Riparian Shrub Metal Concentrations and Growth in Amended Fluvial Mine Tailings

Fluvial mine tailing deposition has caused extensive riparian damage throughout the western USA. Willows are often used for fluvial mine tailing revegetation, but some accumulate excessive metal concentrations potentially detrimental to browsers. This greenhouse experiment evaluated growth and metal accumulation of Geyer willow (Salix geyeriana Andersson), Drummond’s willow (Salix drummondiana Barratt ex Hook.), diamondleaf willow (Salix planifolia Pursh), Bebb willow (Salix bebbiana Sarg.), thinleaf alder [Alnus incana (L.) Moench spp. tenuifolia (Nutt.) Breitung], water birch (Betula occidentalis Hook.), red-osier dogwood (Cornus sericea L. spp. sericea), and shrubby cinquefoil [(Dasiphora fruticosa (L.) Rydb. ssp. floribunda (Pursh) Kartesz)]. Bare-root shrubs were grown in tailings collected from three acidic, metal-contaminated (i.e., Cd, Cu, Pb, and Zn) fluvial deposits near Leadville, Colorado, USA. Tailings were amended with only lime to raise the soil pH to 7 s.u., or with lime and composted biosolids (224 Mg ha⁻¹). All shrubs survived in the amended tailings; composted biosolids had little effect on plant biomass. Aboveground and belowground biomass increased during the 2-month greenhouse study by 3–9 and 1.5–5 times initial values, respectively. Most shrubs accumulated Pb and Cu in roots, and belowground Pb concentrations in all shrubs were significantly reduced by the addition of composted biosolids. Compared to other species, alder and cinquefoil accumulated Pb in aboveground growth, and concentrations exceeded animal toxicity thresholds, but these shrubs normally comprise a small proportion of animal diets. Dogwood, alder, and cinquefoil contained low Cd concentrations in aboveground new growth, whereas Bebb and Geyer willow contained zootoxic concentrations. Dogwood, alder, and cinquefoil are three good candidates for mine tailing revegetation, especially in fluvial deposits with elevated Cd concentrations.     

铅锌矿废弃地尾矿砂对银合欢幼苗定居的影响

研究了广东省仁化县韶关凡口铅锌矿废弃地尾矿砂对银合欢(Leucaena glauca)幼苗定居的影响。结果表明，尾矿砂中Pb、Zn、Cu、Cd等重金属含量极高，Pb、Zn比对照土壤高100倍左右，Cu、Cd高4～5倍，植物对重金属的吸收、积累量较大，且多集中于根部。尾矿砂中硝态氮(NO^-₃-N)和铵态氮(NH⁺₄-N)含量很低，仅为对照土壤的13%～23%。银合欢幼苗在尾矿砂中能生长，但其叶片光合色素含量较少，株高、复叶数、植株干物质量等生物量显著降低，这主要是由于重金属含量过高导致根系活力降低，限制了植物对水分和营养物质的吸收，其次是土壤贫瘠的影响。     

Using native plants to evaluate the effect of arbuscular mycorrhizal fungi on revegetation of iron tailings in grasslands

A pot experiment was conducted to evaluate native plant species associated with exogenous AMF for their suitability in the revegetation of iron mine tailings of Inner Mongolia grassland. Agropyron cristatum (L.) Gaertn. and Elymus dahuricus Turcz. associated with AMF, Glomus mosseae, or Glomus versiforme, were grown on iron mine tailings to assess the mycorrhizal effects on plant growth, mineral nutrition uptake, C:N:P stoichiometry, and heavy metals uptake. The symbiotic associations were successfully established between exogenous AMF and two native plants, and root colonization rates of G. versiforme were significantly (P?<?0.05) higher than those of G. mosseae. G. versiforme was more effective than G. mosseae in promoting plant growth by significantly (P?<?0.05) increasing the concentrations of N, P, and K and decreasing the ratios of C:N:P. The shoot and root dry weights of A. cristatum and E. dahuricus were increased by 51–103 %. The N, P, and K concentrations of shoots and roots of two plants were increased by 18–236 %. Inoculation with AMF also significantly (P?<?0.05) decreased concentrations of heavy metals in the shoots and increased those in the roots, indicating that AMF could confer some degree of heavy metal tolerance to plants. The results indicated that plant inoculation with G. versiforme was more suitable than inoculation with G. mosseae for the revegetation of iron mine tailings. The experiment provided evidence for the potential use of local plant species in combination with exogenous AMF for ecological restoration of metalliferous tailings in arid and semi-arid grassland.     

Does returning sites of historic peri‐urban waste disposal to vegetable production pose a risk to human health? – A case study near Manchester,UK

Urban waste disposal occurred on fenland to the west of Manchester, England, between 1900 and 1964. The reclaimed fenland, Chat Moss, is now used for mixed arable farming. A total of 1.92 Mt of waste including privy midden, street sweepings, clinkers and slaughterhouse refuse was incorporated into the moss resulting in a modified topsoil with raised pH and reduced organic matter content compared with the subsoil. Elevated levels of potentially toxic elements (PTEs) are observed in the topsoil beyond the typical depth of atmospheric contamination; Cd and As concentrations exceed soil guideline values (SGVs) at 1.8 and 43 mg/kg, respectively. Sequential extraction indicates that waste‐derived Pb, Zn and Ni remain predominantly in the residual fraction, whereas Cu was mainly organically bound. Arsenic was predominately found in oxide and organic matter fractions with Cd in carbonate, oxide, organic matter and residual fractions. Pot trials indicated limited uptake of PTEs by vegetables grown on the waste‐amended soil, with the exception of Cd uptake by lettuce (0.22 mg/kg FW) and Pb uptake by radish (0.16 mg/kg FW), which exceeded current EU limits of 0.2 and 0.1 mg/kg FW, respectively. Hazard quotients (HQs) identified no risks to adults from consumption of vegetables grown in these soils with the exception of lettuce consumption with a HQ of 1.4. Risks to children were slightly greater with HQs >1 for Cd in lettuce, spinach, carrots and onion, As in lettuce, parsley and onion and for Zn in spinach.     

Revegetation of copper mine tailings with ryegrass and willow

To restore vegetation on metal mine tailings is very difficult because they often contain high concentrations of heavy metals, low nutrient content and low water retention capacity. This study involved 3 experiments that evaluated the effects of 4 treatment amendments: montmorillonite, rice straw, organic manure and chemical fertilizer on the growth of ryegrass (Loliurn perenne L.) and willow (Salix virninalis L.) with Cu and Zn mine tailings from two mining areas. The results showed that ryegrass was the most tolerant of 4 crops to Cu toxicity. Also when organic manure, which contained high concentrations of inorganic salts, was added to the mine tailings, it significantly hindered ryegrass growth (P=0.05).Meanwhile, with ryegrass organic manure significantly increased (P=0.05) the extractable Cu concentration in both mine tallings. When montmorillonite was used as a mine tailings amendment with willow, the height and tress number at the 1st cut were significantly greater (P = 0.05) than a control without montmorillonite. However there was no significant difference for height, tress number, dry weight or root dry weight at the 2nd cut. So, amendment applications to reduce metal toxicity and increase nutrients retention in mine tailings were essential during revegetation of mine tailings.     

Evaluation of the rehabilitation procedure of a pyritic mine tailings pond in Avoca,Southeast Ireland

A 32 ha tailings pond used for the disposal of pyritic mine waste was examined after a period of eight years to determine the success of the rehabilitation plan used to revegetate the site. This was achieved by examining both the vegetation cover and the quality of the topsoil in order to determine the effect of the tailings. A number of floristic habitats were identified within the site indicating that succession had occurred since revegetation of the area with metal-tolerant grass species. Four main habitats were investigated: leguminous, grass, gorse and low canopy. The soil layer in Shelton Abbey was 25–30 cm deep and contained levels of nutrients and metals comparable to those found in unpolluted soils. It was followed by a 20–25 cm layer of mixed soil and tailings, followed by the tailings only. The tailings retained elevated concentrations of metals indicating their unsuitability for growth of unadapted plant species. Vegetation from all habitats, analysed both in the summer and winter, contained higher levels of iron only compared with vegetation grown on unpolluted soils. Metals do not appear to be significantly leached from the tailings either into the soil or into surface and ground waters, and have not been accumulated to above normal levels by plant uptake. The rehabilitation protocol used at the site appears to have been successful. However, the site needs to be managed on an on-going basis to ensure the integrity of the bund and revegetated area. © 1998 John Wiley & Sons, Ltd.     

Quantitative Assessment of Effects of Cadmium on the Histological Structure of Poplar and Willow Leaves

Stem cuttings with homogenous diameter of Populus x euramericana (clone I-214) and Salix fragilis L. were grown in growth chamber in water culture method. After 45?days, the plants were treated with 10^?7 and 10^?5?M cadmium (Cd). As these species have different phytoextraction potentials, there is a need to analyze the level of Cd uptake, its translocation into aboveground organs, and changes in leaf structure. We analyzed micromorphological leaf characteristics: a fresh mass of the root, stem, and leaf, as well as a Cd concentration within them. Besides, we compared 23 micromorphological leaf blade quantitative traits of poplar and willow and monitored the structural changes induced by the intoxication of stem cuttings. Percent of Cd accumulation and translocation in plant organs varied between species. It depended on the level of Cd applied. When compared to the poplar clone, S. fragilis had a smaller leaf area and epidermal cells, thicker palisade tissue, smaller lumen of main vein vessels, and a higher percentage of main vein xylem. S. fragilis had more distinctive xeromorphic characteristics in the lamina structure. Increased concentrations of Cd led to significant structural changes, mainly in the main vein. When searching for valid parameters in assessing plant to be utilized in phytoremediation, it is necessary to take into consideration the interrelation of a large number of micromorphological parameters together with physiological and biochemical characteristics.     

Arbuscular mycorrhizal fungi regulate plant mineral nutrient uptake and partitioning in iron ore tailings undergoing eco-engineered pedogenesis

Excess available K and Fe in Fe ore tailings with organic matter amendment and water-deficiencies may restrain plant colonization and growth, which hinders the formation of eco-engineered soil from these tailings for sustainable and cost-effective mine site rehabilitation. Arbuscular mycorrhizal (AM) fungi are widely demonstrated to assist plant growth under various unfavorable environments. However, it is still unclear whether AM symbiosis in tailings amended with different types of plant biomass and under different water conditions could overcome the surplus K and Fe stress for plants in Fe ore tailings, and if so, by what mechanisms. Here, host plants (Sorghum sp. Hybrid cv. Silk), either colonized or noncolonized by the AM fungi (Glomus spp.), were cultivated in lucerne hay (LH, C:N ratio of 18)- or sugarcane mulch (SM, C:N ratio of 78)-amended Fe ore tailings under well-watered (55% water-holding capacity (WHC) of tailings) or water-deficient (30% WHC of tailings) conditions. Root mycorrhizal colonization, plant growth, and mineral elemental uptake and partitioning were examined. Results indicated that AM fungal colonization improved plant growth in tailings amended with plant biomass under water-deficient conditions. Arbuscular mycorrhizal fungal colonization enhanced plant mineral element uptake, especially P, both in the LH- and SM-amended tailings regardless of water condition. Additionally, AM symbiosis development restrained the translocation of excess elements (i.e., K and Fe) from plant roots to shoots, thereby relieving their phytotoxicity. The AM fungal roles in P uptake and excess elemental partitioning were greater in LH-amended tailings than in SM-amended tailings. Water deficiency weakened AM fungal colonization and functions in terms of mineral element uptake and partitioning. These findings highlighted the vital role AM fungi played in regulating plant growth and nutrition status in Fe ore tailings technosol, providing an important basis for involvement of AM fungi in the eco-engineered pedogenesis of Fe ore tailings.     

Effects of arbuscular mycorrhizal fungi on maize (Zea mays L.) and sorghum (Sorghum bicolor L. Moench) grown in rare earth elements of mine tailings

Rare earth elements (REE) of mine tailings have caused various ecological and environmental problems. Revegetation is one of the most cost-effective ways to overcome these problems, but it is difficult for plants to survive in polluted tailings. Arbuscular mycorrhizal fungi (AMF) can provide biotic and abiotic stress tolerance to its host plant and has widely adopted for the revegetation of degraded ecosystems. However, little is known about whether AMF plays role in facilitating the revegetation of REE of mine tailings. The objective was to investigate the uptake of nutrients and REE when plants are inoculated with AMF. A greenhouse pot experiment was conducted on the effects of Glomus mosseae and Glomus versiforme for the growth, nutritional status, and uptake of REE and heavy metals by maize (Zea mays L.) or sorghum (Sorghum bicolor L. Moench) grown in REE of mine tailings. The results indicated that symbiotic associations were successfully established between AMF and the two plant species. G. versiforme was more effective than G. mosseae at promoting plant growth by significantly increasing the uptake of nitrogen (N), phosphorus (P), and potassium (K) and decreasing carbon:nitrogen:phosphorus (C:N:P) stoichiometry. The shoot and root dry weights of the two plant species were increased by 211–387% with G. versiforme inoculation. Maize and sorghum exhibited significant differences in the REE concentrations in response to the colonization by AMF. The shoot and root lanthanum (La), cerium (Ce), praseodymium (Pr), and neodymium (Nd) concentrations of the maize inoculated with G. versiforme were decreased by approximately 70%, whereas those in the roots of sorghum were increased by approximately 70%. G. mosseae only significantly decreased the La, Ce, Pr, and Nd concentrations in the maize shoots. Inoculation with AMF also significantly decreased the concentration of certain heavy metals in the shoots and roots of maize and sorghum. These findings indicate that AMF can alleviate the effects of REE and heavy metal toxicity on plants and enhance the ability of plants to adapt to the composite adversity of REE in mine tailings.     

A Laboratory Study on Revegetation and Metal Uptake in Native Plant Species from Neutral Mine Tailings

Lygeum spartum, Zygophyllum fabago and Piptatherum miliaceum are typical plant species that grow in mine tailings in semiarid Mediterranean areas. The aim of this work was to investigate metal uptake of these species growing on neutral mine tailings under controlled conditions and their response to fertilizer additions. A neutral mine tailing (pH of soil solution of 7.1–7.2) with high total metal concentrations (9,100 and 5,200 mg kg^?1 Zn and Pb, respectively) from Southern Spain was used. Soluble Zn and Pb were low (0.5 and <0.1 mg l^?1, respectively) but the major cations and anions reached relatively high levels (e.g. 2,600 and 1,400 mg l^?1 Cl and Na). Fertilization caused a significant increase of the plant weight for the three species and decreased metal accumulation with the exception of Cd. Roots accumulated much higher metal concentrations for the three plants than shoots, except Cd in L. spartum. Shoot concentrations for the three plants were 3–14 mg kg^?1 Cd, 150–300 mg kg^?1 Zn, 4–11 mg kg^?1 Cu, and 1–10 mg kg^?1 As, and 6–110 mg kg^?1 Pb. The results indicate that neutral pH mine tailings present a suitable substrate for establishment of these native plants species and fertilizer favors this establishment. Metal accumulation in plants is relatively low despite high total soil concentrations.     

Interactions between earthworms, trees, soil nutrition and metal mobility in amended Pb/Zn mine tailings from Guangdong, China

This paper reports research that attempts to rehabilitate toxic Pb/Zn mine tailings, in Guangdong, China, to achieve a healthy functional soil that supports sustainable vegetation. We studied the effects of the earthworm Pheretima guillelmi on the growth of a woody legume Leucaena leucocephala on Pb/Zn mine tailings diluted with varying amounts of mineral soil in pot experiments. L. leucocephala grew successfully on tailings with a 25% (w/w) soil amendment, but P. guillelmi only survived and actively burrowed with a 50% soil amendment. The presence of earthworms improved the yield of plants by 10-30%. Whilst earthworms marginally increased available N and P in soil, they increased uptake of phosphorus (by about 10%) to above-ground plant tissues. Six-month-old plants were more sensitive than 10-month plants to metal stress. P. guillelmi increased bioavailable metal concentrations in the amended spoils, accompanied by a direct increase of metal uptake by the plants. Increased metal uptake by plants was largely due to the higher dry matter production stimulated by earthworm activity, but this increased the rate of metal uptake into plants from spoil by at least 16% and as much as 53%. These results demonstrate that we should broaden the ecological context of phytoremediation by considering the plant-soil-animal interactions that influence metal mobility.     

Incinerated Sewage Sludge Products as Amendments for Agricultural Soils: Leaching and Plant Uptake of Trace Elements

Preliminary leaching column and greenhouse plant uptake studies were conducted in two soils with contrasting characteristics amended with varying rates (0 to 148.3 Mg ha^?1) of incinerated sewage sludge (ISS) and weathered sewage sludge (WISS) to estimate the leaching losses of trace elements from the soils amended with incinerated sewage sludge by products and to evaluate the uptake and accumulation of these elements in various parts of Sorghum vulgaris var. sudanense Hitche. (“Sorgrass''), a Sorghum-Sudan grass hybrid. Results of this study indicated that leaching of Cr, Cd, Zn, Cu, Ni, Fe and Mn from soils amended with ISS and WISS increased with increasing rates of amendment. Results of the leaching column study further revealed greater leaching losses from coarse-textured soil compared to medium-textured soil and also from ISS amended soils than with WISS amended soils. Results further suggested that the type of element and the interaction between the element and soil properties affected the leachability of various trace elements. The uptake study indicated uptake and accumulation of trace elements by plant parts increased with increasing rates of amendments. Greater plant uptake and accumulation of trace elements were observed in plant parts grown in soils amended with ISS compared to that of WISS. Results also indicated a greater accumulation of trace elements in below ground part of the plants (roots) compared to that was observed in above ground parts (shoots). Limited data obtained from this one season preliminary studies demonstrated that incinerated sewage sludge products from wastewater treatment plants could be used as soil amendments at low application (no more than 24.7 Mg ha^?1) for optimum plant growth, and dry matter yield without resulting in substantial accumulation of metals in plant parts at concentrations above the recommended critical limits and without causing significant leaching losses of various trace elements. It is imperative that long-term field studies are necessary to evaluate the long-term impact of using these new products in leaching and accumulation of various trace elements in plants and soils.     

Metal Accumulation by Woody Species on Contaminated Sites in the North of France

Metal accumulation was investigated in a range of woody species that were planted on Cd-, Zn- and Pb- polluted sites in North of France. The study is unique in that we directly compare a large number of woody species (25). The highest accumulation of Zn and Cd was found in the Salicaceae family members with up to 950 mg Zn kg^?1 dry weight (DW) and 44 mg Cd kg^?1 DW in leaves of Populus tremula × Populus tremuloides. Zn content was positively correlated with Cd content, both in leaves and stems. Pb concentration was generally low and was species-independent. Oak and birch species accumulated more Mn as compared to other woody species. A seasonal variation in metal accumulation could be found. Although soil compositions and metal bioavailabilities differed amongst the experimental sites chosen in this study, variation of metal concentrations within a given species was small. High bioconcentration factors for poplar and willow suggested the high potential of these species over other woody species for metal accumulation. Taken together, these data suggest that poplar and willow species are good candidates for phytoremediation programmes.     

The Potential for Waste‐Derived Materials to Form Soil Covers for the Restoration of Mine Tailings in Ireland

Revegetation of mine tailings sites can require significant amounts of topsoil, the sourcing of which can be costly and have detrimental impacts. To address this problem at an Irish mine tailings site, engineered soils were created by mixing varying rates of glacial till with stockpiled peat and compost. Soil status was assessed using a range of soil parameters and vegetation growth characteristics and compared with locally sourced topsoil. Hordeum vulgare (Barley) germination and growth trials were assessed on engineered soils: compost with glacial till, peat with glacial till, compost/ peat with glacial till and topsoil. A range of soil quality parameters were examined including: nutrient status, dehydrogenase activity, metals availability and physical characteristics (bulk/particle density and porosity). Results demonstrate that compost derived soils yielded superior plant biomass and nutrient content, whilst peat derived treatments exhibited nutrient deficiency. Whilst the engineered soils offer potential as an alternative to sourcing topsoil for covering mine tailings, the phosphorus and metal content of composts should be assessed prior to inclusion. Copyright © 2015 John Wiley & Sons, Ltd.     

Evaluating the Suitability of MSW Compost as a Soil Amendment in Field Grown Tomatoes Part B: Elemental Analysis

Tomato plants were grown under field conditions in soil amended with 0, 25, and 50 tons/acre of source separated composted municipal solid waste (MSW). The leaves and fruit from these plants were sampled following a dual-stage nested design, and analyzed for 17 elements. Statistical analysis of the results showed that the Na and P contents increased and that the Cd and Be contents decreased in the fruits grown in the amended soil. In the leaves of tomato plants grown in amended soil the Na content increased, and the Cd, Cu, and Mn contents decreased compared to those grown in the control soil. The attenuation of the Cd, Cu, and Mn levels in the tomato tissues was attributed to increases in pH and organic matter in the compost amended soil.     

Potential of willow and its genetically engineered associated bacteria to remediate mixed Cd and toluene contamination

Purpose

The purpose of this study was to investigate if bacteria with beneficial properties that were isolated from willow growing on a metal-contaminated site can be further equipped with genes coding for a specific degradation pathway to finally obtain transconjugants that can be inoculated in willow to improve phytoremediation efficiency of mixed contaminations.

Materials and methods

Cultivable rhizosphere bacteria and root endophytes were isolated from willow (cv. Tora) growing on a metal-contaminated soil. All isolated strains were tested for their metal resistance and potential to promote plant growth. The two most promising strains were selected and were equipped with the pTOM plasmid coding for toluene degradation. Both transconjugants were inoculated separately and combined in willow cuttings exposed to mixed Cd–toluene contamination, and their effect on phytotoxicity, Cd uptake, and toluene evapotranspiration was evaluated.

Results and discussion

Many of the isolated strains tested positive for the production of siderophores, organic acids, and indole acetic acid (IAA) and showed increased Cd resistance. The Cd-resistant, siderophore-producing rhizosphere strain Burkholderia sp. HU001 and the Cd-resistant root endophyte Pseudomonas sp. HU002, able to produce siderophores, organic acids, and IAA, were selected as receptors for conjugation with the toluene-degrading Burkholderia vietnamiensis BU61 as a donor of the pTOM-TCE plasmid. Although inoculation with the individual transconjugant strains had no effect on plant growth and negatively affected Cd uptake, their combined inoculation resulted in an increased shoot biomass upon Cd–toluene exposure did not affect Cd uptake and strongly reduced evapotranspiration of toluene to the atmosphere.

Conclusions

In this study, inoculation of willow with a consortium of plant-associated bacteria equipped with the appropriate characteristics resulted in an improved phytoremediation of a mixed Cd–toluene contamination: the degradation of toluene was improved leading to a decreased toxicity and evapotranspiration, while Cd uptake and translocation were not affected.     

矸石添加对铜尾矿中香根草生长及生理生态的影响

为了探索矸石作为改良剂用于尾矿生态修复,通过盆栽试验,将矸石按一定比例(0,1%,2.5%,5%,10%和15%)添加入铜尾砂,基于铜尾砂理化性质变化,探索矸石对尾砂中香根草生理生态的作用特点。结果表明:矸石添加入铜尾砂后,提高了基质pH、有机质和营养元素含量,降低了有效态重金属浓度(Cd、Cu、Pb和Zn),改善了尾矿贫瘠环境。随矸石添加比例增加,香根草体内重金属浓度呈下降趋势,生物量和光合色素含量呈现低促高抑性变化。同时,可溶性蛋白质和脯氨酸含量随矸石添加比例增加而增加,MDA随添加比例增加而降低,低添加比例的矸石选择性提升了SOD和CAT酶活性,增强了香根草清除体内多余活性氧的能力。矸石加入铜尾砂可稳定铜尾矿中有效态重金属,也能在一定添加比例内,提高香根草抵御铜尾矿胁迫环境的能力。     

Effects of cover materials on leaching of constituents from dolomitic lead mine tailings

Five raised-bed test plots were used to study the effects of cover materials on the leaching of constituents from dolomitic Pb mine tailings over a 2-yr period. The cover materials studied were a fertilizer and seed mixture, anaerobically digested sewage sludge, loam and sod, and fallen leaves from silver maples (Acer Saccharinum); one plot was not covered. Fresh leachates and receiving pool waters were analyzed for ten metals, Si, P, inorganic anions, filterable organic carbon (FOC), and alkalinity. The mixture of fertilizer and seed decreased leaching of Pb and Zn during the first year. The leaf cover increased leaching of Pb during both years; this effect decreased as the leaves weathered. Sludge caused some increase in Pb leaching during the first year, and increased Cd leaching during both years. Concentrations of most leachate constituents decreased, and pH increased in the receiving pools. Concentrations of Pb remained higher in the receiving pool for the leaf-covered plot than in the other pools. Increases in leaching of Pb and Cd with a sludge cover were moderate, and the ability of the material to support plant growth on the tailings suggested that it may be a good medium for inducing growth of vegetative cover on the dolomitic tailings. Other organic materials may cause pronounced increase in the concentration of toxic trace metals in leachate from the tailings.     

Nitrogen availability to citrus seedlings from urea and from mineralization of citrus leaf or compost

A pot experiment was conducted using a Candler fine sand (hyperthermic, uncoated, Typic Quartzipsamments) amended with either citrus leaves or compost, to measure the nitrogen (N) mineralization and its availability to two citrus rootstock seedlings. A rapid increase in NH₄‐N concentration was evident in the soil amended with citrus leaves as compared to compost during the initial 14 to 20 d. Subsequently, the concentration of NH₄‐N decreased in the citrus leaves amended soil. The extractable NO₃‐N concentration was greater in the soil amended with citrus leaves as compared to compost, throughout the 270 d duration of the study. The N concentrations and N uptake by Cleopatra mandarin (CM) and Swingle citrumelo (SC) seedlings grown in citrus leaf amended soil were very similar to those in urea amended soil. Therefore, mineralization of N from dry ground citrus leaves was quite rapid. The N concentrations in both rootstock seedlings were much lower in the compost amended and unamended soils as compared to those in either citrus leaves or urea amended soils. Rapid mineralization of N from cirrus leaves added to sandy soil, resulting in an increased availability of N, suggested that the contribution of N from shed leaf mineralization must be considered while developing N rate recommendations for improving N use efficiency.     

Some interactions of cadmium with other elements in plants

Abstract

Cadmium in solution culture at 10^‐4 M decreased Mn concentrations in bush beans (Phaseolus vulgaris L. C.V. Improved Tendergreen) at both low and high concentrations of Mn (noncompetitive inhibition). When Mn was decreased, the concentrations of Fe and several other ions were simultaneously increased, particularly in leaves and roots. Toxicity due to the 10^‐6 M Cd and the 10^‐4 M Mn was additive in the experiment. When barley (Hordeum vulgare L. Atlas57)was grown in amended soil, 15μg Fe as DTPA (diethylene triamine pentaacetic acid) per g soil resulted in increased uptake of Cd and in somewhat greater yield depression for soil pH of 3.9, 6. 0, and 7.6. Acidification of soil without DTPA also increased Cd uptake to high levels with associated yield decrease. The Cd decreased the uptake of Mn and Cu most when CaCO₃ had also been added to the soil. When salts were added to soil with Cd before bush beans were grown, KCl (200 μg K/g soil), and equivalent KH₂PO₄ increased Cd concentrations of leaves while CaSO₄ and KCl did so for roots. In bush beans with different levels of Cd and Zn, there were no yield interactions, but some interactions of Cd on Zn concentrations in leaves, stems, and roots at the high Zn level.