Cd Phytoavailability Research Articles

Enhancement of arbuscular mycorrhizal fungus (Glomus versiforme) on the growth and Cd uptake by Cd-hyperaccumulator Solanum nigrum

Arbuscular mycorrhizal fungus (AMF) can enhance plant growth and resistance to toxicity produced by heavy metals (HMs), affect the bioavailability of HMs in soil and the uptake of HMs by plants, and thus has been emerged as the most prominent symbiotic fungus for contribution to phytoremediation. A greenhouse pot experiment was conducted to assess the effect of Glomus versiforme BGC GD01C (Gv) on the growth and Cd accumulation of Cd-hyperaccumulator Solanum nigrum in different Cd-added soils (0, 25, 50, 100mgCdkg−1 soil). Mycorrhizal colonization rates were generally high (from 71% to 82%) in Gv-inoculated treatments at all Cd levels. Gv colonization enhanced soil acid phosphatase activity, and hence elevated P acquisition and growth of S. nigrum at all Cd levels. Moreover, the presence of Gv significantly increased DTPA-extractable (phytoavailable) Cd concentrations in 25 and 50mgCdkg−1 soils, but did not affect phytoavailable Cd in 100mgCdkg−1 soil. Similarly, inoculation with Gv significantly increased Cd concentrations of S. nigrum in 25 and 50mgCdkg−1 soils, but decreased Cd concentrations of the plants in 100mgCdkg−1 soil. Overall, inoculation with Gv greatly improved the total Cd uptakes in all plant tissues at all Cd levels. The present results indicated that S. nigrum associated with Gv effectively improved the Cd uptake by plant and would be a new strategy in microbe-assisted phytoremediation for Cd-contaminated soils.

Phytoavailability of cadmium (Cd) to Pak choi (Brassica chinensis L.) grown in Chinese soils: a model to evaluate the impact of soil Cd pollution on potential dietary toxicity.

Food chain contamination by soil cadmium (Cd) through vegetable consumption poses a threat to human health. Therefore, an understanding is needed on the relationship between the phytoavailability of Cd in soils and its uptake in edible tissues of vegetables. The purpose of this study was to establish soil Cd thresholds of representative Chinese soils based on dietary toxicity to humans and develop a model to evaluate the phytoavailability of Cd to Pak choi (Brassica chinensis L.) based on soil properties. Mehlich-3 extractable Cd thresholds were more suitable for Stagnic Anthrosols, Calcareous, Ustic Cambosols, Typic Haplustalfs, Udic Ferrisols and Periudic Argosols with values of 0.30, 0.25, 0.18, 0.16, 0.15 and 0.03 mg kg−1, respectively, while total Cd is adequate threshold for Mollisols with a value of 0.86 mg kg−1. A stepwise regression model indicated that Cd phytoavailability to Pak choi was significantly influenced by soil pH, organic matter, total Zinc and Cd concentrations in soil. Therefore, since Cd accumulation in Pak choi varied with soil characteristics, they should be considered while assessing the environmental quality of soils to ensure the hygienically safe food production.

Impact of emerging and low cost alternative amendments on the (im)mobilization and phytoavailability of Cd and Pb in a contaminated floodplain soil

Contamination of wetland ecosystems by cadmium (Cd) and lead (Pb) is a serious concern because of its high health risk via the food chain. Therefore, an ecological solution is required to effectively remediate contaminated floodplain soils by toxic metals. This study aimed to assess the effects of various emerging amendments (e.g., nano-hydroxyapatite, biochar, chitosan, and organo-clay) and several of low cost amendments (e.g., activated carbon, bentonite, cement kiln dust, fly ash, lime stone, sugar beet factory lime, and zeolite) on the (im)mobilization of Cd and Pb and their uptake by rapeseed (Brassica napus) in a contaminated floodplain soil. Application of the amendments (except for OC, HA, and FA) increased the rapeseed dry biomass yield significantly compared to control. The amendments (except organo-clay and zeolite) decreased soluble+exchangeable Cd (4–60%) compared to the control. Although the cement kiln dust, sugar beet factory lime, and lime stone showed the highest decreasing rate of soluble + exchangeable Cd, they increased the carbonate fraction and Cd in plants, which might be due to dissolving of carbonates and release of Cd in the rhizosphere. The zeolite, bentonite, activated carbon, biochar, and chitosan decreased Cd in plants (22–36%). The amendments (except organo-clay and zeolite) decreased soluble + exchangeable Pb by 6–87% and decreased Pb in the plant by 35–99% compared to the control. The sugar beet factory lime, cement kiln dust, and lime stone showed the highest decreasing rate of soluble Pb and nano-hydroxyapatite showed the highest decreasing rate of Pb uptake which highlights the high potential of these amendments for Pb immobilization in the soil and reduce Pb accumulation by plants.

Field evidence of cadmium phytoavailability decreased effectively by rape straw and/or red mud with zinc sulphate in a Cd-contaminated calcareous soil.

To reduce Cd phytoavailability in calcareous soils, the effects of soil amendments of red mud, rape straw, and corn straw in combination with zinc fertilization on Cd extractability and phytoavailability to spinach, tomato, Chinese cabbage and radish were investigated in a calcareous soil with added Cd at 1.5 mg kg−1. The results showed that water soluble and exchangeable Cd in soils was significantly decreased by the amendments themselves from 26% to 70%, which resulted in marked decrease by approximately from 34% to 77% in Cd concentration in vegetables. The amendments plus Zn fertilization further decreased the Cd concentration in vegetables. Also cruciferous rape straw was more effective than gramineous corn straw. In all treatments, rape straw plus red mud combined with Zn fertilization was most effective in decreasing Cd phytoavailability in soils, and it is potential to be an efficient and cost-effective measure to ensure food safety for vegetable production in mildly Cd-contaminated calcareous soils.

Cadmium phytoavailability in soils and evaluation of extractant effectiveness using an isotope technique

Large areas of land are nowadays contaminated by heavy metals and, it is therefore, important to monitor their levels in soils. Vegetables act as transfer mechanisms of such contaminants from soils to higher levels in the food chain. In this study, we aimed to evaluate the effectiveness of chemical extractants by the L-value method for Cd phytoavailability using the 109Cd radionuclide. In a greenhouse experiment, rocket plants (Eruca sativa L.) were cultivated in pots with samples from Typic Hapludox and Typic Quartzipsamment soils. Cadmium concentrations ranging from 0 to 16 mg kg-1 were added to a 200 mL solution containing 148 kBq 109Cd. The available Cd in the soil was extracted by DTPA, Mehlich-1, Mehlich-3, and a mixture of organic acids (acetic, citric, lactic, and oxalic acids). Cd concentrations were determined by atomic absorption spectrophotometry, and 109Cd radionuclide activity was measured by low-level β-counting. The dry matter yield was not influenced by Cd rates, but the Cd content and accumulation in shoots had a positive linear correlation. Generally, Cd was extracted in higher quantities by Mehlich-1 followed by DTPA, Mehlich-3, and organic acids. A linear correlation was found between the chemical extractants and Cd accumulation in shoots for both soils. According to the L Ratio, the extractants based on strong acids and chelating agents presented low efficiency regarding Cd phytoavailability. The organic acids, which presented values close to the L-value, may provide a promising method for evaluating environmental contaminants.

Effect of pyoverdine supply on cadmium and nickel complexation and phytoavailability in hydroponics.

Siderophores are chelators with a high selectivity for Fe(III) and a good affinity for divalent metals, including Cd(II) and Ni(II). Inoculation with siderophore-producing bacteria (SPB) has thus been proposed as an alternative to chelator supply in phytoremediation. Accurate assessments of the potential of this association require a dissection of the interaction of siderophores with metals at the soil-root interface. This study focuses on pyoverdine (Pvd), the main siderophore produced by Pseudomonas aeruginosa. We first assessed the ability of Pvd to coordinate Ni(II). The stability constant of Pvd-Ni(II) (log K (L'Ni) = 10.9) was found to be higher than that of Pvd-Cd(II) (log K (L'Cd) = 8.2). We then investigated the effect of a direct supply of Pvd on the mobilization, speciation, and phytoavailability of Cd and Ni in hydroponics. When supplied at a concentration of 50 μM, Pvd selectively promoted Ni mobilization from smectite. It decreased plant Ni and Cd contents and the free ionic fractions of these two metals, consistent with the free ion activity model. Pvd had a more pronounced effect for Ni than for Cd, as predicted from its coordination properties. Inoculation with P. aeruginosa had a similar effect on Ni phytoavailability to the direct supply of Pvd.

Distribution of Phytoavailable Heavy Metals in the Korean Agricultural Soils Affected by the Abandoned Mining Sites and Soil Properties Influencing on the Phytoavailable Metal Pools

Absorption and accumulation of heavy metals in plants were determined by phytoavailable contents rather than total contents of heavy metals. Therefore, phytoavailability-based management protocol should be prepared for safe food crop production in contaminated agricultural lands. This study was conducted to understand the distribution and phytoavailability of heavy metal in the Korean agricultural soils affected by abandoned mining sites along with investigation of soil properties (soil pH, OM, DOC, clay content, Al/Fe/Mn content) influencing on the metal phytoavailability. For this, 142 agricultural soils located nearby 39 abandoned mining sites distributed in five province in Korea, were analyzed. Among the four different heavy metals, cadmium (Cd) and zinc (Zn) appeared to exist in more phytoavailable form than cupper (Cu) and lead (Pb). Soil pH was the main factor governing phytoavailable Cd, Pb, and Zn showing positive relationship with partitioning coefficients of the corresponding metals; Cd (r = 0.66, P < 0.001), Pb (r = 0.70, P < 0.001), and Zn (r = 0.62, P < 0.001). This implied higher phytoavailability of the corresponding metals with higher soil pH. In contrast, phytoavailability of Cu (r = 0.41, p < 0.01) was only negatively related with soil DOC (dissolved organic carbon).

Effects of Organic Fertilizer on Cd Bioavailability and Cd Accumulation in Rice Grown in Contaminated Paddy Soil

The effects of organic fertilizer on Cd phytoavailability and distribution in rice plants(Oryza sativaL.) were examined in pot and field experiments. The results of the pot experiment show that the addition of organic fertilizer increased the oxidizable Cd fraction(F3) and decreased the soluble and exchangeable Cd fraction (F1). There was also an increase in the dry matter yield when more organic fertilizer was applied. The Cd concentrations in the rice plant parts were observed in the following order: root &gt; stem &gt; grain. The accumulation index from the field experiment indicates that organic fertilizer application is likely to reducethe uptake of both Cd and Zn by rice.

Biochar and Glomus caledonium influence Cd accumulation of upland kangkong (Ipomoea aquatica Forsk.) intercropped with Alfred stonecrop (Sedum alfredii Hance).

Both biochar application and mycorrhizal inoculation have been proposed to improve plant growth and alter bioaccumulation of toxic metals. A greenhouse pot trial was conducted to investigate growth and Cd accumulation of upland kangkong (Ipomoea aquatica Forsk.) intercropped with Alfred stonecrop (Sedum alfredii Hance) in a Cd-contaminated soil inoculated with Glomus caledonium and/or applied with biochar. Compared with the monocultural control, intercropping with stonecrop (IS) decreased kangkong Cd acquisition via rhizosphere competition, and also decreased kangkong yield. Gc inoculation (+M) accelerated growth and Cd acquisition of stonecrop, and hence resulted in further decreases in kangkong Cd acquisition. Regardless of IS and +M, biochar addition (+B) increased kangkong yield via elevating soil available P, and decreased soil Cd phytoavailability and kangkong Cd concentration via increasing soil pH. Compared with the control, the treatment of IS + M + B had a substantially higher kangkong yield (+25.5%) with a lower Cd concentration (−62.7%). Gc generated additive effects on soil alkalinization and Cd stabilization to biochar, causing lower DTPA-extractable (phytoavailable) Cd concentrations and post-harvest transfer risks.

Accumulation and Localization of Cadmium in Potato (Solanum tuberosum) Under Different Soil Cd Levels

Phytoavailability and uptake mechanism of Cd in edible plant tissues grown on metal polluted agricultural soils has become a growing concern worldwide. Uptake, transport, accumulation and localization of cadmium in potato organs under different soil Cd levels were investigated using inductively-coupled plasma mass spectrometry and energy dispersive X-ray microanalysis. Results indicated that Cd contents in potato organs increased with increasing soil Cd concentrations, and the order of Cd contents in different organs was leaves > stems/roots > tubers. Root-to-stem Cd translocation coefficients ranged from 0.89 to 1.81. Cd localization in potato tissues suggested that leaves and stems should be the main compartment of Cd storage and uptake. Although low concentrations of Cd migrated from the root to tuber, Cd accumulation in the tuber exceeded the standard for food security. Therefore, the planting of potato plants in farmland containing Cd should be closely evaluated due to its potential to present health risks.

Changes in Phytoavailability of Cadmium, Copper, Lead, and Zinc after Application with Eggshell in Contaminated Agricultural Soil

Agricultural soils surrounding mine areas in South Korea are often contaminated with multiple metals such as Cd, Pb and Zn. It poses potential risks to plants, soil organisms, groundwater, and eventually human health. The aim of this study was to examine the changes in phytoavailability of Cd, Cu, Pb and Zn after application with calcined eggshell (CES; 0, 1, 3, and 5% W/W) in an agricultural soil contaminated by mine tailings. The contents of Cd, Cu, Pb and Zn in soils were 8.79, 65.4, 1602, and <TEX>$692mgkg^{-1}$</TEX> (aqua regia dissolution), respectively. The experiments were conducted with lettuce (Lactuca sativa L. var. longifolia) grown under greenhouse conditions during a 30-d period. <TEX>$NH_4NO_3$</TEX> solution was used to examine the mobile fraction of these metals in soil. The application of CES dramatically increased soil pH and inorganic carbon content in soil due to CaO and <TEX>$CaCO_3$</TEX> of CES. The increased soil pH decreased the mobile fraction of Cd, Pb, Zn: from 3.49 to < <TEX>$0.01mgkg^{-1}$</TEX> for Cd, from 79.4 to <TEX>$1.75mgkg^{-1}$</TEX> for Pb, and from 29.6 to <TEX>$1.13mgkg^{-1}$</TEX> for Zn with increasing treatment of CES from 0 to 5%. In contrast, the mobile fraction of Cu was increased from 0.05 to <TEX>$3.08mgkg^{-1}$</TEX>, probably due to the formation of soluble <TEX>$CuCO_3{^0}$</TEX> and Cu-organic complex. This changes in the mobile fraction resulted in a diminished uptake of Cd, Pb and Zn by lettuce and an increased uptake of Cu: from 4.19 to < <TEX>$0.001mgkg^{-1}$</TEX> dry weight (DW) for Cd, from 0.78 to < <TEX>$0.001mgkg^{-1}$</TEX> DW for Pb, and from 133 to <TEX>$50.0mgkg^{-1}$</TEX> DW for Zn and conversely, from 3.79 up to <TEX>$8.21kg^{-1}$</TEX> DW for Cu. The increased contents of Cu in lettuce shoots did not exceed the toxic level of <TEX>$</TEX><TEX>></TEX><TEX>25mgkg^{-1}$</TEX> DW. The mobile contents of these metals in soils showed a strong relationship with their contents in plant roots and shoots. These results showed that CES effectively reduced the phytoavailability of Cd, Pb, and Zn to lettuce but elevated that of Cu in consequence of the changed binding forms of Cd, Cu, Pb, and Zn in soils. Based on these conclusions, CES can be used as an effective immobilization agent for Cd, Pb and Zn in contaminated soils. However, the CES should be applied in restricted doses due to too high increased pH in soils.

Saline irrigation and Zn amendment effect on Cd phytoavailability to Swiss chard (Beta vulgaris L.) grown on a long-term amended agricultural soil: a human risk assessment

Crops, particularly in the Northeast region of Mexico, have to cope with increasing soil salinization due to irrigation. Chloride (Cl(-)) concentration has been strongly related to enhance cadmium (Cd) uptake by plants due to increased solubility in the soil solution. The effect of irrigation with slightly saline water from a local well was evaluated in this work on the accumulation and translocation of Cd in Swiss chard (Beta vulgaris L.) grown in soil historically amended with stabilized sewage sludge under a regime of phosphorus and zinc fertilization. A factorial pot experiment was conducted with two phosphate fertilizer levels (PF, 0 and 80kgha(-1) dry soil, respectively), two Zn levels (0 and 7kgha(-1) dry soil), and two sources of water for irrigation deionized water (DW) and slightly saline well water (WW)from an agricultural site. Additionally, a human risk assessment for Cd ingestion from plants was assessed. Results showed that Cl(-) salinity in the WW effectively mobilized soil Cd and increased its phytoavailability. A higher level of Cd was found in roots (46.41mgkg(-1)) compared to shoots (10.75mgkg(-1)). Although the total content of Cd in the edible parts of the Swiss chard irrigated with WW exceeded permissible recommended consumption limit, bioavailable cadmium in the aboveground parts of the plant in relation to the total cadmium content was in the range from 8 to 32%. Therefore, human health risks might be overestimated when the total concentration is taken into account.

Cadmium phytoavailability to rice (Oryza sativa L.) grown in representative Chinese soils. A model to improve soil environmental quality guidelines for food safety

Food chain contamination by cadmium (Cd) is globally a serious health concern resulting in chronic abnormalities. Rice is a major staple food of the majority world population, therefore, it is imperative to understand the relationship between the bioavailability of Cd in soils and its accumulation in rice grain. Objectives of this study were to establish environment quality standards for seven different textured soils based on human dietary toxicity, total Cd content in soils and bioavailable portion of Cd in soil. Cadmium concentrations in polished rice grain were best related to total Cd content in Mollisols and Udic Ferrisols with threshold levels of 0.77 and 0.32mgkg−1, respectively. Contrastingly, Mehlich-3-extractable Cd thresholds were more suitable for Calcaric Regosols, Stagnic Anthrosols, Ustic Cambosols, Typic Haplustalfs and Periudic Argosols with thresholds values of 0.36, 0.22, 0.17, 0.08 and 0.03mgkg−1, respectively. Stepwise multiple regression analysis indicated that phytoavailability of Cd to rice grain was strongly correlated with Mehlich-3-extractable Cd and soil pH. The empirical model developed in this study explains the combined effects of soil properties and extractable soil Cd content on the phytoavailability of Cd to polished rice grain. This study indicates that accumulation of Cd in rice is influenced greatly by soil type, which should be considered in assessment of soil safety for Cd contamination in rice. This investigation concluded that the selection of proper soil type for food crop production can help us to avoid the toxicity of Cd in our daily diet.

Effectiveness of Phytoremediation Technologies to Clean Up of Metalloids Using Three Plant Species in Iran

Phytoremediation is a potential, innovative, and cost-effective technology for non-destructive remediation of heavy-metal contaminated soils. A field trial was conducted to evaluate the phytoremediation efficiencies of three plants and the effects of ethylenediaminetetraacetic acid (EDTA) or ammonium addition [(NH4)2SO4 and NH4NO3] for assisting removal of heavy metals (Pb, Hg, and Cd) from contaminated soil. The tested plants include Amaranthus retroflexus, Sorghum bicolor, and Lolium perrene. Results showed that maximum concentration of Pb, Hg, and Cd were detected in shoots of A. retroflexus, S. bicolor, and L. perrene at high concentrations in pH=6.2. The application of EDTA as a chelating agent to soil was the most efficient to enhance the phytoavailability of Pb, Hg and Cd. The concentrations of Pb, Hg, and Cd in the shoots of A. retroflexus treated with EDTA were 57 mg/kg, 14.1 mg/kg, and 30 mg/kg, respectively. Results indicated that among the three plants, A. retroflexus had great potential in phytoremediation of contaminated soils.

Effects of particle sizes of rock phosphate on immobilizing heavy metals in lead zinc mine soils

Abstract Phosphate-induced immobilization is recognized as one of effective in situ remediation methods for heavy metal contaminated soils. Phosphate-based minerals that adsorb, chelate, or complex heavy metals in soil were greatly concerned as effective heavy metals immobilizing materials. Effects of particle sizes of rock phosphate on immobilizing heavy metals in Pb-Zn mine soils by a greenhouse experiment was conducted. Rock phosphate was added to a Pb-Zn mine soil with four different particle sizes, D97<101.43 µm (UP), D97<71.12 µm (P1), D97<36.83 µm (P2) and D97< 4.26 µm (P3) (the diameters of 97% of the particles were less than 4.26 µm.), and 2 rates (2.5% and 5%). Lolium prenne , L. were grown in the treated soils. Compared to the control, addition of rock phosphate (RP) decreased metal contents in both roots and shoots significantly. Pb contents in shoots decreased by 19.59%-37.80% by different particle sizes at the rate of 5%, reaching lowest level at lowest particle size P3. Zn contents in shoots decreased by 13.47% -13.75 %, Cu in roots was decreased by 18.46%-67.98% and in shoots by 16.82%-32.61%, and Cd in roots decreased by 31.03%-74.23%. The results indicated that, RP can reduce the phytoavailability of Pb, Zn, Cu and Cd in soil significantly by immobilization and the effects strengthened with the decrease of particle size and increasing the rate of addition.

The impact of greenhouse vegetable farming duration and soil types on phytoavailability of heavy metals and their health risk in eastern China

Heavy metal contamination in vegetables from greenhouse vegetable production (GVP) in China requires major attention. For GVP sustainability at a large regional level, 441 surface GVP soil and 132 corresponding greenhouse vegetable samples were collected from six typical GVP bases in eastern China to systematically evaluate the impact of GVP duration and soil types (Anthrosols and Cambosols) on phytoavailability of four major metals, Cd, Cu, Zn, and Pb, and their health risk. The results revealed high Cd accumulation in leaf vegetables grown in Anthrosols, which might pose potential health risk. Regardless of soil types in the study region, greenhouse farming lowered soil pH and enhanced metal availability with rising GVP duration, which might exacerbate Cd phytoavailability and vegetable Cd contamination as well as potential health risk. Also, increased GVP soil organic matter contents over time, found in some locations, affected crop-depending Cu and Zn uptakes. Furthermore, due to GVP, the annual decrease rate of soil pH and increase rates of soil available metal concentrations were generally much greater in Anthrosols than those in Cambosols, which contributed a lot to high Cd uptake by leaf vegetables grown in Anthrosols and their potential health risk. From sustainable GVP perspective, fertilization strategy with reduced frequency and rate is especially important and effective for abating soil and vegetable contamination by heavy metals under greenhouse farming.

Effect of agro-industrial waste amendment on Cd uptake in Amaranthus caudatus grown under contaminated soil: An oxidative biomarker response

In the present study phytoavailability of Cd, growth yield, cellular Cd accumulation and oxidative stress responses were studied in leafy vegetable Amaranthus caudatus under soil amendments. The test plant was cultivated in Cd contaminated soil (6µgCdg−1 soil) amended with different doses: 0.5, 2, 5 and 10 percent of rice husk (RH), saw dust (SD), farmyard manure (FYM), farmyard in combination with nitrogen, and phosphorus and potassium (FYM+NPK). Phytoavailability of Cd in amended soil and cellular Cd accumulation in edible parts (shoot) of A. caudatus declined maximally with 5 percent dose of each amendment, and decrease in Cd content in tissues was 36, 45, 23 and 14 percent under FYM, FYM+NPK, RH and SD amendments, respectively, over the value recorded in plants grown in Cd contaminated non-amended soil (Cd+NA soil). The shoot yield in control plant cultivated in the absence of Cd without amendment (Cd−NA soil) was 18.1±0.98gfwplant−1 and it was declined up to 50 percent (9.2±0.80gfwplant−1) when plants were grown in Cd+NA soil. Amendments with 5 percent doses of FYM+NPK and FYM enhanced the yield up to 26.5±0.57 and 20.5±1.00gfwplant−1, respectively, which may be correlated with better mineral nutrients and organic carbon content in amended soil. RH and SD amendments with similar doses improved in yield up to 16.9±0.43 and 15.2±0.45gfwplant−1, respectively, however, it was still less than that of control. Further, correlation analysis of growth yield, Cd concentration and oxidative stress under these conditions suggest that with the decrease in cellular Cd concentration following amendment the level of oxidative markers (oxidants: O2− and H2O2 and lipid peroxidation: malondialdehyde; MDA) declined as a result of significant enhancement in the activity of enzymatic antioxidants (peroxidase, ascorbate peroxidase, superoxide dismutase, dyhydroascorbe reductase and catalase). Thus, the present technique can efficiently reduce the metal load in food chain and also increase plant yield, hence it could be applied in catchments area of urban cities where metal contamination has become an unavoidable factor.

Arbuscular mycorrhizal fungi enhance both absorption and stabilization of Cd by Alfred stonecrop (Sedum alfredii Hance) and perennial ryegrass (Lolium perenne L.) in a Cd-contaminated acidic soil

A greenhouse pot experiment was conducted to compare the phytoextraction efficiencies of Cd by hyper-accumulating Alfred stonecrop (Sedum alfredii Hance) and fast-growing perennial ryegrass (Lolium perenne L.) from a Cd-contaminated (1.6mgkg−1) acidic soil, and their responses to the inoculations of two arbuscular mycorrhizal (AM) fungal strains, Glomus caledonium 90036 (Gc) and Glomus mosseae M47V (Gm). Ryegrass and stonecrop were harvested after growing for 9 and 27 wk, respectively. Without AM fungal inoculation, the weekly Cd extraction by stonecrop (8.0μgpot−1) was 4.3 times higher than that by ryegrass (1.5μgpot−1). Both Gc and Gm significantly increased (P<0.05) root mycorrhizal colonization rates, soil acid phosphatase activities, and available P concentrations, and thereby plant P absorptions (except for Gm-inoculated ryegrass), shoot biomasses, and Cd absorptions (except for Gm-inoculated stonecrop), while only Gc-inoculated stonecrop significantly accelerated (P<0.05) the phytoextraction efficiency of Cd by 78%. In addition, both Gc and Gm significantly decreased (P<0.05) phytoavailable Cd concentrations by 21–38% via elevating soil pH. The results suggested the potential application of hyper-accumulating Alfred stonecrop associated with AM fungi (notably Gc) for both extraction and stabilization of Cd in the in situ treatment of Cd-contaminated acidic soil.

Root exudates from sunflower (Helianthus annuus L.) show a strong adsorption ability toward Cd(II)

Cd(II) adsorption of root exudates from sunflower (Helianthus annuus L.) seedling was investigated by Cd ion-selective electrode, Fourier Transform Infrared spectroscopy, and fluorescence spectroscopy. Root exudates from Helianthus annuus L. had strong adsorption ability toward Cd(II). The adsorption process was pH-dependent and the maximum adsorption capacity, 150.8 mg g−1, was observed at pH 7.0. Root exudates had pK a1 at 4.7 for carboxyl and pK a2 at 9.2 for phenolic, and amino groups. The aliphatic and aromatic (C−H) groups, amide III group, and the C (=O)−O and sulfonate groups were responsible for Cd(II) adsorption. The excitation emission matrix fluorescence spectroscopy showed protein-like substances participated in Cd adsorption and formed strong complexes, with conditional stability constants of 4.70 and 4.32, which is a little lower than that determined by potentiometric methods, 5.13. The strong Cd complexing ability of root exudates implies that root exudates may significantly affect mobility, toxicity, and phytoavailability of Cd. Cd binding of root exudates may be attributed to its interaction with the proteins, polysaccharides, and phenolic compounds in root exudates.

Cadmium uptake and subcellular distribution in rice plants as affected by phosphorus: Soil and hydroponic experiments

High cadmium (Cd) concentrations are a serious environmental problem in various agro-ecosystems and urban areas. Since mobile Cd in the soil can be accumulated in the food chain by plant uptake, remediation techniques to fix Cd in the soil in situ are urgently required, for which the application of phosphorus (P) is auspicious. The effects of P on soil pH, Cd phytoavailability, and Cd distribution with regard to rice plants were examined in a pot experiment using soil contaminated with 82 mg Cd kg -1 . A commercial P fertilizer (0-52-34, containing 52% P2O5 and 34% K2O) was applied to the soil to reach P concentrations of 0 (the control), 50, 200, and 1000 mg P kg -1 above the baseline P concentration of the soil. P-application increased the soil pH and caused a redistribution of Cd to less mobile fractions. Plant growth was also enhanced by P addition. Plant Cd uptake was only significantly reduced in mature plants receiving a P-application rate of 1000 mg P kg -1 . Additionally, a hydroponic experiment was carried out to study the effects of different P concentrations on the subcellular distribution of Cd in rice plants. When a P-application of 1000 mg L -1 was applied, the Cd proportions in the cell walls increased by 7% in the roots and 10% in the shoots, while reductions for the other fractions were observed, hinting at the occurrence of a detoxifying effect of P on the rice plant’s Cd concentration.