Showing papers on "Phytotoxicity published in 2003"

Immobilization and phytoavailability of cadmium in variable charge soils. II. Effect of lime addition

Abstract: The effect of pH-increases due to Ca(OH)2 and KOH addition on the adsorption of cadmium (Cd) was examined in two soils which varied in their variable-charge components. The effect of Ca(OH)2 on immobilization and phytoavailability of Cd from one of the soils, treated with various levels of Cd (0–10 mg Cd kg−1 soil), was further evaluated using mustard (Brassica juncea L.) plants. Cadmium immobilization in soil was evaluated by a chemical fractionation scheme. The addition of Ca(OH)2 and KOH increased the soil pH, thereby increasing the adsorption of Cd, the effect being more pronounced in the soil dominated by variable charge components. There was a greater increase in Cd2+ adsorption in the KOH-treated than the Ca(OH)2-treated soil, which is attributed to the greater competition of Ca2+ for adsorption. Increasing addition of Cd enhanced Cd concentration in plants, resulting in decreased plant growth (i.e., phytotoxicity). Although addition of Ca(OH)2 effectively reduced Cd phytotoxicity, Cd uptake increased at the highest level, probably due to decreased Cd2+ adsorption resulting from increased Ca2+ competition. There was a significant inverse relationship between dry matter yield and Cd concentration in soil solution. Addition of Ca(OH)2 decreased the concentration of the soluble + exchangeable Cd fraction but increased the concentration of inorganic-bound Cd fractions in soil. Since there was no direct evidence for CdCO3 or Cd(OH)2 precipitation in the variable charge soil used for the plant growth experiment, alleviation of phytotoxicity can be attributed primarily to immobilization of Cd by enhanced pH-induced increases in negative charge.

Effects of arsenate and phosphate on their accumulation by an arsenic-hyperaccumulator Pteris vittata L.

Abstract: Arsenate and phosphate interactions are important for better understanding their uptake and accumulation by plant due to their similarities in chemical behaviors. The present study examined the effects of arsenate and phosphate on plant biomass and uptake of arsenate and phosphate by Chinese brake (Pteris vittata L.), a newly-discovered arsenic hyperaccumulator. The plants were grown for 20 weeks in a soil, which received the combinations of 670, 2670, or 5340 μmol kg−1 arsenate and 800, 1600, or 3200 μmol kg−1 phosphate, respectively. Interactions between arsenate and phosphate influenced their availability in the soil, and thus plant growth and uptake of arsenate and phosphate. At low and medium arsenate levels (670 and 2670 μmol kg−1), phosphate had slight effects on arsenate uptake by and growth of Chinese brake. However, phosphate substantially increased plant biomass and arsenate accumulation by alleviating arsenate phytotoxicity at high arsenate levels (5340 μmol kg−1). Moderate doses of arsenate increased plant phosphate uptake, but decreased phosphate concentrations at high doses because of its phytotoxicity. Based on our results, the minimum P/As molar ratios should be at least 1.2 in soil solution or 1.0 in fern fronds for the growth of Chinese brake. Our findings suggest that phosphate application may be an important strategy for efficient use of Chinese brake to phytoremediate arsenic contaminated soils. Further study is needed on the mechanisms of interactive effects of arsenate and phosphate on Chinese brake in hydroponic systems.

Assessing lead thresholds for phytotoxicity and potential dietary toxicity in selected vegetable crops.

Abstract: Lead tolerance and accumulation in shoots and edible parts varied with crop species and soil type. The critical Pb concentrations at 10% yield reduction were 24.71, 28.25, and 0.567 mg kg−1 for pakchoi, celery, and hot pepper, respectively under hydroponic conditions, whereas were 13.1, 3.83, 0.734 mg kg−1 grown in the Inceptisol and 31.7, 30.0, 0.854 mg kg−1 in the Alluvial soil, respectively. Based on the threshold of human dietary toxicity for Pb, the critical levels of soil available Pb for pakchoi, celery, and hot pepper were 5.07, 8.06, and 0.48 mg kg−1 for the Inceptisol, and 1.38, 1.47, and 0.162 mg kg−1 for the Alluvial soil, respectively. Similarly, the total soil Pb thresholds were different from vegetable species and soil types.

Determining toxicity of lead and zinc runoff in soils: salinity effects on metal partitioning and on phytotoxicity.

Abstract: When assessingcationic metal toxicity in soils, metals are often added to soil as the chloride, nitrate, or sulfate salts. In many studies, the effects of these anions are ignored or discounted; rarely are appropriate controls included. This study used five soils varying in pH, clay content, and organic matter to determine whether salinity from counter-ions contributed to or confounded metal phytotoxicity. Varying rates of Pb and Zn were applied to soils with or without a leaching treatment to remove the metal counter-ion (NO3-). Lactuca sattva (lettuce) plants were grown in metal-treated soils, and plant dry weights were used to determine median effective concentrations where there was a 50% reduction in yield (EC50s) on the basis of total metals measured in the soil after harvest. In two of the five soils, leaching increased the EC50s significantly for Zn by 1.4- to 3.7-fold. In three of the five soils, leaching increased the EC50s significantly for Pb by 1.6- to 3.0-fold. The shift in EC50s was not a direct result of toxicity of the nitrate ion but was an indirect effect of the salinity increasing metal concentrations in soil solution and increasing its bioavailability for a given total metal concentration. In addition, calculation of potential salinity changes in toxicological studies from the addition of metals exhibiting strong sorption to soil suggested that if the anion associated with the metal is not leached from the soil, direct salinity responses could also lead to significant overestimation of the EC50 for those metals. These findings question the relevance of the application of single-metal salts to soils as a method of assessing metal phytotoxicity when, in many cases in our environment, Zn and Pb accumulate in soil over a period of time and the associated counter-ions are commonly removed from the soil during the accumulation process (e.g., roof and galvanized tower runoff).

A biotest for evaluating copper bioavailability to plants in a contaminated soil.

Abstract: This work aimed at defining the optimal conditions for a novel ecotoxicological test designed for evaluating the bioavailability and phytotoxicity of metals to plants. This biotest, which provided easy access to roots, shoots, and rhizosphere soil, was applied to a vineyard calcareous soil that had been contaminated by the application of Cu fungicides. A preliminary hydroponic experiment comparing various levels of solution Cu concentration enabled us to determine the no observable adverse effects concentration (NOAEC), which was in the range 5 to 20 microM total Cu (0.01-0.06 microM free Cu ion) for rape (Brassica napus L. cv. Goeland). For the biotest, rape was grown in hydroponic conditions for 21 d in pots designed so that plants developed a planar mat of roots at the surface of a polyamide mesh. By then, the plants were transferred for 4 or 8 d onto a 1- or 3-mm-thick soil layer that was separated from the root mat by the mesh and connected to a reservoir of nutrient solution or deionized water via a filter paper wick. An 8-d period was the best option as it enabled plant growth to be significant. The use of 1-mm soil thickness was recommended if the biotest aimed at investigating root-induced changes in the rhizosphere. Although it may cause some artifacts, compared with deionized water, nutrient solution provided better standardized conditions for comparing widely differing soil samples. The studied soil did not induce any Cu phytotoxicity in spite of its fairly large total Cu content.

Efficacy and phytotoxicity of lime sulphur in organic apple production

Abstract: Curative and preventive efficacy and phytotoxicity of lime sulphur spray schedules, based on a warning system, were evaluated in the Netherlands during two growing seasons under field conditions. In most cases, lime sulphur treatments applied either curatively or preventively resulted in significantly lower scab damage on both the leaves and fruits compared to wettable sulphur treatments. However, all lime sulphur treatments showed high phytotoxicity values, reduced leaf size and had a tendency to a reduced yield quality compared to all other treatments. For curative schedules of lime sulphur on scab control, phytotoxicity and yield did not differ significantly from preventive schedules of lime sulphur. However, the use of a warning system combined with curative schedules of lime sulphur saved one and two lime sulphur sprays in 2000 and 2001, respectively, compared to the preventive treatments of lime sulphur. Our results demonstrated that a curative spray programme with lime sulphur at 0.75-2%, applied 35-45 h after predicted infection periods, can provide effective primary apple scab control, but no benefit in either yield or fruit quality was reached under organic growing conditions. Moreover, research herein clearly showed that organic growers are forced to find a balance between good efficacy and phytotoxic effects of lime sulphur.

Does aluminium phytotoxicity induce oxidative stress in greengram (vigna radiata)

Abstract: Summary. To verify whether aluminium phytotoxicity causes oxidative stress in developing greengram seedlings, the present investigation was carried out. An uniform decrease in root and shoot elongations was marked as the primary signs of aluminium injury. A significant increase in lipid peroxidation measured in terms of TBARS content was noticed which was also correlated with an increase in membrane injury index. The increase in peroxide content was accompanied by a decrease in catalase (CAT, EC 1.11.1.6) activity. However, superoxide dismutase (SOD, EC 1.15.1.9), peroxidase (POX, EC 1.11.1.6) and glutathione reductase (GR, EC 1.6.4.2) activities increased with increasing aluminium concentrations. Both glutathione and ascorbate contents showed a decrease at a higher metal concentration. These results suggested an induction of oxidative stress in developing greengram seedlings under aluminium phytotoxicity.

Correlation between phytotoxicity on annual ryegrass (Lolium rigidum) and production dynamics of allelochemicals within root exudates of an allelopathic wheat

Abstract: An improved allelopathic correlation between phytotoxicity measured in root growth bioassay upon annual ryegrass (Lolium rigidum Gaud.) and the concentrations of a selection of dynamically produced allelochemicals quantified in the root exudates of cv. Khapli wheat (Triticum turgidum ssp. durum (Desf.) Husn.) monitored during the first 15 days of wheat seedling growth in a sterile, agar-water medium, has been established. Changes over the 15-day growth period in the quantities of five exuded benzoxazinones and seven phenolic acids were measured simultaneously using GC/MS/MS. Substantiating pure compound dose-response measurements were conducted over a range of concentrations for the putative allelochemicals within the wheat exudates. One synergism-based proposal using the monitored compounds to explain the observed low-exudate-concentration phytotoxicity was explored, but was found to be experimentally inadequate.

Identification and quantitation of allelochemicals from the lichen Lethariella canariensis: phytotoxicity and antioxidative activity.

Abstract: Phytotoxicity-based extraction and fractionation were employed to separate allelochemicals contained in an extract of Lethariella canariensis. Twelve phenolic substances were isolated from the phytotoxic fraction "Letharal" of the thalli. These were identified by spectroscopic methods, physicochemical constants, and HPLC chemical correlation, and determined to be atranol (2), chloroatranol (3), hematommic acid (4), chlorohematommic acid (5), methyl hematommate (6), methyl chlorohematommate (7) (new compound), ethyl hematommate (8), ethyl chlorohematommate (9), methyl beta-orsellinate (10), atranorin (11), chloroatranorin (12), and (+)-usnic acid (13). Further identification and quantification of these allelochemicals in the environment were conducted by HPLC. Several phenolic compounds showed moderate antimicrobial activity. The cytostatic activity of the polyphenols was investigated on U937 and HL-60 cells. All compounds were assayed, with the exception of 10. The "Letharal" mixture decreased cell viability in both cell lines. Protection against lipid peroxidation was investigated using brain homogenates. Compounds 2, 3, 6, 8, 11, and Letharal decreased H2O2/Fe+2 induced lipid peroxidation in a concentration-dependent manner, while 10 and 13 were unable to protect tissue against oxidative stress.

Phytotoxic Interference of Ageratum conyzoides with Wheat (Triticum aestivum)

Abstract: A study was conducted to assess the phytotoxicity of Ageratum conyzoides, a weed of cultivated areas, to the growth and establishment of wheat (Triticum aestivum). The lengths of the radicle and coleoptile and the seedling dry weight of wheat were significantly reduced when wheat was grown in field soil previously infested with A. conyzoides, compared to control soil collected from an area devoid of this weed. Even extracts prepared from A. conyzoides soil were inhibitory, indicating the presence of some water-soluble phytotoxins in the soil. To determine the possible contribution of the weed in releasing these phytotoxins, growth studies involving leaf residues and their extracts and amended soils (prepared by incorporating leaf residues and residue extracts) were also performed on wheat. With all treatments, an inhibitory effect of A. conyzoides was found, compared to respective controls. A significant amount of water-soluble phytotoxins (the phenolics) was found to be present in the soil infested with A. conyzoides, leaf residues and the amended soils. The amount of phenolics correlated well with growth performance in the respective treatments. This study establishes the phytotoxicity of leaf residues of A. conyzoides to wheat through the release of phenolics into the soil, which may serve as possible tools in establishing its allelopathy.

Role of Organic Matter in Alleviating Soil Acidity

Abstract: The principal adverse effects of acidity on soil fertility occur at soil pH values below 5.5 due to acid dissolution of aluminum (Al) and the onset of Al phytotoxicity to susceptible plants [1]. Aluminum phytotoxicity results in rapid inhibition of root growth due to impedance of both cell division and elongation [1]. This results in reduced volume of soil explored by the root system and direct interference with uptake of ions such as calcium and phosphate across the cell membrane of damaged roots [2]. These phytotoxic effects are unimportant in moderately acidic soils with pH values of 5.5 to 6.5 when the concentration of toxic forms of Al is normally negligible. Manganese toxicity and deficiencies of phosphorus, calcium, and magnesium are common in acidic soils. Soil nutrient deficiencies exacerbate the problem of inefficient nutrient uptake due to restricted root growth and root damage [3]. In drier environments, poor water use due to poor root development is considered to be another adverse effect of Al phytotoxicity.

Phytotoxicity of aluminium to wheat plants in high-pH solutions

Abstract: Phytotoxicity of aluminium in acid soils is well known. At pH ≥6.3, aluminate [Al(OH)4–] is the principal hydroxo-aluminium species in soil solutions; however, its phytotoxicity has not received much attention. Sodic subsoils in Australia are generally alkaline and have pH above 9. During our survey of 8 subsoils in South Australia, we found aluminate ions at concentrations greater than 0.8 mg/L (29.7 μmol/L of aluminium) in soil solutions when pH was greater than 9, with corresponding high uptake of aluminium by wheat plants. We studied the phytotoxicity of aluminium to wheat plants in solution culture by maintaining the pH of alkaline solutions at 9.2. Relative root lengths of wheat plants, compared with those in reverse-osmosis deionised water, were significantly reduced in alkaline solutions and CO2-free air indicated toxicity of hydroxy, carbonate and bicarbonate ions. Further reduction of root lengths due to aluminate toxicity was also evident. Relative root lengths of wheat plants, when comparing between +aluminium and –aluminium treatments, were reduced up to 50% in alkaline solutions containing as low as 1 mg/L of aluminium. Aluminium accumulated mainly in the roots, thereby reducing their growth. In bicarbonate solutions, aluminium toxicity under alkaline pH was highly significant (P<0.001). However, at the same level of added aluminium in carbonate solutions, relative root length was not reduced. This study concludes that when aluminium species are present at a concentration of about 1 mg/L in soil solutions with pH greater than 9, the growth of wheat plants could be significantly affected.

Upland Rice and Allelopathy

Abstract: Upland rice (Oryza sativa L.) is mainly grown in Asia, Africa and Latin America. Yield potential of upland rice is quite low and invariably this crop is subjected to many environmental stresses. Further, when upland rice is grown in monoculture for more than two to three years on the same land, allelopathy or autotoxicity is frequently reported. Allelopathy involves complex plant and plant chemical interactions. The level of phytotoxicity of allelochemicals is influenced by abiotic and biotic soil factors. Adopting suitable management strategies in crop rotation can reduce or eliminate allelochemicals phytotoxicity. Rice yields can be improved by growing rice in rotation with other crop species. Allelochemicals of rice can be used for control of weeds in this crop as well as other crops that are grown in rotation with rice. This review highlights that present knowledge of allelopathy in upland rice is inadequate and fragmentary, and therefore, more controlled and field studies are needed to understand and...

Allelopathic Potential of Macaranga tanarius (L.) Muell.–Arg.

Abstract: Macaranga tanarius is widely distributed in the abandoned lowlands of Taiwan where substantial amounts of leaves accumulate on the ground. A unique pattern of weed exclusion underneath trees is often found and thought to result from allelopathic interactions. Density-dependent phytotoxicity analysis of Lactuca sativa L. (lettuce) growing in soil mixed with the powder of M. tanarius leaves showed a significant deviation from the expected yield–density relationship. Lettuce growth was most suppressed in the low seed density experiment suggesting that the phytotoxins produced during leaf decomposition inhibit the growth of lettuce seedlings. Bidens pilosa and Leucaena leucocephala, growing in soil mixed with the leaf powder of M. tanarius were also suppressed. Aqueous leaf extracts were bioassayed against lettuce and B. pilosa, and exhibited a significant suppression in radicle growth. Compounds identified from leaves included nymphaeol-A (1), nymphaeol-B (2), nymphaeol-C (3), quercetin (4), abscisic acid (ABA) (5), blumenol A (6), blumenol B (7), roseoside II (8), tanariflavanone A (9), and tanariflavanone B (10). ABA was the major growth inhibitor. At concentrations of 20 ppm, ABA suppressed lettuce germination, while at 120 ppm it inhibited the growth of Miscanthus floridulus, Chloris barbata, and Bidens pilosa. At 600 ppm, quercetin, blumenol A, and blumenol B, caused 20–25% inhibition of radicle and shoot growth of M. floridulus. The amount of ABA in M. tanarius leaves was approximately 3–5 μg g−1 dry weight, significantly higher than previously reported. We conclude that the pattern of weed exclusion underneath stands of M. tanarius and its invasion into its adjacent grassland vegetation results from allelopathic interactions.

Optimizing phytoremediation of heavy metal-contaminated soil by exploiting plants' stress adaptation.

Abstract: Soil phytoextraction is based on the ability of plants to extract contaminants from the soil. For less bioavailable metals, such as Pb, a chelator is added to the soil to mobilize the metal. The effect can be significant and in certain species, heavy metal accumulation can rapidly increase 10-fold. Accumulation of high levels of toxic metals may result in irreversible damage to the plant. Monitoring and controlling the phytotoxicity caused by EDTA-induced metal accumulation is crucial to optimize the remedial process, i.e. to achieve maximum uptake. We describe an EDTA-application procedure that minimizes phytotoxicity by increasing plant tolerance and allows phytoextraction of elevated levels of Pb and Cd. Brassica juncea is tested in soil with typical Pb and Cd concentrations of 500 mg kg-1 and 15 mg kg-1, respectively. Instead of a single dose treatment, the chelator is applied in multiple doses, that is, in several small increments, thus providing time for plants to initiate their adaptation mechanisms and raise their damage threshold. In situ monitoring of plant stress conditions by chlorophyll fluorescence recording allows for the identification of the saturating heavy metal accumulation process and of simultaneous plant deterioration.

Phytotoxicity of the tetramic acid metabolite trichoetin

Abstract: Trichosetin, a tetramic acid-containing metabolite produced in the dual culture of Trichoderma harzianum and Catharanthus roseus (L.) G. Don callus, was subjected to phytotoxicity assays. In seedling growth assays, trichosetin inhibited root and shoot growth of all five plant species tested by damaging the cell membrane, as evidenced by the dose-dependent increase in electrolyte leakage and lipid peroxidation. Vital staining of trichosetin-treated Nicotiana tabacum BY-2 cells, with rhodamine 123, showed a weaker green fluorescence compared to controls indicating damaging effects on mitochondria. FDA-PI staining, to determine cell viability, indicated that cells of the trichosetin-treated roots were mostly dead.

Allelochemical potential of Callicarpa acuminata.

Abstract: The allelochemical potential of Callicarpa acuminata (Verbenaceae) was investigated by using a biodirected fractionation study as part of a long-term project to search for bioactive compounds among the rich biodiversity of plant communities in the Ecological Reserve El Eden, Quintana Roo, Mexico. Aqueous leachate, chloroform-methanol extract, and chromatographic fractions of the leaves of C. acuminata inhibited the root growth of test plants (23–70%). Some of these treatments caused a moderate inhibition of the radial growth of two phytopathogenic fungi, Helminthosporium longirostratum and Alternaria solani (18–31%). The chloroform-methanol (1:1) extract prepared from the leaves rendered five compounds: isopimaric acid (1), a mixture of two diterpenols [sandaracopimaradien-19-ol (3) and akhdarenol (4)], α-amyrin (5), and the flavone salvigenin (6)]. The phytotoxicity exhibited by several fractions and the full extract almost disappeared when pure compounds were evaluated on the test plants, suggesting a synergistic or additive effect. Compounds (4), (5), and the semisynthetic derivative isopimaric acid methyl ether (2) had antifeedant effects on Leptinotarsa decemlineata. Compound 5 was most toxic to this insect, followed by (2), (4), and (6) with moderate to low toxicity. No correlation was found between antifeedant and toxic effects on this insect, suggesting that different modes of action were involved. All the test compounds were cytotoxic to insect Sf9 cells while (6), (4), and (1) also affected mammalian Chinese Hamster Ovary (CHO) cells. Compound 5 showed the strongest selectivity against insect cells. This study contributes to the knowledge of the defensive chemistry and added value of C. acuminata.

Phytotoxic effects of wheat extracts on a herbicide-resistant biotype of annual ryegrass (Lolium rigidum).

Abstract: Thirty-nine wheat accessions were used to evaluate their extract phytotoxicity against annual ryegrass (Lolium rigidum Gaud) Aqueous extracts of wheat shoot residues significantly inhibited the germination and root growth of a biotype of annual ryegrass resistant to herbicides of acetyl CoA carboxylase inhibitors (group A), acetolactate synthase inhibitors (B), photosystem II inhibitors (C), and tubulin formation inhibitors (D) The germination of the herbicide resistant (HR) biotype was inhibited by 3-100%, depending upon the wheat accession The phytotoxic effects on ryegrass root growth ranged from 12% stimulation to 100% inhibition, compared to a control The germination and root growth of a herbicide-susceptible (HS) biotype of annual ryegrass were also inhibited by the wheat extracts, with germination inhibited by 4-100%, and root growth by 19-100% Bioassays with two known wheat allelochemicals showed that p-coumaric acid and propionic acid significantly inhibited the growth of both HR and HS biotypes of annual ryegrass The two compounds completely inhibited the root growth of HR ryegrass at concentrations greater than 50 mM In comparison with p-coumaric acid, propionic acid was more inhibitory to seed germination, shoot, and root growth of both ryegrass biotypes The root growth of the HR biotype was more sensitive when exposed to wheat extracts, to p-coumaric acid, and to propionic acid The results suggest that residues of certain wheat cultivars with strong allelopathic potential could provide a nonherbicidal alternative for the management of herbicide-resistant weed species

Two isoflavones and bioactivity spectrum of the crude extracts of Iris germanica rhizomes

Abstract: In vitro biological activities including bactericidal, fungicidal and insecticidal activities as well as phytotoxicity and brine shrimp toxicity of the petroleum ether, chloroform and ethyl acetate extracts of Iris germanica L. were determined. The bactericidal activity of the extracts was assayed by the agar well diffusion test. In the fungicidal test, the agar tube dilution method was used. The insecticidal activity was determined by the exposure method. The toxicity of the extracts was evaluated by the phytotoxicity test as well as the brine shrimp toxicity test. The chloroform and ethyl acetate extracts of I. germanica rhizomes exhibited bactericidal activity, while the petroleum ether extract did not exhibit any bactericidal, fungicidal and insecticidal activities. It was also inactive in the brine shrimp toxicity test, whereas it showed significant phytotoxicity against the plant Lemna aequinoctialis Welv. Two known isoflavones were isolated from the chloroform extract of the plant.

Seleção de plantas com potencial para fitorremediação de tebuthiuron

Abstract: This study aimed to select tebuthiuron- tolerant plants to use them in phytoremediation programs in contaminated soils. The evaluated species were: Amaranthus hybridus, Crotalaria juncea, C. hyssopifolia, Chamaesyce hirta, Canavalia ensiformes, Helianthus annus, Pennisetum typhoides, Estizolobium aterrimum, Raphanus raphanistrum and Crotalaria incana. The experiment was carried out in a greenhouse, with a sandy-clay soil with 2.18 dag kg-1 of organic matter, in pots of 3 dm3 capacity. The experiment was arranged in a 10 x 4 x 4 factorial scheme in a randomized block design with three replications. The treatments consisted of: 10 species, four tebuthiuron doses (0.0; 0.5; 1.0 e 2.0 kg ha-1) applied in pre-emergence, and four evaluation times (15, 30, 45, and 60 days after sowing). Phytotoxicity, plant height and, above-ground, root and total biomass dry matter were evaluated. Canavalia ensiformes and Pennisetum typhoides were tolerant to tebuthiuron at the dose of 0.5 kg ha-1, and Estizolobium aterrimum up to the dose of 1.0 kg ha-1, with the latter showing less phytotoxicity symptoms and a smaller reduction of plant height, above-ground, root, and total biomass dry matter, as compared to the control treatment.

Zinc phytotoxicity to oilseed rape grown on zinc-loaded substrates consisting of Fe oxide-coated and calcite sand

Abstract: The risk of zinc (Zn) phytotoxicity in soils has increased in various regions following application of different anthropogenic materials. In order to assess the relative efficiency of Fe oxide and calcite in sorbing Zn and hence alleviating Zn phytotoxicity, we grew oilseed rape for 28 days in pots containing Zn-loaded model substrates consisting of Fe oxide (ferrihydrite)-coated sand (FOCS, 0.2–0.5 mm, 0.3 m2 ferrihydrite g−1 sand) and calcium carbonate (calcite) sand (CCS, 0.2–0.5 mm, 0.3 m2 calcite g−1 sand). Five substrates containing 5, 10, 20, 40, and 80% FOCS and supplied with ZnSO4 at a rate of 30, 100, 300, and 1000 mg Zn kg−1 were used in the cropping experiment and in an in vitro study of Zn desorption for 62 days. Plants exhibited good growth and a similar dry matter yield (DMY) at the 30 and 100 mg Zn kg−1 rates. On the other hand, DMY was markedly reduced at the 300 and, especially, at the 1000 mg Zn kg−1 rate, particularly for the substrates with the higher FOCS proportions. Symptoms of phytotoxicity (viz. chlorosis, purple colouration due to P deficiency) were apparent at such rates and were accompanied by high Zn concentrations in both shoot (average values >1000 and >1500 mg Zn kg−1 dry matter for the 300 and 1000 mg Zn kg−1 rate, respectively) and root (average values >2500 and >6000 mg Zn kg−1 dry matter for the 300 and 1000 mg Zn kg−1 rate, respectively). Total Zn uptake was maximal at 300 mg Zn kg−1. The results of water extractable Zn in the substrate after cropping and the dissolved Zn concentrations measured in substrate–water systems (desorption experiment) suggest that, on a surface area basis, calcite is more effective than Fe oxide to retain Zn and thus alleviate phytotoxicity at high Zn loadings. However, the Zn-sorption capacity of the Fe oxide cannot be neglected, particularly at low Zn loadings, where Fe oxide seems to exhibit a higher affinity for Zn – but not a higher Zn-sorption capacity – than does calcite.