Phytostabilization potential of ornamental plants grown in soil contaminated with cadmium

In a greenhouse experiment, five ornamental plants, Osmanthus fragrans (OF), Ligustrum vicaryi L. (LV), Cinnamomum camphora (CC), Loropetalum chinense var. rubrum (LC), and Euonymus japonicas cv. Aureo-mar (EJ), were studied for the ability to phytostabilization for Cd-contaminated soil. The results showed that these five ornamental plants can grow normally when the soil Cd content is less than 24.6 mg·kg^?1. Cd was mainly deposited in the roots of OF, LV, LC and EJ which have grown in Cd-contaminated soils, and the maximum Cd contents reached 15.76, 19.09, 20.59 and 32.91 mg·kg^?1, respectively. For CC, Cd was mainly distributed in the shoots and the maximum Cd content in stems and leaves were 12.5 and 10.71 mg·kg^?1, however, the total amount of Cd in stems and leaves was similar with the other ornamental plants. The enzymatic activities in Cd-contaminated soil were benefited from the five tested ornamental plants remediation. Soil urease and sucrase activities were improved, while dehydrogenase activity was depressed. Meanwhile, the soil microbial community was slightly influenced when soil Cd content is less than 24.6 mg·kg^?1 under five ornamental plants remediation. The results further suggested that ornamental plants could be promising candidates for phytostabilization of Cd-contaminated soil.     

Arsenic accumulation of common plants from contaminated soils

A pot experiment was conducted to investigate the relationship between soluble concentrations of arsenic (As) in soil and its accumulation by maize (Zea mays), English ryegrass (Lolium perenne), rape (Brassica napus) and sunflower (Helianthus annuus) on two different soils: a calcareous Regosol (silty loam) and a non-calcareous Regosol (sandy loam). Arsenic (Na₂HAsO₄·7H₂O) was applied to obtain comparable soluble As concentrations in the two soils. In both soils, soluble As concentrations, extracted with 0.1 M NaNO₃, were found to correlate better with As concentrations in plants after 4 month of growth than total soil concentrations, extracted with 2 M HNO₃. With all four plant species, the relationship between the soluble As concentration in the soil and As that in the plants was non- linear, following Michaelis-Menten kinetics. Similar soluble As concentrations in the two soils did not result in a similar As concentration in the plants. Except for maize, arsenic transport from roots to shoots was significant, resulting in As concentrations in the leaves and grains above the Swiss tolerance limits for fodder and food crops (4 and 0.2 mg As kg^–1, respectively). Based on these results we suggest that beside As solubility, P availability and P demand, which are plant specific, have to be taken into account to predict the uptake of As by crop plants from As contaminated soils and to predict the risk of arsenic entering into the food chain.     

花卉植物应用于污染土壤修复的可行性研究

植物修复是解决污染土壤问题的有效途径之一,而已报道的超积累植物的种类非常有限.如果能从物种繁多的花卉植物中筛选出修复植物,不但能够弥补这一不足,而且还能在美化环境的同时,产生一定的经济效益.从植物修复的重要性和修复植物的筛选出发,概括了修复植物的判断标准及基本特征.通过描述花卉植物资源及其在环境保护中的作用,列举花卉植物与其它植物相比的优势,分析花卉植物的耐性、积累性和修复类型,探讨花卉植物应用于污染土壤修复实践的可行性.从花卉中筛选超积累植物,将为污染土壤的修复工作提供的生物材料.     

Availability and toxicity of cadmium to forage grasses grown in contaminated soil

It is important to know the mechanisms for forage development, especially those related to the tolerance of potentially toxic elements, when considering their use in phytoremediation in heavy metal contaminated areas. In this study, we evaluated plant growth, concentration, and the availability of cadmium (Cd) for forage grasses (Panicum maximum Jacq. cv. Aruana and cv. Tanzânia; Brachiaria decumbens cv. Basilisk; Brachiaria brizantha cv. Xaraés and cv. Marandu) cultivated in Cd contaminated soils. The experiments were performed under greenhouse conditions over a 90-day evaluation period, and the Cd rates were 2, 4, and 12 mg/kg of soil. The relative growth rate of the forage grasses decreased as Cd rates increased, and the following descending order of susceptibility was observed: Marandu > Xaraés > Aruana > Tanzânia > Basilisk, with regard to phytotoxicity in these plants. The forage Cd concentration increased in line with increases in the Cd rates. Cd contents extracted by Mehlich-1 and by diethylenetriaminepentaacetic acid presented high positive correlation with forage relative growth. The forage plants did not block Cd entry into the food chain because they were not capable of limiting Cd absorption.     

高生物量经济植物修复重金属污染土壤研究进展

植物修复是重金属污染土壤修复的重要方法之一。利用高生物量经济植物修复重金属污染土壤,能够兼顾生态和经济效益,具有很大的应用前景。本文系统分析了植物修复现状及存在的问题,提出利用高生物量经济植物修复重金属污染土壤的优势,总结了近年来利用高生物量经济植物吸收重金属的研究进展,探讨了改善高生物量经济植物修复重金属污染土壤效率的方法,以期为提高植物修复经济效益、促进植物修复广泛应用提供参考。     

Effect of fluoride supply on fluoride concentrations in five pasture species: Levels required to reach phytotoxic or potentially zootoxic concentrations in plant tissue

Recent findings have highlighted the possibility of increased fluoride (F) concentrations in herbage through F taken up from soil via the plant root. This paper aimed to assess the risk of F concentrations reaching phytotoxic or zootoxic concentrations in pasture plants. Five plant species commonly found in improved pastures in Australia, the sown species subterranean clover (Trifolium subterranean) and cocksfoot (Dactylis glomerata), and weeds barley grass (Hordeum leporinum), scotch thistle (Onopordum acanthium) and sorrel (Rumex acetosella) were grown in complete nutrient solutions with graded levels of added F to determine the effects of F⁻ activity in solution on phytotoxicity and uptake of F by their roots. A model was developed using data from these solution culture experiments and data from the literature. The model assessed uptake of F by plants grown over a range of soil pH values and determined the risk of F taken up through the plant roots reaching phytotoxic concentrations, or concentrations potentially injurious to grazing animals, in the plant shoots. Modelling data suggested that the plants studied would not accumulate phytotoxic concentrations of F in shoots or concentrations of F deleterious to grazing animals through root uptake in neutral pH agricultural soils. The risks from F addition to soils in phosphatic fertilisers leading to reduction in pasture growth or animal health are therefore low. However, in highly F-polluted soil, as the soil becomes more acidic or alkaline, the risk of zootoxic concentrations of F in shoots of plants would increase. This revised version was published online in June 2006 with corrections to the Cover Date.     

Availability and zinc accumulation in forage grasses grown in contaminated soil

Zinc is an important micronutrient to plant growth, but when present in large quantities it can become a toxic element to plants. This study was aimed to evaluate the growth, concentration, accumulation and availability of Zn to forage grasses (Megathyrsus maximus cvs. Aruana and Tanzania, Urochloa brizantha cvs. Xaraés and Marandu and Urochloa decumbens cv. Basilisk) cultivated in Zn contaminated soils. The experiments were conducted under greenhouse conditions over a 90-day evaluation period, and Zn rates were 0, 100, 300 and 900 mg kg^?1 of soil. The Zn rates in soil caused growth reduction in all evaluated forage grasses. The cultivar Aruana was generally more tolerant to Zn, while the Marandu was generally more susceptible to the addition of Zn. The cultivar Aruana proved to be superior to others due to its higher growth and higher critical level toxicity of Zn. None of the forage grasses evaluated can be considered a Zn hyperaccumulator. The extraction order was DTPA at pH 7.3 < Mehlich-1 < USEPA 3051 < USEPA 3052 in the soil independent of forage grasses cultivation. The USEPA 3051 extractor was similar to Mehlich-1 in predicting the availability of Zn in soil.     

淹水条件下控释氮肥对污染红壤中重金属有效性的影响

采用淹水培养方法研究了不同氮水平(100、200和400 mg/kg,分别记为1、2、3)下普通尿素(PU)、硫包膜尿素(SCU)、树脂包膜尿素(PCU)和硫加树脂双层包膜尿素(SPCU)对污染红壤中Cd、Pb、Cu、Zn有效性的影响.结果表明,不同包膜尿素对土壤pH值和水溶性SO42-含量有较大影响.各施氮处理红壤pH值随着施氮量的增加(除5d时PU和60 d时SCU)而增加,不同包膜尿素对土壤中水溶性SO42-含量有较大影响,在同一施氮水平下不同包膜尿素处理间土壤pH值和土壤中水溶性SO42-含量差异较大.60 d培养期间PU、SCU、PCU和SPCU处理pH值比对照分别升高0.17-0.38、0.08-0.27、0.07-0.36和0.10-0.21;水溶性SO42-含量PU、SCU和PCU处理比对照分别升高39.5％-157.3％、40.9％-94.5％和7.55％-55.8％,而SPCU处理降低5.67％-90.7％.不同尿素类型和氮肥的施用量对红壤Cd、Pb、Cu和Zn有效性的影响均存在显著差异.60 d培养期间红壤有效态Cd含量以树脂包膜尿素100 mg N/kg下最低,其有效态Cd含量比对照显著降低20.7％-69.8％;有效态Pb、Cu和Zn含量以普通尿素400 mg N/kg下最低,其有效态Pb、Cu和Zn含量比对照分别显著降低17.0％-54.2％、18.5％-34.6％和15.6％-59.5％.随施氮量提高,PU处理有效态Cd含量先升高后降低,有效态Pb、Cu和Zn含量逐渐降低;SCU处理有效态Pb含量逐渐降低,有效态Cd、Cu和Zn含量变化规律不一致;PCU处理有效态Cd含量逐渐升高,有效态Pb、Cu和Zn含量变化规律不一致;SPCU处理有效态Cd、Pb、Cu和Zn含量逐渐降低.有效态Pb和Zn含量与pH值和水溶性SO42-含量呈显著负相关,有效态Cd与水溶性SO42-含量呈显著正相关.在多重金属污染红壤中,可考虑不同控释氮肥的配合使用,降低土壤中重金属的有效性.     

佛山市几种绿地植物氟化物时空累积特征

对佛山市的防护绿地、公园绿地、生产绿地及附属绿地等城市绿地系统中的大叶榕、细叶榕、芒果、白兰、垂叶榕和尖叶杜英的叶片和各绿地系统中的大气氟化物含量进行了测定,并对其相互关系进行了研究。结果表明:四季中各绿地系统的大气氟化物含量均值的大小依次为防护绿地的工业区、交通区、附属绿地、生产绿地和公园绿地;工业区的大气氟化物浓度约为公园绿地的3.4倍,不同城市绿地系统的1、2年生植物叶片含氟量均随时间的延长而逐渐增加;大气氟化物与叶片含氟量之间存在密切相关性,反映了植物氟化物的空间累积特征,其中细叶榕和垂叶榕的1年生和2年生叶片、芒果的1年生叶片、白兰的2年生叶片中的氟化物浓度能较好地表征城市绿地系统中大气氟化物的浓度。     

Carbon and nitrogen allocation shifts in plants and soils along aridity and fertility gradients in grasslands of China

Plant carbon (C) and nitrogen (N) stoichiometry play an important role in the maintenance of ecosystem structure and function. To decipher the influence of changing environment on plant C and N stoichiometry at the subcontinental scale, we studied the shoot and root C and N stoichiometry in two widely distributed and dominant genera along a 2,200‐km climatic gradient in China's grasslands. Relationships between C and N concentrations and soil climatic variables factors were studied. In contrast to previous theory, plant C concentration and C:N ratios in both shoots and roots increased with increasing soil fertility and decreased with increasing aridity. Relative N allocation shifted from soils to plants and from roots to shoots with increasing aridity. Changes in the C:N ratio were associated with changes in N concentration. Dynamics of plant C concentration and C:N ratios were mainly caused by biomass reallocation and a nutrient dilution effect in the plant‐soil system. Our results suggest that the shifted allocation of C and N to different ecosystem compartments under a changing environment may change the overall use of these elements by the plant‐soil system.     

Potential of Salix as phytoextractor for Cd on moderately contaminated soils

Biomass production and Cd uptake in Salix (willow) is generally high. The aim of this study was to quantify the amounts of Cd in different plant and soil compartments in commercial Salix stands grown on different soil types and to use these data for estimation of the long-term effects of Cd removal by Salix at stem harvest on the soil Cd content by calculating Cd balances. Ten commercial short rotation willow coppice stands, planted with clone 78183 of Salix viminalis (L.) were investigated in order to include three different soil types with respect to pH. Stands with high stem biomass production generally had lower Cd concentrations in the plant and grew on more alkaline soils with low Cd availability when compared to stands with low stem biomass production. The highest output of Cd by Salix is therefore not necessarily achieved by stands with the highest yields or the highest Cd concentrations, as both these parameters have to be considered. The net removal of Cd from the plough layer by the Salix crop under different conditions varied between 2.6 and 16.5 g Cd ha^–1 year^–1. The long-term effects of Salix cultivation on soil Cd content, i.e. after 6–7 cutting cycles (25 years), were calculated and we reached the conclusion that there is a high potential in Salix to remove significant amounts of Cd at stem harvest. Salix can therefore presumably be used to counteract Cd pollution of agricultural soils in Sweden provided that the Cd in furnace ashes is taken care of.     

Heavy metals accumulation and distribution in durum wheat and barley grown in contaminated soils under Mediterranean field conditions

Abstract

In the framework of a phytoremediation project in the Apulia region (Italy) a field experiment was carried out in multi-metal contaminated soils. The accumulation and distribution of metals in different plant parts of durum wheat and barley were studied. Further, the application of Bacillus licheniformis strain BLMB1 to soil was evaluated as a means to enhance metal accumulation in plants. The translocation and the bioconcentration factors indicated that wheat and barley do not act as metal accumulators in the field conditions tested, thus phytoextraction by these species would not be recommended as a soil remediation alternative. Application of B. licheniformis improved the accumulation of all metals in roots of wheat and barley, and increased Cd, Cr, and Pb contents in the shoots of barley. Low health risk for humans and animals was evaluated to exist if straw and grain from both cereal crops grown in these contaminated sites are consumed.     

Characterization of cadmium desorption in soils and its relationship to plant uptake and cadmium leaching

Experiments on Cd desorption were conducted with a range of water-to-soil ratios to assess the desorption characteristics of Cd in soils and the availability of Cd for absorption by plant roots and leaching to groundwater, Soil samples were collected from sites contaminated by a former Pb and Zn smelter, by sewage irrigation, or with artificial additions of Cd and sewage sludge. Glasshouse pot experiments were conducted in which the yield and Cd uptake of crop plants were determined. Cadmium leached from soil columns was also studied using soil lysimeters. The soil solution Cd concentration decreased with increasing solution-to-soil ratio and followed a negative power function. Two constants obtained from logarithmic linear regression were identified. The intercept (C₁) was Cd concentration in the soil solution where the solution/soil ratio was equal to 1 and this constant was the intensity factor of the initial element supply in the soil. The slope (a) showed a decreasing trend for Cd concentration in the soil solution which was related to the soil buffering capacity. A corrected concentration (C₁/a) is proposed for expressing soil desorption ability. This combined index was significantly correlated with Cd uptake by plants and also with Cd leached from soil columns.     

Hydraulic redistribution: limitations for plants in saline soils

Hydraulic redistribution (HR), the movement of water from wet to dry patches in the soil via roots, occurs in different ecosystems and plant species. By extension of the principle that HR is driven by gradients in soil water potential, HR has been proposed to occur for plants in saline soils. Despite the inherent spatial patchiness and salinity gradients in these soils, the lack of direct evidence of HR in response to osmotic gradients prompted us to ask the question: are there physical or physiological constraints to HR for plants in saline environments? We propose that build‐up of ions in the root xylem sap and in the leaf apoplast, with the latter resulting in a large predawn disequilibrium of water potential in shoots compared with roots and soil, would both impede HR. We present a conceptual model that illustrates how processes in root systems in heterogeneous salinity with water potential gradients, even if equal to those in non‐saline soils, will experience a dampened magnitude of water potential gradients in the soil–plant continuum, minimizing or preventing HR. Finally, we provide an outlook for understanding the relevance of HR for plants in saline environments by addressing key research questions on plant salinity tolerance.     

Genetic diversity in perennial ryegrass and white clover among old Dutch grasslands as compared to cultivars and nature reserves

To support conservation policies for old Dutch grasslands that are still in agricultural use, morphological variation and AFLP-based (amplified fragment length polymorphism-based) genetic diversity was studied in perennial ryegrass and white clover populations and compared with the diversity in reference varieties. In addition, AFLP variation was also studied in grasslands located in nature reserves. From principal component analysis (PCA), it appeared that date of ear emergence in perennial ryegrass and characters related to plant vigour in white clover were the main morphological characters separating the reference varieties from the old Dutch grassland populations, and some of the grassland populations from each other. In both species, intrapopulation variation was lower for the reference varieties. Lower heterogeneity within the reference varieties was also found in the AFLP analysis. All common AFLP's observed in old Dutch grasslands could also be found in the reference varieties and nature reserves. Only a small number of low-frequency alleles found in old Dutch grasslands were absent from the other two groups. However, band frequencies of markers could vary considerably between populations, which may have been caused by selection. Analysis of the AFLP data by PCA distinguished the majority of reference varieties from the old Dutch grasslands, and showed genetic differentiation only between some grasslands. Comparison of old Dutch grasslands with grasslands in nature reserves indicated that basically the same range of genetic variation is covered by the two groups. Our study indicates that the Netherlands harbour a more or less continuous population for major parts of the diversity of perennial ryegrass and white clover. It was concluded that no specific conservation measures are presently needed to maintain genetic diversity of perennial ryegrass and white clover occurring in old Dutch grasslands.     

Removal of fluoride contamination in water by three aquatic plants

Phytoremediation, popularly known as ‘green technology’ has been employed in the present investigation to examine the potential of fluoride removal from water by some aquatic plants. Fluoride contamination in drinking water is very much prevalent in different parts of the world including India. Batch studies were conducted using some aquatic plants e.g., Pistia stratiotes, Eichhornia crassipes, and Spirodela polyrhiza which profusely grow in natural water bodies. The experimental data exhibited that all the above three aquatic floating macrophytes could remove fluoride to some relative degree of efficiency corresponding to initial concentration of fluoride 3, 5, 10, 20 mg/l after 10 days exposure time. Result showed that at lower concentration level i.e., 3 mg/L removal efficiency of Pistia stratiotes (19.87%) and Spirodela polyrhiza (19.23%) was found to be better as compared to Eichhornia crassipes (12.71%). Some of the physiological stress induced parameters such as chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, total protein, catalase, and peroxidase were also studied to explore relative damage within the cell. A marginal stress was imparted among all the plants for lower concentration values (3 mg/L), whereas at 20 mg/l, maximum damage was observed.     

City refuse compost as a phosphorus source to overcome the P-fixation capacity of sesquioxide-rich soils

In sesquioxide-rich soils of tropical and subtropical areas and volcanic-ash soils with high levels of active Al(Fe), large amounts of phosphate fertilizers are needed to overcome their high P-fixation capacity (quenching strategy). A greenhouse pot experiment has been used to evaluate the effectiveness of city refuse compost (CRC) as a P-source for these variable-charge soils, compared to inorganic P. Mature CRC and K₂HPO₄ were applied at rates equivalent to 125, 250, 375, 500 and 625 kg P ha^–1 to a ferrallitic soils from Tenerife Island (Andeptic Paleudult) with a high content in active Al+Fe (4.82%) and a high P-fixation capacity (87%). Perennial ryegrass (Lolium perenne L.) was grown in pots and plants were harvested at regular intervals after seedling emergence. CRC increases plant P concentration and soil labile-P proportional to the applied rate. The best results were obtained from a compost application of 30 t ha^–1 equivalent-rate, after a residence time of at least three months. An important residual effect in the supply capacity of P in relation to the phosphate fertilizer was also observed. The relative agronomic effectiveness (RAE) in comparison to K₂HPO₄ was 66% after 6 months, considering P uptake + soil labile-P. The soil P-fixation capacity was significantly reduced from a compost application of 40 t ha^–1 equivalent-rate. Competition in adsorption between organic ligands and phosphate, in combination with net mineralization of organic P in compost, might account for the high RAE value obtained. The main conclusion is that the city refuse compost could be a suitable P-amendment for resquioxic soils due to its high RAE, and the residual effect on P-supply. ei]H. Lambers     

Effect of selected soil factors on chlorosis of peanut plants grown in calcareous soils in Cyprus

In 1986 and 1987 surveys were conducted of 34 (1986) and 35 (1987) peanut (Arachis hypogaea L.) fields in which the plants showed various degrees of chlorosis. In the areas concerned, plant appearance was classified according to a chlorotic index and corresponding soil samples were taken and analysed for CaCO₃, pH, NO₃–N and DTPA-extractable Fe in 1986 and for CaCO₃, NO₃–N and active lime in 1987.Regression analyses showed that CaCO₃, active lime and NO₃–N were positively correlated, while DTPA-extractable Fe was negatively correlated, with the chlorosis problem. The critical levels above which plants were chlorotic were 20 to 25% CaCO₃ and 10% active lime. Plants began to be chlorotic when DTPA-extractable Fe was below 2.5 mg·kg^–1. The soil factors examined explained about 60% of the variability in plant chlorosis.