Plant growth-promoting bacterium Pseudomonas sp. strain GRP3 influences iron acquisition in mung bean (Vigna radiata L. Wilzeck)

Siderophores produced by Pseudomonas sp. may be used by the bacteria (homologously) or in effecting plant nutrition (heterologously). The problem of iron non-availability particularly in calcareous soils may be overcome by incorporation of siderophore producing strains of fluorescent psuedomonads (FLPs). Siderophore producing bacterium Pseudomonas strain GRP₃ was used in a pot experiment to assess the role of microbial siderophores in the iron nutrition of mung bean (Vigna radiataL. Wilzeck) using Fe-citrate, Fe-EDTA and Fe(OH)₃ in different concentrations with Hoagland's solution. After 45 days, the plants showed a reduction of chlorotic symptoms and enhanced chlorophyll level in GRP₃ bacterized plants. Bacterization with GRP₃ increased peroxidase activity and lowered catalase activity in roots. In 10 μM Fe-citrate alongwith GRP₃ treatment, chlorophyll a, chlorophyll b and total chlorophyll contents increased significantly by 34, 48 and 39%, respectively, compared to the control. Peroxidase activity in the same treatment was increased by 82% whereas catalase activity decreased by 33%. There was also a significant increase in total and physiologically available iron. A closely similar pattern was observed in chlorophyll content and peroxidase activity in Fe-EDTA and Fe(OH)₃ treated plants; catalase activity was an exception. The data suggests operation of heterologous siderophore uptake system in mung bean in presence of GRP₃. Such siderophore producing system has the potential of improving iron availability to plants and reduce fertilizer usage.     

Effects of Nickel on Growth and Composition of Metal Micronutrients in Barley Plants Grown in Nutrient Solution

Abstract

A hydroponic experiment was conducted in a phytotron at pH 5.5 to study the effects of nickel (Ni) on the growth and composition of metal micronutrients, such as copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn), of barley (Hordeum vulgare L. cv. Minorimugi). Four Ni treatments were conducted (0, 1.0, 10, and 100 μM) for 14 d. Plants grown in 100 μM Ni showed typical visual symptoms of Ni toxicity such as chlorosis, necrosis of leaves, and browning of the root system, while other plants were free from any symptoms. Dry weights were the highest in plants grown in 1.0 μM Ni, with a corresponding increase in the chlorophyll index of the plants, suggesting that 1.0～10 μM Ni needs to be added to the nutrient solution for optimum growth of barley plants. The increase of Ni in the nutrient solutions increased the concentrations of Cu and Fe in roots, while a decrease was observed in shoots. The concentrations of Mn and Zn in shoots and roots of plants decreased with increasing Ni supply in the nutrient solution. Shoot concentrations of Cu, Fe, Mn, and Zn in plants grown at 100 μ M Ni were below the critical levels for deficiency. Plants grown at 1.0 μ M Ni accumulated higher amounts of Cu, Fe, Mn and Zn, indicating that nutrient accumulation in plants was more influenced by dry weights than by nutrient concentrations. The translocation of Cu and Fe from roots to shoots was repressed, while that of Mn and Zn was not repressed with increasing Ni concentration in the nutrient solution.     

Ecology of Arthrobacter JG-9-detectable hydroxamate siderophores in soils

Arthrobacter JG-9-detectable hydroxamate siderophores were monitored in a series of soils subjected to different treatments in the laboratory and in a series of field soils subjected to different regimes. Concentrations of soil siderophores were found to be strongly related to the quantity of organic substrates available for microbial growth in the soil. It was possible to specifically stimulate siderophore production using L-ornithine as a precursor. Soil pH, water activity and iron availability also influenced the production of siderophores in soil. For two series of field samples, siderophores concentration in soil was correlated with grass production. A model is proposed in which the rhizosphere constitutes the most important microsite in soil for siderophore production. Siderophores are thereby conceived as vehicles for iron, increasing the mass flow of iron from the soil-humus complex to the growing microbial, particularly fungal, biomass.     

Environmental Impact on an Arctic Soil–Plant System Resulting from Metals Released from Coal Mine Waste in Svalbard (78° N)

Impact of acid mine drainage (AMD) from a coal mine waste rock pile deposited within a permafrost-affected Arctic ecosystem was investigated near Longyearbyen (Svalbard, 78° N). Analyses included metal concentrations (Al, Fe, Mn, Zn, Ni, Cr, As and Pb) in runoff, soil and plants. It was observed that impacts of AMD, such as plant degradation, were similar to impacts reported from non-arctic ecosystems. It was found that bio-available metal concentrations in soil samples were not useful in assessing potential plant toxicity, as metals were not accumulated in the most impacted area due to low soil pH (pH?<?4). Native graminoid plants in the high impacted area showed accumulation of all the investigated elements. Al, Mn and As were found at phyto-toxic concentrations. Metal uptake in two native graminoid plants was studied in the laboratory. Positive correlations were noted between metal concentrations and plant uptake for all metals investigated, except Fe. High Fe concentrations found in plant samples in the impacted area are considered a result of Fe-oxide precipitation (plaque) on leaves during the spring flush when runoff covers the plants. We conclude that the weathering products Al, Mn and Fe induce the largest negative impact on vegetation in the area, and that a major fraction of the annual uptake of metals occurs during spring flushes. During these flushes, metals produced from weathering processes throughout the winter are released in high concentrations, coinciding with low pH values, low infiltration rates due to permafrost and the start of the plant growth season.     

Atmospheric deposition of heavy metals in central Ontario

As part of a study to determine the magnitude of atmospheric inputs of materials into the lakes of central Ontario, a four-station network of bulk deposition and wet-only precipitation samplers was established in the Muskoka-Haliburton and Sudbury regions to determine the deposition (mg m^2? yr^?1) and volume weighted concentration (μg 1^?1) of Ph, Cu, Ni, Zn, Al, Mn and Fe in precipitation. Large temporal variations in the monthly deposition of all metals were observed. The variations for Cu and Ni exhibited seasonal patterns which could be attributed to a combination of source and wind direction factors. Concentration and deposition of all metals at Muskoka-Haliburton were generally as low or lower than median North American values from the literature. At Sudbury, the large local smelting industry contributed to the elevated Cu, Ni, Zn, and Fe deposition measured in the region (up to two orders of magnitude larger than Muskoka-Haliburton); Al and Mn values were not elevated. Deposition of Cu. Ni and Fe was inversely related to distance from the largest point source at Sudbury. The importance of dry deposition is greatest at Sudbury where dry inputs of Cu, Zn, Al, and Fe generally exceed wet inputs. In contrast, wet deposition of metals at Muskoka-Haliburton predominates over dry. Calculation of an enrichment factor (normalized against Mn) showed that the levels of Pb, Cu, Ni and Zn observed in the precipitation of central Ontario require an additional non-crustal source (either natural or anthropogenic) for explanation.     

Plant heavy metal concentrations and soil biological properties in agricultural serpentine soils

Abstract

Soils developed on serpentinitic rocks have serious limitations for agriculture. They have high levels of magnesium (Mg) and heavy metals [copper (Cu), manganese (Mn), nickel (Ni), and chromium (Cr)] and are deficient in some macronutrients. In parts of Northwestern Spain, serpentine soils have been subjected to intensive management, based on the use of manure and harvesting residues. Although these practices have allowed the growth of crops, plants may have accumulated high amounts of metals. This study was carried out to assess the effect of the management practices on the uptake of heavy metals by crops, and to analyze the relationship between the concentrations of these metals in plants, and soil properties. Moderate levels of Ni and Mn and low levels of Cr and Cu were found in soil extractable fractions of these metals. In spite of this, analysis of plant tissues revealed high levels of Cr and Ni and moderate contents of Mn. Concentrations of Mn and Ni in foliage were correlated to soil extractable contents, whereas simple linear regression between concentration of Cr in plants and the soil‐extractable Cr showed a poor relationship, possibly because the availability of this metal, as Cr(VI), is determined by temporal environmental conditions. To assess the effects of the management on the uptake of heavy metals by plants, a complementary bioassay experiment was carried out in the laboratory in which Festuca rubra and Agrostis stolonifera were sown on serpentine soil with low organic matter content, and amended with peat and/or lime. This experiment confirmed that there is a reduction in heavy metal concentration in plants after organic amendment and suggested that the lower metal availability is partly due to the higher soil microbial activity, produced as a consequence of addition of organic matter.     

Patterns of effects of arbuscular mycorrhizal fungi on plants grown in contaminated soil

Arbuscular mycorrhizal fungi (AMF) are integral functioning parts of plant root systems and are widely recognized for enhancing plant growth on severely disturbed sites, including those contaminated with heavy metals. However, the generality of detailed patterns observed for their influence on various metals and oxidative‐stress parameters in multiple plant species is not clarified. The goal of this study was to investigate the patterns of metal‐stress alleviation by AMF in four plant species. For this purpose, clover, sunflower, mustard, and phacelia were inoculated with Glomus intraradices and compared to noninoculated plants grown under heavy metal–stressed conditions. The study focused on the effect of AMF inoculation on plant biomass, assimilating pigments, total protein, superoxide dismutase and peroxidase activity, lipid peroxidation and As, Cd, Co, Cu, Fe, Mn, P, Pb, U, and Zn contents. As a result of inoculation very different patterns of variation were obtained for concentrations of elements and for biochemical parameters in plants. The particular effect of AMF inoculation on plants was species‐ and metal‐specific, although there was a general enhancement of plant growth.     

Effect of wastewater irrigation on mineral com‐position of corn and sorghum plants in a pot experiment

Effect of wastewater irrigation was investigated on mineral composition of corn and sorghum plants in a pot experiment. The ranges for the concentration of different minerals in corn plants were 0.67–0.89% calcium (Ca), 0.38–0.58% magnesium (Mg), 0.09–1.29% sodium (Na), 0.81–1.87% nitrogen (N), 1.81–2.27% potassium (K), 0.12–0.16% phosphorus (P), 190–257 mg/kg iron (Fe), 3.5–5.6 mg/kg copper (Cu), 37.1–44.5 mg/kg manganese (Mn), 21.6–33.6 mg/kg zinc (Zn), 1.40–1.84 mg/kg molydbenum (Mo), 11.0–45.7 mg/kg lead (Pb), and 2.5–10.8 mg/kg nickel (Ni). Whereas for sorghum plants, the ranges were: 0.56–0.68% Ca, 0.19–0.32% Mg, 0.02–0.27% Na, 0.69–1.53% N, 1.40–1.89% K, 0.10–0.14% P, 190–320 mg/kg Fe, 3.8–6.0 mg/kg Cu, 29.2–37.6 mg/kg Mn, 21.1–29.9 mg/kg Zn, 2.2–3.7 mg/kg Mo, 12.3–59.0 mg/kg Pb, and 2.5–15.2 mg/kg Ni. Heavy metals such as cobalt (Co) and cadmium (Cd) were below detection limits at mg/kg levels. The concentrations of Ca, N, K, P, Cu, and Mn in corn plants were in the deficient range except for Mg, Fe, Zn, and Al. The concentrations of Ca, N, P, K, Cu, Mn, Mg, and Zn in sorghum plants were in the deficient range except for Fe and aluminum (Al). The analysis of regression indicated a strong interaction between Pb, Ni, Ca, and Fe in corn and sorghum plants. In conclusion, waste water irrigation did not increase mineral concentrations of either macro‐ and micro‐elements or heavy trace metals in corn and sorghum plants to hazardous limits according to the established standards and could be used safely for crop irrigation.     

Evaluation of Trace Element Pollution from Vehicle Emissions in Petunia Plants

Effects of environmental pollution from road traffic on traceelement accumulation and deposition were examined in washed andunwashed petunia leaves. The plants were grown in an urban and ina suburban area. Substantial amounts of elements were removedsimply by washing with demineralised water, which removed atleast 45% of Al, Fe and Pb and 15% of Mn, Cu and Zn in urbanareas, where the aerial deposition took place. Throughout thegrowing season, the concentrations of Fe, Cu, Al, Ni and Pbincreased in the washed leaves of the petunia plants grown inurban areas. However, the plant very specifically controlled thecontents of Mn and Zn. Concentrations of elements were significantly higher in washed leaves from the urban area thanthose from the surburban area, indicating that this ornamentalplant is able to absorb Fe, Al, Ni and Pb through its root andleaves. Periodic assessment of the accumulation of traceelements in urban areas with intense traffic is important inorder to evaluate the rate of environmental pollution.     

Uptake and translocation of iron from ferrated rhodotorulic acid in tomato

Micro‐organisms may develop an iron‐deficiency stress when grown in an alkaline environment and secrete ferric‐specific chelators known as siderophores. Some of these siderophores may have stability constants which can exceed 30. This is comparable to the synethetic Fe chelate FeEDDHA. Our objective was to determine if the Fe‐efficient T3238 FER tomato and the Fe‐inefficient T3238 fer tomato could use iron supplied as the siderophore ferrated‐rhodotorulic acid. After these two tomato cultivars were grown with adequate nutrition to obtain plants large enough for experimental testing, they were grown without iron until Fe‐deficiency‐stress symptoms developed and then iron was supplied as ferrated‐rhodoturulic acid. Iron efficient T3238 FER tomato utilized iron supplied as the siderophore and greened whereas, the Fe‐inefficient T3238 fer tomato plants were chlorotic because they could not use the iron in the siderophore. This study demonstrated that some higher plants subjected to various degrees of iron‐deficiency stress in nutrient culture may derive their iron requirement from siderophores of microbial origin.     

Distribution of rare-earth (Y,La, Ce) and other heavy metals in the profiles of the podzolic soil group

Along with Fe and Al, many heavy metals (Mn, Cr, Zn, Cu, and Ni) show a markedly pronounced eluvial-illuvial redistribution in the profiles of soils of the podzolic group. The intensity of the redistribution of the bulk forms of these metals is comparable with that of Fe and exceeds that of Al. Although the podzolic soils are depleted of rare-earth metals, the latter respond readily to soil podzolization. The inactive participation of Al is explained by an insignificant portion of the active reaction-capable fraction. Podzolization does not influence the profile distribution of Sr and Ba. The leaching degree of heavy metals such as Mn, Cr, Zn, Ni, and Zr is noticeably higher in the sandy podzols than in the loamy podzolic soils. Leaching of heavy metals from the podzolic horizons is of geochemical importance, whereas the depletion of metals participating in plant nutrition and biota development is of ecological importance. The leaching of heavy metals is related to the destruction of clay particles in the heavy-textured podzolic soils; the effect of the soil acidity on the leaching of heavy metals is less significant.     

Wet Deposition of Trace Metals in Singapore

The concentrations of 12 trace metals (Al, Cd, Cr, Cu, Co, Fe,Mn, Ni, Pb, Zn, V, and Ti) in wet depositions are reported. Eighty four rainwater samples were collected using an automated wet-only sampler in Singapore for one year (2000) and subjected to chemical analysis using ICP-MS. Based on the volume-weighted meanconcentrations measured, the trace metals were classified into three groups: Al and Fe with an average concentration of largerthan 15 μg L^-1, Cr, Cu, Mn, Ni, Pb, Zn, V, and Ti withconcentrations between 1 and 10 μg L^-1, and finally Co and Cd with concentrations lower than 1 μg L^-1. Elementenrichment factors were calculated to distinguish between naturaland anthropogenic sources. The calculation of crustal enrichmentfactors with Al as the reference element indicated that while Ti,Fe and Mn originated from crustal sources, the remaining trace metals (Cd, Cr, Co, Cu, Ni, Pb, Zn and V) were mainly derived from anthropogenic sources. The removal of the trace metals from the atmosphere by precipitation was influenced by the rainfall amount as well as pH. The magnitude of the measured average annual wet deposition fluxes of Al, Fe, and combustion-generatedelements such as V, Ni, and Cu is higher than that reportedfor other sites outside Singapore, owing to abundant rainfallthroughout the year in this region.     

Enhanced Heavy Metal Phytoextraction from Marine Dredged Sediments Comparing Conventional Chelating Agents (Citric Acid and EDTA) with Humic Substances

Metal (Cu, Mn, Ni, Zn, Fe) concentrations in marine sediment and zooplankton were investigated in Izmir Bay of the Eastern Aegean Sea, Turkey. The study aimed to assess the levels of metal in different environmental compartments of the Izmir Bay. Metal concentrations in the sediment (dry weight) ranged between 4.26–70.8 μg g^?1 for Cu, 233–923 μg g^?1 for Mn, 14.9–127 μg g^?1 for Ni, 25.6–295 μg g^?1 for Zn, 12,404–76,899 μg g^?1 for Fe and 38,226–91,532 μg g^?1 for Al in the Izmir Bay. Maximum metal concentrations in zooplankton were observed during summer season in the inner bay. Significant relationships existed between the concentrations of certain metals (Al, Fe, Mn and Ni) in sediment, suggesting similar sources and/or similar geochemical processes controlling such metals. Higher concentrations of Cu, Zn and percent organic matter contents were found in the middle-inner bays sediments. Based on the correlation matrix obtained for metal data, organic matter was found to be the dominant factor controlling Cu and Zn distributions in the sediment. In general, mean Cu and Zn levels in the bay were above background concentrations in Mediterranean sediments. Zooplankton metal concentrations were similar to sediment distributions.     

Cyanide effects on transport of trace metals in plants

Abstract

Cyanide at levels of 50 to 100 μg NaCN/g soil was not only toxic to bush bean plants, but also resulted in increased uptake of Cu, Co, Ni, Al, Ti, and, to a slight extent, of Fe. Either the phytotoxicity from the cyanide or the metals resulted in increased transport of Na to leaves from roots. In studies with ¹⁴C‐cyanide the transport of some cyanide into plants and to leaves simultaneously with the metals was demonstrated. There was a root, stem, leaf gradient for ¹⁴C. From solutions, cyanide resulted in increased plant uptake somewhat of Cu, Zn, and Fe. The results have bearing on the use of cyanide as a metabolic inhibitor as well as on phytotoxicities of metals.     

Bulk sediment bioassays with five species of fresh-water oligochaetes

The fluxes of metals (Na, K, Ca, Mg, Fe, Mn, Al, Cu, Zn, Pb, Cd, Cr, and Ni) in two spruce forest soils in S. Sweden were quantified using the lysimeter technique. Amounts in precipitation (dry and wet), throughfall, litterfall and annual accumulation in biomass were also quantified, as well as stores in soil and biomass. The metal concentrations of the soil solutions varied greatly according to season. The leaching of some metals (Fe, Cu, Pb, Cr, and organic forms of Al) was associated with the leaching of organic matter. These complexes were leached from the A horizon in considerable amounts. They were precipitated in the upper B horizon and only small amounts were transported further downward. By contrast, the leaching of Na, Mg, Ca, Mn, Cd, Zn, Ni, and inorganic forms of Al increased with increasing soil depth. The concentrations of these metals also increased with increasing soil solution acidity. The highest concentrations were often found at the transition to the C horizon. The amounts of Na, K, Mg, Ca, Mn, Al, Zn, Cd, Cr, and Ni leached from the rooting zone were found to be larger than the amounts deposited from the atmosphere, the main source of these metals being the mineral soil. The reverse was true of Ph, Cu, and Fe, the sink being the upper part of the B horizon.     

Plant tolerance to nickel toxicity: II nickel effects on influx and transport of mineral nutrients in four plant species

Nickel (Ni) is an essential micronutrient for higher plants but is toxic to plants at excess levels. Plant species differ extensively for mineral uptake and accumulation, and these differences often help explain plant tolerances to mineral toxicities/deficiencies. Solution culture experiments were conducted under controlled conditions to determine the effects of Ni on influx into roots (IN) and transport from roots to shoots (TR) of zinc (Zn), iron (Fe), copper (Cu), manganese (Mn), calcium (Ca), magnesium (Mg), phosphorus (P), and sulfur (S) in white clover (Trifolium repens L.), cabbage (ßrassica oleracea van capitata L.), ryegrass (Lolium perenne L.), and maize (Zea mays L.). Nickel decreased both IN and TR of Zn, Cu, Ca, and Mg, but only TR of Fe and Mn in white clover. Both IN and TR of Cu, Fe, Mn, Mg, and S were markedly decreased by Ni >30 μM in cabbage, whereas IN and TR of P increased with Ni treatment. For ryegrass, TR of Cu, Fe, Mn, Ca, and Mg was decreased, but IN of these elements except Mg was not affected by Ni. The IN and TR of P and S were increased in ryegrass with increasing external Ni levels. Nickel inhibited IN of Cu, Ca, and Mg, and TR of Zn, Cu, Fe, Mn, Ca, and Mg in maize. Plant species differed in response to Ni relative to IN and TR of mineral nutrients. Plant tolerance to Ni toxicity was associated with the influence of Ni on IN and TR of Cu, Fe, and Mn in white clover and cabbage but not in maize and ryegrass.     

Metals in stocked Lake Trout (Salvelinus namaycush) in lakes near Sudbury,Canada

Muscle tissue from stocked lake trout (Salvelinus namaycush) from lakes near the smelters at Sudbury, Canada was analyzed for Al, Cu, Fe, Hg, Mn, Ni, and Zn. Metals in tissue were not abnormally high compared with fish from lakes farther away from the smelters. Tissue concentrations of Al, Fe, Mn, and Zn declined significantly after stocking. Because metal concentrations were lower in hatchery water than the study lakes, this decline in tissue metal suggests that diet plays a prominent role in the uptake of these metals in lake trout. Only Hg showed evidence of accumulation to levels that might be harmful for human consumption, and then only in a few older, larger trout. In contrast, tissue Mn and Zn were inversely correlated with trout weight. Fluctuations, independent of age, body weight or time of year, were observed in tissue concentrations of Al, Cu, and Zn. Annual cycles, independent of pH and alkalinity were observed in tissue concentrations of Fe, Hg, Mn, and Ni. Bioaccumulation of metal proved to be an unfounded concern for the rehabilitation of fish populations in lakes near Sudbury.     

Metal concentrations,growth, and yield of potato produced from In Vitro plantlets or microtubers and grown in municipal solid‐waste‐amended substrates

In vitro plantlets or microtubers (in vitro produced tubers) of ‘Spunta’ potato (Solanum tuberosum L.) were planted in a 3 soil: 2 peat moss: 1 sand substrate (by volume) amended with municipal solid waste (MS W) compost at 0, 10, 20, or 30 g 4^‐1 L pot. Three months later, plant growth and tuber yield were evaluated and concentrations of shoot and tuber tin (Sn), arsenic (As), copper (Cu), zinc (Zn), nickel (Ni), lead (Pb), manganese (Mn), cadmium (Cd), and iron (Fe) were determined. Amending with MSW resulted in significant increases in concentrations of all tested metals in the substrate. Number of proliferated shoots of plants started from rooted plantlets was greatest at 10 g pot^‐1 MSW, whereas shoot weight of plants started from microtubers was greatest at 10 and 20 g pot^‐1 MSW. Tuber yield of plants started from rooted plantlets or microtubers was greatest at 10 or 30 g pot^‐1 MSW, respectively. In all instances, amending with MSW at 30 g pot^‐1 resulted in significant increases in concentrations of all tested metals in shoots and tubers. Concentrations of shoot Ni and tuber Zn and Fe for plants started from rooted plantlets and concentrations of shoot Fe and tuber As, Cu and Pb for plants started from microtubers increased consistently with increasing MSW percentage of the substrate. Plants started from rooted plantlets produced shoots with sufficient Zn, Mn, and Ni concentrations regardless of the substrate but with toxic Cu content at 30 g pot^‐1 MSW. Plants started from microtubers produced shoots with sufficient Mn and Ni concentrations regardless of the substrate but with low Zn and deficient Cu in unamended substrates. All plants had shoot Fe content higher than the sufficiency range. Although there were significant differences in concentrations of some nutrients among MSW treatments, no symptoms of nutrient toxicity or deficiency were observed. In all instances, tested elements did not accumulate in tubers to levels hazardous to human health. Concentrations of Cd, the most hazardous element, in potato tubers was not high enough to pose a threat to human. Our results indicate that there is a potential use of MSW in satisfying the needs of potato growth with negligible increases in heavy metal concentrations in tubers.     

A mass-balance analysis of trace metals in two weedbeds

A mass-balance approach was used to examine the role of macrophyte beds as a sink or source for 7 metals over time scales varying from two months (the growing season of the plants) to one year. During the growing season the macrophyte beds were found to be net sinks for particulate metals but were net sources of dissolved metals. During senescence, ca. 15–20% of the Al, Fe, and Mn and ca. 25–30% of the Cr, Cu, Ni and Zn within the macrophyte tissues at maximum seasonal biomass was lost to the surrounding waters in a dissolved form. The export of metals from the weeds during senescence was a very small fraction (<0.01% of Al, Fe to 3.5% of Zn) of the annual allochthonous metal loading to Fitch Bay in L. Memphremagog, Quebec. In L. Weedon however, metal export during senescence was 34% (Mn) to 57%(Cu) of the annual allochthonous load. The time estimated for the plants to recycle the metals within the rooting zone of the sediments was on the order of hundreds of years. These results demonstrate that while weedbeds are net sources of metals during the summer, only a small fraction of metals in littoral sediments are not permanently buried over the longer term.     

Chemical analysis of Teucrium species (Lamiaceae) growing on serpentine soils in Bulgaria

Trace elemental concentrations (Fe, Ni, Mn, Cr, Co, Cu, Zn, Pb, Cd, and As) in aerial biomass (stems, leaves, and flowers) of the medicinal plants Teucrium chamaedrys, T. montanum, and T. polium growing on serpentine soils in Bulgaria were examined in relation to the total element contents in their respective rhizospheric soils. The objectives of the study were to evaluate: (1) elemental concentrations in plant tissues and associated soil samples together with the plants ability to tolerate/accumulate metal concentrations; (2) correlations between total metal concentrations in plants and their rhizospheric soils. Metal concentrations varied across species and sites. Their levels in plant tissues from nonserpentine sites were always lower compared to those from serpentine ones. The highest concentrations for Fe, Ni, Mn, Cr, As, Cu, and Pb were found in T. polium. Positive correlation coefficients were established between Ni, Cr, Fe, Co, and Cu in plants and Ca in the soil. None of the species tested hyperaccumulated metals although the metal concentration in some of them exceeded the range naturally found in plants. The Teucrium species can be considered as “excluders”, containing relatively low metal concentrations in their aerial parts (stems, leaves, and flowers) even in cases of high elemental concentrations in the rhizospheric soil. In all three medicinal plants, metal concentrations for toxic elements were above the permissible limits for pharmaceutical purposes. Therefore, plants found on serpentine bedrock are not recommended to be collected for pharmaceutical purposes.