The effects of Fe deficiency on low molecular weight organic acid exudation and cadmium uptake by Solanum nigrum L.

Abstract

The influence of Fe-deficiency on the root exudation of low molecular weight organic acids (LMWOAs), pH alteration and cadmium (Cd) accumulation and translocation were investigated in morel (Solanum nigrum L.) in hydroponic culture experiments. Tartaric, citric, malic and acetic acids were monitored because these acids were abundant and often detected as root exudates. Results showed that Fe-deficient plants excreted large amounts of LMWOAs in comparison with Fe-sufficient plants across all Cd treatments (p <0.05). In both cases the concentrations of the four organic acids were tartaric > citric > malic > acetic. The results showed that the Fe-deficient plants with higher concentrations of LMWOAs accumulated more Cd (p <0.05) and induced a decrease in solution pH compared with the Fe-sufficient plants. Cadmium accumulation in the Fe-deficient and Fe-sufficient plants had significant positive correlations with the exudation of malic and acetic acids (p <0.05 and p<0.01). Cadmium accumulation in the Fe-sufficient plants had a significant (p<0.01) positive correlation with the exudation of tartaric acid, whereas there was a negative correlation (p<0.01) between Cd accumulation and the exudation of tartaric acid in the Fe-deficient plants. No significant correlation between the exudation of citric acid and Cd accumulation was obtained. Our results indicate that Fe-deficiency could induce Cd accumulation and translocation through an increase of LMWOAs exudation and pH alteration, both of which enhance Cd bioavailability.     

Effect of difference between day and night temperature on tomato (Lycopersicon esculentum Mill.) root activity and low molecular weight organic acid secretion

The difference between day and night temperature (DIF) is a major environmental factor affecting crop growth, but the mechanisms are not fully understood. We investigated crop performance, root activity and concentrations of low molecular weight organic acids (LMWOAs) secreted by tomato (Lycopersicon esculentum Mill.) root under different DIF conditions. A fixed daily temperature of 25°C and five DIF treatments (?12, ?6, 0, 6 and 12°C) were used to grow tomato in a climate chamber. Root/shoot ratio; leaf maximum photosynthetic rate (P_max); root activity; total nitrogen (N), phosphorus (P) and potassium (K) concentrations in roots; and types and concentrations of LMWOAs were measured at different growth stages. Results showed that positive and negative DIFs inhibited the dry matter accumulation of aerial parts, while 0°C DIF was conducive to the accumulation. Compared to 0°C DIF, positive DIFs significantly increased root dry weight, P_max, root activity and total N, P and K concentrations in roots, while negative DIFs had contrary effects. During the whole growth period, tomato root activity decreased in the order of fruit setting stage, mature stage and flowering stage. Tomato roots secreted oxalic acid, formic acid, malic acid, malonic acid, lactic acid, acetic acid, citric acid, succinic acid and propionic acid under positive DIFs, while acetic acid was not detected in the negative DIF treatments. Oxalic acid concentration was significantly higher than other LMWOAs. Furthermore, in the same growth stage, positive DIFs caused more LMWOA secretion than negative DIFs and 0°C DIF. There were significant positive correlations between the total LMWOA concentration and root activity, root/shoot ratio, P_max and total N, P and K concentrations in roots. Based on the results, more attention should be paid to the potential effect on tomato growth posed by DIFs, positive DIFs have higher positive influence than negative DIFs, and 6°C DIF is best for greenhouse tomato growth.     

不同镉积累类型小麦根际土壤低分子量有机酸与镉的生物积累

采用土壤培养方法研究低镉积累小麦烟 86103和高镉积累小麦莱州 953不同生育期土壤低分子量有机酸含量与组成 ,及其与镉生物积累的关系。结果表明 ,不同镉积累类型小麦在高镉土壤中其根系镉含量差异不显著 ,但地上部镉浓度烟 86103显著低于莱州 953,而在低镉土壤中根系和地上部镉浓度烟 86 10 3均显著低于莱州 95 3。根际土壤有机酸 (柠檬酸、酒石酸、乙酸和丙酸 )含量及有机酸总量均为低镉品种烟 86103显著低于高镉品种莱州953。两个品种不同生育期有机酸含量均表现为柠檬酸 酒石酸 丙酸 乙酸 ,且各有机酸含量占有机酸总量的百分数表现稳定。小麦镉的生物积累与有机酸种类没有特异性关系 ,但与有机酸的总量有关。根际不同有机酸的水平对于土壤镉的复合或螯合溶解 ,在引起两品种地上部镉生物积累的差异方面起重要作用。     

氮素对不同大豆品种根系分泌物中有机酸的影响

采用室内溶液培养方法,分别研究了接种根瘤菌处理下,两种氮源和两种氮浓度对两个大豆品种根系分泌物中有机酸的影响。结果表明,合丰25号根系分泌的有机酸种类和数量无论苗期或花期,接种或不接种根瘤菌,均表现为硝态氮处理高于酰胺态氮处理,表明合丰25号大豆更喜硝态氮,硝态氮促进了有机酸的分泌。绥农10号在酰胺态氮下的有机酸种类和数量均高于硝态氮处理,表明其更喜酰胺态氮,酰胺态氮下根瘤菌的存在增加其根系分泌物中有机酸种类和数量。可见,大豆根系分泌物中有机酸的种类和数量因品种而异,因品种对氮源的喜好而变化;根瘤菌在不同程度上增强或减弱根系有机酸的分泌作用。柠檬酸受氮素供应浓度影响很大,当氮素供应浓度较低时,大豆根系分泌物中可检测到柠檬酸,供氮浓度升高则检测不到。     

Biochars immobilize soil cadmium, but do not improve growth of emergent wetland species Juncus subsecundus in cadmium-contaminated soil

Purpose

An addition of biochar mixed into the substrate of constructed wetlands may alleviate toxicity of metals such as cadmium (Cd) to emergent wetland plants, leading to a better performance in terms of pollutant removal from wastewater. The objective of this study was to investigate the impact of biochars on soil Cd immobilization and phytoavailability, growth of plants, and Cd concentration, accumulation, and translocation in plant tissues in Cd-contaminated soils under waterlogged conditions.

Materials and methods

A glasshouse experiment was conducted to investigate the effect of biochars derived from different organic sources (pyrolysis of oil mallee plants or wheat chaff at 550 °C) with varied application amounts (0, 0.5, and 5 % w/w) on mitigating Cd (0, 10, and 50 mg kg^?1) toxicity to Juncus subsecundus under waterlogged soil condition. Soil pH and CaCl₂/EDTA-extractable soil Cd were determined before and after plant growth. Plant shoot number and height were monitored during the experiment. The total root length and dry weight of aboveground and belowground tissues were recorded. The concentration of Cd in plant tissues was determined.

Results and discussion

After 3 weeks of soil incubation, pH increased and CaCl₂-extractable Cd decreased significantly with biochar additions. After 9 weeks of plant growth, biochar additions significantly increased soil pH and electrical conductivity and reduced CaCl₂-extractable Cd. EDTA-extractable soil Cd significantly decreased with biochar additions (except for oil mallee biochar at the low application rate) in the high-Cd treatment, but not in the low-Cd treatment. Growth and biomass significantly decreased with Cd additions, and biochar additions did not significantly improve plant growth regardless of biochar type or application rate. The concentration, accumulation, and translocation of Cd in plants were significantly influenced by the interaction of Cd and biochar treatments. The addition of biochars reduced Cd accumulation, but less so Cd translocation in plants, at least in the low-Cd-contaminated soils.

Conclusions

Biochars immobilized soil Cd, but did not improve growth of the emergent wetland plant species at the early growth stage, probably due to the interaction between biochars and waterlogged environment. Further study is needed to elucidate the underlying mechanisms.     

添加有机酸对土壤镉形态转化及苋菜镉积累的影响

植物根系分泌的低分子量有机酸能够与土壤中的镉形成镉–有机酸复合体,从而影响根际镉的移动性。本文通过添加有机酸对土壤镉形态转化的研究,阐明有机酸与镉生物积累的关系。采用盆栽试验及土壤培养等方法,研究了添加苹果酸、柠檬酸对赤红壤和黄棕壤中镉的形态转化以及超积累型苋菜天星米镉生物积累的影响。结果表明,与Cd 25 mg/kg处理比较,Cd 25 mg/kg＋苹果酸、Cd 25mg/kg＋柠檬酸处理对苋菜生物量未产生影响,但显著增加苋菜根系及地上部镉含量;添加苹果酸、柠檬酸处理显著降低土壤专性吸附态Cd含量,却显著增加了交换态Cd、碳酸盐结合态Cd和有机结合态Cd含量。说明添加苹果酸、柠檬酸还能够通过影响土壤镉形态转化而促进苋菜对镉的积累。     

Quantitative analysis of soluble exudates produced by ectomycorrhizal roots as a response to ambient and elevated CO2

Despite its potential impact on soil carbon flow, few studies have attempted to quantify the effects of elevated carbon dioxide (CO₂) on production of exudates by mycorrhizal plants. In this study we quantified low molecular weight (LMW) organic compounds exuded by non-mycorrhizal (NM) and ectomycorrhizal (ECM) plants in relation to exposure to elevated CO₂. Scots pine seedlings, either colonized by one of eight different ECM fungi or non-mycorrhizal (NM), were exposed to either ambient (350 ppm) or elevated (700 ppm) concentrations of CO₂. Exudation of LMW organic acids (LMWOAs), amino acids, dissolved monosaccharides and total dissolved organic carbon (DOC) was determined and exudation rates were calculated per g root and fungal dry mass. CO₂ had a significant impact on exudation. Under elevated CO₂, exudation of total LMWOAs increased by 120-160%, amino acids by 250%, dissolved monosaccharides by 130-270% and DOC by 180-220% compared to ambient CO₂ treatment. Net CO₂ assimilation rates increased significantly by 41-47% for seedlings exposed to elevated CO₂. Exuded C calculated as a percentage of assimilated CO₂ increased by 41-88% in the elevated CO₂ treatment compared to ambient CO₂ treatment.     

镉积累差异水稻品种生长发育对清除NO的响应

  【目的】   研究一氧化氮 (NO) 对镉 (Cd) 胁迫下水稻苗期生理生化及氮代谢响应的调节作用,探讨通过清除NO提高水稻耐Cd能力的措施。   【方法】   以Cd高积累 (TN1) 和Cd低积累 (春江06) 品种为材料,进行了Cd胁迫 (40 μmol/L) 水培试验。以Cd胁迫营养液为对照,在对照基础上设置添加硝普钠 (Cd+SNP)、添加NO清除剂CPTIO (Cd+CPTIO)、添加硝酸还原酶抑制剂钨酸钠 (Cd+TU) 处理,共4个处理。处理后12天,测定不同处理对水稻幼苗生长、NO₃–-N分配、根系特性及光合特性的影响。   【结果】   NO对高Cd和低Cd积累水稻品种的影响不同。与对照相比,Cd+SNP处理降低高Cd积累水稻品种幼苗地上部和地下部NO₃?-N含量,但对幼苗生物量和氮素吸收没有显著抑制效果;Cd+CPTIO处理会提高幼苗生长、氮素积累量及氮效率 (P < 0.05);增加或清除NO处理均显著降低了地上部和地下部的Cd含量。对于低Cd积累水稻品种,Cd+SNP、Cd+CPTIO、Cd+TU处理间幼苗生物量、氮素吸收量均无显著差异。   【结论】   品种基因型对NO信号的调节敏感度不同,高Cd 积累品种清除NO处理可以显著抑制Cd的吸收和向地上部的运转,促进幼苗的生长和对氮素的吸收利用,抑制硝酸还原酶活性处理缓解Cd胁迫促进幼苗生长的效果不稳定。而对于低Cd积累水稻品种,清除NO处理也有一定的缓解Cd吸收和向地上运转的效果,但其重要性不如基因本身的拒Cd能力。因此,Cd胁迫下,高Cd积累水稻品种采用清除NO的措施可有效缓解Cd胁迫,促进水稻的生长,但对于低Cd积累水稻品种,清除NO也可以进一步降低Cd的向上运输,但是对水稻幼苗生长和氮素利用的影响不显著。     

Bioavailability and Rhizotoxicity of Cd to Pea (Pisum sativum L.)

Risk assessment of cadmium (Cd) contamination in soils requires identifying the bioavailable portion of the total Cd, a portion that is determined by environmental conditions such as pH and calcium (Ca) level in soils and by the physiological processes going on in the plant roots. Growth tests in solutions were conducted to develop a terrestrial biotic ligand model to describe uptake and rhizotoxicity of Cd to pea (Pisum sativum L. cv. Lincoln). Inhibition concentration associated with a 50% reduction in root elongation (IC₅₀) values were found to vary with external Ca²⁺ and H⁺ activities. Root-bound Ca was found to reach a plateau of about 63 µmol g^?1 (dry weight) although Ca treatment increased from 0.04 to 2 mmol L^?1. When experimental treatments (e.g., pH 6, Ca 0.2 to 2 mM) resulted in sufficient Ca supply, dose–response curves relating root elongation to root-bound Cd could be modeled with Weibull equations; IC₅₀ values were expressed in terms of root-bound Cd concentration. When the treatments (e.g., pH 4 or 5, Ca 0.04 mM) suggested a low Ca supply, root elongation was more sensitive to Ca content and root-bound Ca concentration became the dominant predictor variable. Cd accumulation was modeled by treating the pea roots as an assemblage of biotic ligands with known site densities (Q _Lj ) and proton binding constants (K _HLj ). The logK _Ca and logK _Cd values were established using measured root-bound ion concentrations and solution chemistry. The logK _Ca values were negatively correlated to root Ca contents. The logK _Cd values were positively correlated to logK _Ca values. Explanations for the changing of constants are discussed.     

Investigation of the changes in low molecular weight organic acids and other physiological parameters by nitric oxide application in two wheat cultivars exposed to boron stress

Boron (B) is one of the essential nutrients for the growth of plants, but its high concentrations are toxic for plants. Thus, B toxicity is a big challenge in crop cultivation. Nitric oxide (NO) is a small signaling molecule that has cytoprotective roles in plants. We investigated whether exogenous sodium nitroprusside (SNP), which is a NO donor, may succeed to alleviate B-induced toxicity in wheat cultivars. Seedlings were grown for 10 days in a growth chamber at 25°C with 16 hr light–8 hr dark photo cycle. After high B application, the effects of SNP on growth parameters; electrolyte leakage (EL); changes in reactive oxygen species [contents of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and proline]; the activities of antioxidant enzymes [glutathione peroxidase (GSHPx), glutathione reductase (GR), and glutathione S-transferase (GST)] and nitrate reductase (NR); and low molecular weight organic acid (LMWOAs) contents and also chlorophyll and total carotenoid contents were investigated in both shoots and roots of two different wheat cultivars. All experiments were carried out in triplicate. 0.2 mM SNP application ameliorated the chlorophyll and total carotenoid contents, and growth parameters such as shoot length, root length, and fresh weight in both wheat cultivars exposed to B stress. SNP reduced the B-induced lipid peroxidation, EL, and proline and H₂O₂ content in wheat cultivars. SNP application also increased the activities of NR and antioxidant enzymes, including GSHPx, GR, and GST in wheat cultivars exposed to B toxicity. All of the tested LMWOAs including succinic, propionic, butyric, oxalic, formic, malic, malonic, and benzoic acids were increased by SNP treatment in the shoots and roots of both wheat cultivars exposed to B toxicity. In conclusion, results obtained from this study have demonstrated that interactive effects of SNP with B considerably reduced the toxic effects of B in wheat cultivars.     

Equilibrating stable Cd isotopes with acidic soils

ABSTRACT

Cadmium (Cd) in the soil solution is in dynamic equilibrium with the reservoir of bioavailable Cd attached to the solid phase, i.e. the labile pool (Cd_E). Traditionally, Cd_E is estimated using the radioisotope ¹⁰⁹Cd, which has severely restricted access to estimates of Cd_E. Using stable isotope dilution and isotope ratio measurement by inductive coupled plasma-quadrupole mass spectroscopy (ICP-QMS) would increase access to estimates of Cd_E; however, detail remains scant about the optimal conditions for equilibration and measurement. We report optimal conditions for spiking with ¹¹⁰Cd, batch equilibration and ICP-QMS measurement of the ratio of ¹¹⁰Cd to ¹¹¹Cd using results for six acidic soils with total Cd concentrations of 0.19–6.4 mg Cd kg^?1, suspended in three background electrolytes (10 mM CaCl₂, 1 M NH₄NO₃, and 1 M NH₄Cl). Our optimised procedure produces robust estimates of Cd_E. Application of this approach will greatly increase access to estimates of Cd_E and to the investigation of its role in Cd uptake by plants.     

Cadmium accumulation and partitioning in Ocimum basilicum as influenced by the application of various potassium fertilizers

Potassium (K) is one of the major essential nutrient elements whose application of organic or nano-chelate-fertilizers has received increased attention recently. Cadmium (Cd) contamination in agricultural soils and environment is increasing due to the over-application of Cd-containing phosphate fertilizers. But few studies have been carried out on the environmental influences of K-nano-chelate fertilizers especially on Cd-polluted soils. Therefore, the effects of K-fertilizer application in different rates (0, 100 and 200 mg kg^?1 soil) and forms (KCl, K₂SO₄ and K-nano-chelate) on Cd content and partitioning in Ocimum basilicum grown on an artificially Cd-contaminated calcareous soil (with 40 mg Cd kg^?1 soil) were studied under greenhouse conditions. Cadmium decreased shoot dry weight (SDW), but did not affect root dry weight (RDW) and no consistent trend was observed with applied K. Cadmium increased shoot and root Cd concentration or uptake. KCl and K₂SO₄ increased shoot Cd concentration compared to that of control, whereas K-nano-chelate did not affect it. In Cd-treated soils the mean value of Cd translocation factor (ratio of Cd concentration in shoots to that of roots) decreased by 60% as compared to that of the control. Application of 100 mg K-K₂SO₄ and 100 and 200 mg K-nano-chelate increased the Cd translocation factor by 49, 59 and 112% in Cd-treated soils, respectively. In Cd-treated soils, greater amounts of Cd accumulated in roots. K-nano-chelate could mitigate the adverse effect of Cd on SDW and Cd accumulation in plants grown on Cd-polluted soils, so the risk of Cd entrance to the food chain is reduced (however, in Cd-untreated soils, K-nano-chelate increased the Cd translocation factor higher than other K sources). In Cd-polluted soils KCl was the most inappropriate fertilizer that may intensify Cd accumulation in plants. However, it may be useful in the phytoremediation of Cd-polluted soils.     

Intercropping of Sonchus asper and Vicia faba affects plant cadmium accumulation and root responses

The cadmium (Cd) pollution of farmland soil is serious in the world. The present study investigated the effects of intercropping Vicia faba and the hyperaccumulator Sonchus asper on the Cd accumulation and root responses (morphology and secreted organic acids) of plants grown on soil from a mining area in Yunnan Province, China, under different Cd stress levels (0, 50, 100, and 200 mg kg^-1). Intercropping increased the biomass of both S. asper and V. faba, as well as the Cd accumulation and Cd transfer coefficient from roots to shoots of S. asper, but decreased those of V. faba in the 200 mg kg^-1 Cd treatment. The Cd concentrations in roots, shoots, and grains from intercropped V. faba plants were positively correlated (P<0.05) with the N,N-diethyl phenylacetamide-extractable Cd content in soil. In the 50 mg kg^-1 Cd treatment, intercropping decreased citric and malic acids in root secretions of S. asper. Intercropped V. faba secreted more citric, oxalic, acetic, and malic acid compared with S. asper. Intercropping also increased root length and root surface area of both S. asper and V. faba. At 50 mg kg^-1 Cd, root length for S. asper was higher than that at 0 mg kg^-1 Cd, whereas V. faba roots had significantly decreased length and mean diameter. Intercropping of S. asper and V. faba is suggested as an in situ phytoremediation strategy of Cd-contaminated soils and may improve the food quality of V. faba.     

Effects of Graphene Oxide and/or Cd<Superscript>2+</Superscript> on Seed Germination,Seedling Growth,and Uptake to Cd<Superscript>2+</Superscript> in Solution Culture

With increasing graphene oxide (GO) applications in industry and biomedicine, effects of GO on microorganisms, animals, and human health have been frequently studied; however, direct and indirect effects of GO on plants are seldom concerned. In this study, effects of GO and/or Cd²⁺ on seed germination, seedling growth, and uptake to Cd²⁺ were investigated in solution culture. The results showed that GO could quickly adsorb Cd²⁺ in solution, and the higher the GO concentration was, the lower the residual Cd²⁺ concentration was in solution. Rice seed germination, seminal root length, and bud length decreased with increasing GO and Cd²⁺ concentrations respectively, while the presence of GO could alleviate the inhibitive effects of Cd²⁺ on seminal root and bud growth compared with the single Cd²⁺ treatment. In maize seedling, fresh weights of shoot and root showed similar responses to the presence of Cd²⁺ and/or GO. Compared with the single Cd²⁺ treatment, root Cd concentrations were generally increased by GO in high Cd²⁺ solution (20 mg/L), while were slightly affected by GO in low Cd²⁺ solution (5 mg/L) independent of GO concentrations except for 100 mg/L GO. Shoot Cd concentrations were decreased by low GO (100 mg/L) while were increased by high GO (>?500 mg/L) independent of Cd²⁺ concentrations in solution. Moreover, significant interactive effects of GO and Cd²⁺ on root and shoot Cd concentrations were observed. This study indicates that GO can change the effects of Cd²⁺ on seed germination, seedling growth, and uptake to Cd²⁺ in solution through its adsorption on Cd²⁺.     

Low molecular weight organic acids released from roots of durum wheat and flax into sterile nutrient solutions

Knowledge of the composition and quantity of organic substances released from roots of different plant species is necessary for understanding the chemical and biological processes in the rhizosphere. The present study was undertaken to quantify low molecular weight organic acids (LMWOAs) released from roots of five cultivars/lines of durum wheat (Triticum turgidum var. durum L.): Kyle, Sceptre, DT618, DT627, and DT637 and four cultivars/ lines of flax (Linum usitatissiumum L.): Somme, Flanders, AC Emerson, and YSED 2. Plants were grown in sterile nutrient solution cultures and amounts of organic acids exuded by roots were analyzed by gas chromatography. The LMWOAs varied significantly among both durum wheat and flax cultivars and oxalic, malonic, fumaric, succinic, acetic, malic, citric and tartaric acids were detected in root exudates of both species. Generally, oxalic and acetic acids were predominant in durum wheat exudates and oxalic, acetic and malic acids were predominant in flax root exudates. High oxalic acid concentrations occurred in root exudates of durum wheat cultivars DT627 and DT637, and flax cultivar YSED 2. Compared with the other durum wheat cultivars, Kyle released the lowest total amount of LMWOAs, whereas among the flax cultivars, YSED 2 had the highest total amount of acids secreted from roots. The data showed that the release of LMWOAs from roots was cultivar dependent. The results provide valuable background information for studying the role of root exudates in soil‐plant relationships.     

ROOT GROWTH OF UPLAND RICE GENOTYPES AS INFLUENCED BY NITROGEN FERTILIZATION

The plant root system is an important organ which supplies water and nutrients to growing plants. Information is limited on influence of nitrogen fertilization on upland rice root growth. A greenhouse experiment was conducted to evaluate influence of nitrogen (N) fertilization on growth of root system of 20 upland rice genotypes. The N rate used was 0 mg kg^?1(low) and 300 mg kg^?1(high) of soil. Nitrogen X genotype interactions for root length and root dry weight were highly significant (P < 0.01), indicating that differences among genotypes were not consistent at two N rates. Overall, greater root length, root dry weight and tops-roots ration were obtained at an N fertilization rate of 300 mg kg^?1compared with the 0 mg N kg^?1soil. However, genotypes differ significantly in root length, root dry weight and top-root ratio. Nitrogen fertilization produced fine roots and more root hairs compared with absence of N fertilizer treatment. Based on root dry weight efficiency index (RDWEI) for N use efficiency, 70% genotypes were classified as efficient, 15% were classified as moderately efficient and 15% were classified as inefficient. Root dry weight efficiency index trait can be incorporated in upland rice for improving water and nutrient efficiency in favor of higher yields.     

Effect of liming using a partial mixing technique on reductions in the seed cadmium levels for soybeans (Glycine max (L.) Merr.) under field conditions

To reduce the availability of soil cadmium (Cd) to soybeans (Glycine max (L.) Merr.), we employed a liming by partial mixing (PM) technique in two drained paddy fields on Gray Lowland soils, which had 0.1 mol L^–1 hydrochloric acid-extractable Cd concentrations as high as 1.08 and 1.40 mg kg^–1. Among the different application methods tested, PM application (PM2) using a width of 20 cm and a depth of 20 cm was found to be most appropriate for reducing the seed Cd concentration and to obtain the optimum yield at Site A. Under PM2, a liming rate of 38% of that for broadcast incorporated into the surface 15 cm layer (Bc) was suitable to reduce the seed Cd concentration at Site A, whereas the lime rate with PM2 was set at 50% of that for Bc (PM2-50) at Site B due to the higher availability of soil Cd. The root system was limited within the range of lime and fertilizer application for PM2 as well as PM2-50; thus, the lime and fertilizer were supplied successfully to the rooting zone. The soil pH value was lower under PM2 at Site A and PM2-50 at Site B compared with Bc, whereas the seed Cd concentration was lower for PM2 and PM2-50. This may be explained by the intensive uptake of calcium and magnesium with PM2 as well as PM2-50. The seed Cd concentration in the cultivar “Ryuhou” at the target pH of 6.5 was approximately 30% lower with PM2-50 than Bc at Site B. In addition, the average seed Cd concentrations in one cultivar and two lines, characterized by the lower Cd uptake with higher retention in roots and higher accumulation in leaves, were approximately 40% lower compared with “Ryuhou.” Thus, the combination of liming with PM2-50 at the target pH of 6.5 and a low-Cd cultivar (or lines) minimized the seed Cd concentration. The highest seed Cd concentration was found in the first year of soybean cultivation, which was considered to be caused by the release of Cd from organic nitrogen compounds during the nitrogen mineralization process.     

Dry Matter and Nitrogen Accumulation and Root Morphological Characteristics of Two Clonal Selections of ‘Russet Norkotah’ Potato as Affected by Nitrogen Fertilization

New clonal selections with increased vine vigor and stress resistance have been identified for the potato cultivar ‘Russet Norkotah’. However, the importance of clonal variation in nitrogen (N) uptake and root morphological properties is not well known. The objective of this study was to determine the effect of N fertilization on dry matter and N accumulation and root morphological parameters of two clonal selections of ‘Russet Norkotah’. A field experiment was conducted in 2002 using the standard ‘Russet Norkotah’ clone (SRC) and Texas selection 112 (TX112) of ‘Russet Norkotah’, grown at 0 and 150 kg N ha^{? 1}. Whole plants were excavated at 54, 76, and 96 days after planting; partitioned into tubers, vines, roots, stolons, and fruits; and their dry matter and N accumulation were determined. Soil cores were obtained from 10 spatial locations relative to the plant, and used for determination of root length (RL), root length density (RLD), root average diameter (RAD), and root dry weight (RDW). Soil inorganic N content was also measured. Nitrogen fertilization increased tuber yield and dry matter and N accumulation. Fertilizer N application did not affect RL, RLD, or RDW, but resulted in a larger proportion of roots close to the top of the potato hill. Tuber yield and dry matter and N accumulation were similar for the two clonal selections. The TX112 clone, however, partitioned more dry matter and N to vines and less dry matter and N to tubers compared with the SRC clone. Soil nitrate concentration was significantly higher for SCR than for the TX112 clone in the fertilized treatment at 54 DAP, and was low and similar between clones thereafter. Root length and RLD were significantly higher for the TX112 clone compared with SRC, and both clones had a similar spatial distribution of roots. Under the conditions of this study where moisture and disease stress were limited and under a short growing season, the larger root system and increased vine vigor of the TX112 clone did not provide any advantage in terms of plant production as either dry-matter accumulation or tuber yield.     

Persistence of CaCl2 washing effect for amelioration of a Cd-contaminated paddy field soil

Abstract

Soil washing is one of the methods used to remediate soil contaminated with heavy metals, and when the contaminated elements have been effectively removed the washed soil can be used for agriculture. Soil washing was conducted using 0.5 mol L^?1 CaCl₂ solution at pH 4 as an extracting agent to remediate a paddy field soil contaminated with Cd. Dolomite powder was applied to neutralize the soil to the original pH 6.2. After CaCl₂ washing, the content of Cd extractable in 0.1 mol L^?1 HCl decreased from 2.4 to 0.8 mg kg^?1. Subsequently, a pot experiment was carried out to evaluate the effect of soil washing on Cd concentration in polished rice (Cd_pr) for three successive years. Using the washed soil, Cd_pr was ≤ 0.2 mg kg^?1 with and without a treatment that simulates midseason drainage, whereas it was > 0.5 mg kg^?1 in the unwashed soil with the midseason drainage treatment. The reasons for low Cd_pr growth in the washed soil were the low content of exchangeable Cd in the soil and the resultant high soil pH (> 7). To evaluate the effect of soil pH on Cd_pr in the fourth year, we adjusted soil pH to 5 with H₂SO₄ before transplanting rice seedlings. The Cd_pr in the washed soil with the midseason drainage treatment increased to 0.47 mg kg^?1, whereas it was less than 0.2 mg kg^?1 under continuous flooding. Thus, high pH or whole season flooding are important to keep Cd_pr at ≤ 0.2 mg kg^?1 even after soil washing. With the application of dolomite and other ordinary fertilizers, soil properties were little affected by the present soil washing procedure because the difference in rice yield between the washed and unwashed plots was not significant within each year.     

低分子有机酸对土壤中重金属的解吸及影响因素

研究了柠檬酸、草酸、酒石酸和苹果酸对矿区土壤中重金属Pb、Cd、Cu和Zn的解吸行为,并探讨了介质pH值对其解吸土中重金属的影响。振荡解吸试验结果表明四种低分子有机酸对供试污染土壤中Pb、Cd、Cu和Zn都具有一定的解吸能力。由于土壤中重金属有效态含量较低,各重金属的解吸率都不高。在对Pb和Cd的解吸中,各低分子有机酸能力大小顺序为柠檬酸>酒石酸≈苹果酸>草酸;Cu的解吸顺序为柠檬酸>草酸>酒石酸≈苹果酸;Zn的解吸顺序为酒石酸>柠檬酸≈苹果酸>草酸。低分子有机酸随浓度的增加,其解吸能力提高。低分子有机酸对重金属的解吸量随pH值的降低而增加。