Transport of cadmium from soil to grain in cereal crops: A review

Due to rapid urbanization and industrialization, many soils for crop production are contaminated by cadmium(Cd), a heavy metal highly toxic to many organisms. Cereal crops such as rice, wheat, maize, and barley are the primary dietary source of Cd for humans, and reducing Cd transfer from soil to their grains is therefore an important issue for food safety. During the last decade, great progress has been made in elucidating the molecular mechanisms of Cd transport, particularly in rice. Inter-and intraspecific variations in Cd accumulation have been observed in cereal crops. Transporters for Cd have been identified in rice and other cereal crops using genotypic differences in Cd accumulation and mutant approaches. These transporters belong to different transporter families and are involved in the uptake, vacuolar sequestration, root-to-shoot translocation, and distribution of Cd. Attempts have been made to reduce Cd accumulation in grains by manipulating these transporters through overexpression or knockout of the transporter genes, as well as through marker-assisted selection breeding based on genotypic differences in Cd accumulation in the grains. In this review, we describe recent progress on molecular mechanisms of Cd accumulation in cereal crops and compare different molecular strategies for minimizing Cd accumulation in grains.     

Applications of fertilizer cations affect cadmium and zinc concentrations in soil solutions and uptake by plants

A pot experiment was conducted to study changes over time of Cd and Zn in soil solution and in plants. Radish was grown in a soil which had been contaminated with heavy metals prior to 1961. Constant amounts of a fertilizer solution (NH₄NO₃, KNO₃) were added daily. Soil solution was obtained at intervals by displacement with water. The cumulative additions of small amounts of fertilizers were made equal to the plants' requirements at the final harvest but were found to exceed them during most of the experiment. Excess fertilizers caused substantial increases of major (K, Ca, Mg) and heavy-metal (Cd, Zn) ions in soil solutions and a decrease in soil pH, probably due to ion-exchange mechanisms and the dissolution of carbonates. Uptake of Cd and Zn into leaves was correlated with the mass flow of Cd (adjusted r²= 0.798) and Zn (adjusted r²= 0.859). Uptake of K, Ca and Mg by the plants was independent of their concentrations in solution. It is concluded that, in order to study effects of plants on heavy-metal availability and obtain soil solution that has not been altered by fertilizer ions, nutrients must be added according to the needs and growth of the plants. This could be achieved by linking fertilizer additions to the rate of transpiration, as nutrient uptake and transpiration were closely correlated in this experiment.     

Chemical forms of cadmium in a calcareous soil treated with different levels of phosphorus and cadmium and planted to spinach

The objective of the investigation was to evaluate the effect of applied phosphorus (P) and cadmium (Cd) on Cd chemical forms determined by sequential extraction and the relationship between these forms and plant responses, i.e., dry weights, concentration, and total uptake of Cd and P in a greenhouse experiment. Treatments consisted of five levels of Cd (5, 10, 20, 40 and 80 mg kg^?1 soil as cadmium sulfate) and four levels of P (0, 15, 30 and 60 mg kg^?1 soil as monocalcium phosphate), which were added to the soil and left to equilibrate for 1 month under greenhouse conditions. Spinach seeds (Spinacea oleracea L., cv Viroflay) were sown and then grown for 8 weeks. The chemical composition in the aerial part of the pant and soil was determined. Application of Cd decreased plant dry matter and increased Cd concentration in the plant, whereas at each level of applied Cd, P increased plant dry matter and decreased plant Cd concentration. All chemical forms of Cd in soil, as determined by a fractionation method, were increased following Cd application, the highest being the carbonatic form. Phosphorous application decreased exchangeable and carbonatic forms of Cd, whereas it increased other forms.     

不同磷水平下玉米和小麦植株亚细胞中镉的积累

Corn and wheat plants were grown in a nutrient culture solution at four levels of phosphorus (0,0.12,0.60 and 3.0mmol L^-1) and two levels of cadmium(0 and 4.0umol L^-1) in greenhouse for a 18-day period.The concentrations of phosphorus and cadmium in cell wall,cytoplasm and vacuoles of roots and leaves were examined by cell fractionation techniques.With increasing phosphorus in medium,the contents of P in cell wall,cytoplasm and vacuoles of corn and wheat roots and leaves increased.The highest content of P was observed in cell wall,next in vacuoles,and the lowest in cytoplasm.The wheat subcellular fractions in both roots and leaves hab higher concentrations of phosphorus than those of corn.Increasing phosphorus in medium significantly inhibited the intracellular Cd accumulation in both species,However,at P concentration up to 3.0mmol L^-1,the Cd content in cell wall was increased.Increasing phosphorus resulted in reduction of the subcellular Cd content in cell wall was increased.Increasing phosphorus resulted in reduction of the subcellualr Cd content in corn and wheat leaves.Compared with corn,the wheat roots had a higher Cd content in the cell wall and vacuoles and a lower in cytoplasm,while in leaf subcellular fractions the wheat cell had a higher Cd content in its vacuoles and a lower one in its cytoplasm,The results indicate that phosphorus may be involved in sequestration of Cd ionic activity in both cell wall and vaculoes by forming insoluble Cd phosphate.     

Oxidative stress response in spinach plants induced by cadmium

In this work we studied the effect of cadmium (Cd) (25 μM), in spinach plants (Spinacea oleracea) growing in nutrient solution, for 1, 2 and 7 days. Spinach growing in the contaminated solution showed a decrease in biomass, chlorophyll content and an increase in malondialdehyde (MDA) content, showing that photosynthetic apparatus was affected and lipid peroxidation occurred. The main defence mechanisms against the induced oxidative stress were the activation of catalase, glutathione reductase and guaiacol peroxidase. Glutathione reductase activity suggests that glutathione is involved in the response against Cd toxicity. The uptake of zinc (Zn), potassium (K), iron (Fe) and copper (Cu) was affected, mainly at the higher exposition times. Spinach leaves showed no signs of toxicity and looked healthy although containing up to 35 mg kg^?1 dry weight (DW) of Cd. This can present a food security issue as there is no visible indication of the high amounts of Cd in the edible parts of the plant.     

应用田间行走式红外光谱进行土壤碳含量估测研究

对应用田间行走式设备获取的土壤红外光谱数据,通过特征变换和特征选择相结合,以提高所建立土壤碳校正模型的预测精度。首先应用独立成分分析（ICA）、主成分分析(PCA)和小波分析(WA)对土壤红外光谱数据进行特征变换,然后分别应用无信息变量消除法(UVE)、连续投影算法(SPA)、无信息变量消除结合连续投影算法(UVE-SPA)、基于遗传算法和偏最小二乘法的变量选择法(GA-PLS)来进行特征选择,基于所选择的特征建立了土壤碳校正模型。结果表明,通过ICA进行特征变换,然后进行特征选择,可以建立比直接对光谱数据进行波长选择精度更好的预测模型;而WA或PCA与特征选择方法结合,只能获得与对光谱数据直接进行波长选择相近的效果。因此,针对田间条件下通过行走式设备获得的光谱数据由于受复杂的环境条件下干扰多的情况,可以将ICA与特征选择方法结合起来对光谱数据进行特征变换和选择,以建立更可靠的土壤碳含量预测模型。     

Stabilization of cadmium in polluted soil using palygorskite-coated nanoscale zero-valent iron

Journal of Soils and Sediments - The palygorskite-coated nanoscale zero-valent iron (PAL-nZVI) was synthesized and used in the remediation of Cd-contaminated soils. The function of PAL-nZVI on...     

Removal of cadmium from aqueous solution by a soil containing magnesite

Removal of Cd (II) from aqueous solution by a soil containing magnesite and thermal activated soil containing magnesite was investigated. Maximum activation temperature was determined at 700°C for 2?h and maximum adsorption capacities were determined as 4.20?mg/g for natural magnesite, 38.91?mg/g for thermal activated magnesite at 25°C respectively. Equilibrium contact time of cadmium was determined for 2?h. Adsorption of Cd (II) on soil containing magnesite conforms to Langmuir's isotherm.     

Noticeable increase in cadmium absorption by zinc deficient rice plants

The uptake and transport of cadmium were studied using zinc deficient rice plants. As a result, these plants absorbed and transported cadmium more rapidly than normal rice plants. A zinc deficiency might bring about physiological changes which significantly increase the cadmium accumulation in the roots and its transport into the shoots.     

Remediation efficacy of Sedum plumbizincicola as affected by intercropping of landscape plants and oxalic acid in urban cadmium contaminated soil

Journal of Soils and Sediments - Intercropping is a promising technique for remediation of soils contaminated with heavy metals. Organic acids can increase the availability of heavy metals in soil....     

Estimation of microbial biomass and activity in soil using microcalorimetry

Relationships between the rate of heat output from soil, the rate of respiration and the soil microbial biomass were investigated for 25 soils from northern Britain. The rate of heat output, measured in a Calvet microcalorimeter at 22°C, correlated well with the rate of carbon dioxide respiration. The average amount of heat evolved per cm³ of gas respired. 21.1 J cm^?3, suggests that the biomass metabolism was largely aerobic. The rate of heat output per unit of total microbial biomass was remarkably uniform over a wide range of soils, but showed differences depending upon whether the soil had been stored or amended. Mineral soils that had been stored at 4°C had the lowest heat output, 12.0 mW g^?1 biomass C, compared with a mean of 20.4 mW g^?1 biomass C for freshly-collected soils. Amendment with glucose (0.5% w/w) caused an immediate increase in respiration and heat output, up to 59.4 mW g^?1 biomass C for stored soils and 188.2 mW g^?1 biomass C for freshly collected soils. There was a consistent relationship between the biomass and the rate of heat output from freshly collected and amended mineral and organic soils which gave a linear fit using log transformed data: y= 0.6970+ 1.025x (r= 0.98, P < 0.001) (y=log₁₀ biomass C, μgC g^?1; x=log₁₀ rate of heat output at 22°C, μW g^?1). The overall relationship between biomass and the rate of heat output for all the amended samples was: 1 g biomass C= 180.05 ± 34.61 mW.     

溶磷菌剂对施磷复垦土壤无机磷形态及油菜磷吸收的影响

  目的  通过分析攀西高原不同轮作模式对土壤肥力和phoD基因群落结构的影响,以期深入认识该生境下土壤磷素循环机制,建立合理的轮作制度。  方法  以攀西高原五种不同轮作制度下的休闲期土壤为研究材料,通过化学分析和高通量测序技术对土壤理化性质以及土壤中phoD基因群落结构与多样性进行研究。  结果  不同轮作制度处理下,相较于撂荒处理,土壤有效磷含量显著提高,全氮、碱解氮、有机碳含量显著降低（P < 0.05）。土壤中酸性磷酸酶活性（Acid phosphatase, ACP）显著高于碱性磷酸酶（Alkaline phosphatase, ALP）和中性磷酸酶（Neutral phosphatase, NP）,且在大麦－烤烟轮作制度中最高（13358 U g⁻¹）。就phoD基因的shannon多样性指数而言,在大麦－烤烟轮作制度下最高,而在苦荞－烤烟轮作下最低。不同轮作制度下phoD群落结构差异明显,变形菌门（Proteobacteria）、放线菌门（Actinobacteria）是不同轮作模式的主要门类,慢生根瘤菌(Bradyrhizobium)为主要优势属。冗余分析显示,有机碳、pH是该生境下驱动phoD基因群落结构变化的重要理化因子。  结论  与撂荒相比,轮作明显改变了土壤肥力和磷酸酶活性,形成了不同的土壤phoD基因群落结构。五种轮作制度中以苦荞－烤烟轮作对phoD基因多样性指数影响最为显著,大麦－烤烟轮作对土壤养分含量和碱性磷酸酶活性影响最大。     

Estimation of soil salinity in semi‐arid land using a geostatistical model

Soil salinity is one of the great problems in arid and semi‐arid environments. The estimation and prediction of spatial soil salinity may be considered as a stochastic process, observed at irregular locations in space. Environmental variables usually show spatial dependence among observations which is an important drawback to traditional statistical methods. Geostatistical techniques that analyse and describe the spatial dependence and quantify the scale and intensity of the spatial variation, provides spatial information for local estimation of soil salinity. In this paper we propose a Gaussian Spatial Linear Mixed Model (GSLMM), which involves a non‐parametric term, accounting for a deterministic trend given by exogenous variables, and a parametric component defining the purely spatial random variation, possibly due to latent spatial processes. We focus here on the analysis of the relationship between soil electrical conductivity as a parameter related directly to soil salinity as well as sodium content (sodicity) to identify spatial variations in these parameters. This kind of methodology is demonstrated as a useful tool for environmental land management. Copyright © 2007 John Wiley & Sons, Ltd.     

米渣蛋白对镉的吸附效果及其对土壤中镉的钝化作用研究

为探究米渣蛋白对水溶液中镉的吸附效果及米渣对土壤中镉活性的钝化效果,该研究首先用米渣蛋白在水溶液中对镉进行吸附、用盐酸解吸,并用Langmuir、Freundlich等温吸附方程来拟合米渣蛋白在水溶液中对镉的吸附过程,用动力学方程研究米渣蛋白与镉结合的机理,并根据线性关系从准一级、准二级吸附动力学方程中筛选更接近吸附动力的拟合方程。其次,通过周期取样,用Tessier分步连续提取法测定并探究米渣对土壤中镉的钝化能力。研究结果表明:在不同初始质量分数的镉溶液中米渣对镉的最大吸附量13.28mg/g,用盐酸解吸各初始质量分数下结合的镉,解吸率均达到90%以上。同时,Langmuir和Freundlich等温方程均能拟合米渣蛋白在水溶液中对镉的吸附过程,且R2达到0.99以上;准一级动力学、准二级动力学方程拟合结果是,拟合出的准二级动力学方程线性更好,米渣蛋白对镉的吸附动力更符合准二级动力学方程。土壤中镉钝化试验表明:加入米渣后,28d内土壤中镉的钝化效果较好,可能是由于米渣中的蛋白改变了土壤中镉的存在状态并降低镉的活性所致。该研究结果为米渣的应用提供新的思路,可为其在废水除镉、镉污染土壤的修复等方面应用提供理论依据。     

温室内香蕉树蒸腾量预报的试验研究

在温室内研究了香蕉树蒸腾量和小气候的关系，用5种方法计算了温室内的参考作物腾发量，用20 cm蒸发皿测定温室内的水面蒸发力，并和测定的香蕉树蒸腾量进行对比。试验结果显示香蕉树蒸腾量和蒸发皿水面蒸发量的回归系数(R²)最高，为0.94，而和5种公式计算的参考作物腾发量的回归系数为0.47～0.60，以蒸发皿水面蒸发量计算温室内的作物蒸腾量要优于以参考作物腾发量计算作物蒸腾量的方法。温室内香蕉树的蒸腾量和20 cm蒸发皿蒸发量线性相关，可以此计算温室内作物的蒸腾量。     

Estimation of turnover and equilibrium of soil organic matter using a mathematical approach

The methods based on N uptake of aerial-plants, soil organic matter （SOM） dynamics, Jenny＇s equation, and actual measurement of long-term field experiments in Jiaxing, Quzhou, Huangyan and Hangzhou of Zhejiang Province, China were used to determine the organic mineralization rate being helpful in estimating the organic requirement for SOM equilibrium. The results showed that the estimated mineralization ratios of SOM for Jiaxing and Quzhou were, respectively, 0.0404 and 0.0508 based on N uptake of aerial-plants in non-fertilized plots; 0.0405 and 0.012 using SOM dynamics in non-fertilized plots; and 0.0413 and 0.0513 using the actual investigated data and Jenny＇s equation. With Jenny＇s equation, soil organic C balance in manure ＋ N-P-K plots was estimated at nearly 28.8 g kg^-1 for Jiaxing and 32.4 g kg^-1 for Quzhou with predicted SOM linearly related to the actual investigated values （r^2 = 0.9640 for Jiaxing and 0.8541 for Quzhou）. To maintain the SOM balance in the non-fertilized plots the recommended rate of organic materials was 3 000-6 600 kg ha^-1, and the relevant rates of farm yard manure （FYM） in the manure and N-P-K plots were estimated at 3 375 （dry） and 17670 kg ha^-1 （wet） for Jiaxing, 1845 （dry） and 6090 kg ha^-1 （wet） for Quzhou.