ppm. The mean Mn concentrations of CR’s root and shoot are greater than that in the soil. The mean ECR, ECS, and TLF for Mn in CR are 4.35, 4.04, and 1.44, respectively (
Figure 3;
Table 1). These results indicate that CR can be useful in the phytoremediation studies of Mn due to higher ECS and ECR than 1.
The mean soil, root, and shoot values of
Cynoglossum officinale (CY) for Mn are, respectively, 27, 31, and 39 ppm. The average Mn values of soils are lower than that in the CY’s shoot and root. The average values of CY’s ECR, ECS, and TLFs are 1.18, 1.13 and 1.00, respectively (
Figure 3;
Table 1). These parameters indicate that CY’s shoot can be good plant to bioaccumulate Mn due to higher ECS and ECR than 1.
The mean
Glaucium flavum’s (GL) soil, roots, and shoots values are, respectively, 175, 2576, and 1920 ppm for Mn. The mean GL’s ECR, ECS, and TLF are, 14.8, 11.05, and 0.75, respectively for Mn(
Figure 3;
Table 1). These results show that GL is very well plant for the accumulation of Mn in mining areas.
The average
Isatis (IS)’s soil, root, and shoot contents for Mn are 97, 168, and 196 ppm, respectively (
Figure 2;
Table 1). The Mn values in IS soil are lower than those in shoots and roots. The mean ECR, ECS, and TLFs of IS for Mn are 2.16, 2.70, and 0.95, respectively (
Figure 2;
Table 1). The IS’s ECS, ECR, and TLFs for Mn show that
Isatis is useful plant for the phytoremediation studies of Mn (
Figure 3;
Table 1).
The mean
Onosma’s (ON) soil, root, and shoot values are, respectively, 115, 124, and 364 ppm (
Figure 2;
Table 1). The mean Mn levels of ON soils are lower than in ON’s shoot and root. The mean ECR and ECS values for Mn are 1.06 and 2.92, respectively (
Figure 3;
Table 1). These values show that the root and shoot of ON accumulate very well Mn from the soil as seen for Se (Sasmaz et al., 2015).
The average
Phlomis (PH)’s soil, root and shoot concentrations are, respectively, 214, 357, and 263 ppm, respectively for Mn. The mean PH’s ECR, ECS, and TLF for Mn are, respectively, 4.00, 3.49, and 1.03 ((
Figure 3;
Table 1). The ECR and ECS values are greater than 1 (except for PH-04 sample), which shows that the PH root and shoot could be useful for cleaning or rehabilitating of soils polluted by Mn as seen for Se [
32].
The mean
Silene compacta L. (SL)’s soil, root, and shoot values are, respectively, 281, 172, and 177 ppm (
Figure 2;
Table 1). The mean Mn values of SL’s soil are higher than in both SL shoots and roots, except for three samples. The mean ECR, ECS and TLF of SL is higher than 1 for three samples (p < 0.05), but they are lower than 1 for three samples ((
Figure 3;
Table 1).). These parameters indicate that SL cannot use as a bioaccumulator plant for Mn.
The average
Verbascum thapsus L. (VR)’s soil, root, and shoot values are, respectively, 221, 469, and 430 ppm for Mn (
Table 1). The mean soil values of VR are lower than the mean Mn concentrations in the shoots and roots (p<0.05) (
Table 1). The mean ECR and ECS values are 11.03 and 7.03, respectively, greater than 1 (
Figure 3;
Table 1), which indicates that
V. thapsus is very well plant for phytoremediation of soils contaminated by Mn.
According to Kabata-Pendias [
2], the composition of the wall rock was the primary indicator of the Mn level in the soil. The manganese concentrations of global soils range from 411 to 550 ppm across these soil samples. In calcareous and loamy soils, it is present at the highest quantities. The typical Mn content of soil varies globally, ranging to 525 ppm (in Cambisols) from 270 ppm (in Podzols). The mean for soils worldwide is 488 ppm, whereas the computation for soils in the United States is 495 ppm. In Finnish soils, the 90th percentile of the total Mn concentration is 600 ppm, whereas the level of acid-soluble Mn is 280 ppm. The median Mn values in Lithuanian soils depending on the kind of parent material range from 245 ppm in those derived from eolian sediments to 605 ppm in those derived from loamy clay glacial deposits. Australia’s soils generated from basalts and andesites have been found to have the greatest Mn content, up to 9200 ppm. In numerous additional soils from different nations, mostly belonging to the Cambisols group, the concentration of Mn can reach up to 4000 ppm, with an average falling between 800 and 1000 ppm. Certain top soils in the Slovak Republic have been observed to have high Mn concentrations, up to 8510 ppm [
34]. Although Mn has not been found to be a harmful element in soils, its maximal accumulation concentration in agricultural soils is thought to be between 1500 and 3000 ppm. Metal smelting operations, sewage sludge, municipal wastewaters and mining sites are the main human sources of manganese. The fuel additives’ combustion is not as significant. Alluvial soils, however, can accumulate Mn from fuel consumption up to >1000 ppm in some areas (such the Mississippi River Delta) [
35]. Soils in polluted riparian regions can have as much as 2700 ppm of Mn [
36]. Because of the reductive breakdown of Mn oxides, the soluble Mn fraction rises in soils that are irrigated with water impacted by acidic mine waters [
37].
Among plants growing on the same soil, manganese varies notably widely; in
Medicago trunculata, the average is 30 ppm, while in
Lupinus albus, it is almost 500 ppm. Similar to this, reports from many nations indicate that a broad range of Mn has been found in forage plants. Most plants have critical Mn deficiency levels between 15 and 25 ppm, but the hazardous Mn concentration for plants varies greatly depending on soil and plant variables. In general, a Mn level of more than 400 ppm affects the majority of plants. However, for a number of more resistant species or genotypes, the accumulation exceeding 1000 ppm has also frequently been recorded [
35,
36,
38]. According to Peng et al. [
1], the hyperaccumulator plants,
Phytoacca americana, accumulated up to 13,400 ppm of Mn from the polluted soil in their leaves.
Bihanic et al. [
39] and Losfeld et al. [
40] have reported success using
Grevillea meisneri in the restoration of degraded mining sites in New Caledonia and in providing biomass for the synthesis of ecocatalysts. It was observed that transplanted seedlings from nurseries accumulate the same amount of Mn as plants do and store it in the same tissues to produce biomass that is high in Mn. It has been found that Mn can accumulate in the dried leaves of
Alyxia poyaensis and
Denhamia species at amounts more than 1%. These plants were referred to by van der Ent et al. [
41] as “Mn hyperaccumulators”. In a similar vein, many species found in New Caledonia collect manganese at levels between 3,000 and 10,000 ppm.
Based on field study conducted in Mn-rich soils, Min et al. [
38] identified
Phytolacca americana as a new manganese hyperaccumulator plant. This species exhibits exceptional Mn absorption and accumulation capabilities in addition to its amazing tolerance to the element. On the Mn tailings wastelands of Xiangtan, the greatest Mn level in the leaf dry matter was 8000 ppm, with a mean of 6490 ppm. A high translocation factor (>10.76) was found to be characteristic of the species. As external Mn levels grew in nutrient solution cultivation conditions, the concentrations of manganese in the shoots also increased. These species offer a novel plant resource for investigating the process underlying Mn hyperaccumulation and may prove useful in the phytoremediation of soils contaminated with Mn.
The level of Mn in the tissues above ground is consistently higher than that in the roots, according to research by Yang et al. [
42]. Mn levels in the stems and leaves all surpassed 10,000 ppm, the recommended threshold for Mn hyperaccumulation, when the external Mn supply was at high concentrations. A significant 86% of the Mn extracted from the substrates was deposited in the aboveground tissues.
Schima superba is a Mn hyperaccumulator, as these results verified.
Branching and leaves of bilberry (
Vaccinium myrtillus) grown on low-pH (2.77-3.62) soil with high Mn content (490-6277 ppm) were gathered in the Krusne Hory Ore Mountains, Czech Republic. The range of Mn concentration in leaves was 274-11,159 mg kg-1, with a notable rise during the growth season when the leaves dried up early because of the lack of precipitation. The amounts of Mn in the branches of newly sprouted leaves were similar in the years of collection and growth seasons (2062-3885 ppm). It was established that manganese hyperaccumulation occurs in bilberries and that manganese levels rise steadily during the growing seasons. There was a favorable link found between soil moisture content and the manganese level of bilberry leaves [
43].