Physiological Disorder of Rice Associated with High Levels of Iron in Growth Medium

Three rice (Oryza sativa L.) varieties viz. ‘CR 683‘, ‘Budumoni’ “Budumoni”, and ‘Akisali’ were grown in sand culture in a greenhouse with three levels of iron (Fe) in nutrient solutions viz., 0.045 (control), 5.34, and 7.12 mM Fe to study the effects of iron on physiology of rice seedling growth. Shoot length, root, and shoot dry weights were reduced significantly by higher levels of Fe in the medium. Results of leaf bronzing have revealed higher bronzing score in the seedlings grown at 7.12 mM Fe in the growth medium. Occurrence of bronzing was severe in varieties ‘CR683’ and ‘Akisali’. Variety ‘Budumoni'maintained higher leaf chlorophyll content, nitrate reductase activity and total soluble protein in the leaves at 5.34 and 7.12 mM Fe. Higher concentration of iron in the nutrient medium exerted an inhibiting effect on the concentration and content of almost all the macro and micronutrients in the root and shoot. Higher Fe and nitrogen (N) contents and lower phosphorus (P), potassium (K), manganese (Mn), copper (Cu), and zinc (Zn) were determined in roots and shoots in plants grown in medium supplied with 7.12 mM Fe. The variety ‘Budumoni’ “Budumoni” performed relatively better in comparison to other tested varieties at 7.12 mM Fe in the growth medium. ‘Budumoni’ “Budumoni” can be considered a suitable rice variety to use in the rice-breeding programme for Fe toxicity tolerance in acid soils of Assam.     

Ratios of Nutrients in Lowland Rice Grown on Two Iron Toxic Soils in Nigeria

ABSTRACT

Iron (Fe) toxicity is a widespread nutritional soil constraint affecting rice production in the wetland soils of West Africa. Critical levels of total iron in plant causing toxicity is difficult to determine as different rice cultivars respond to excessive Fe^{2 +} in various ways in what is called “bronzing” or “yellowing” symptoms (VBS). An investigation was conducted to evaluate the relationship between plant growth and nutrient ratios at four iron levels (1000, 3000, 4000 μ g L^?1) and control. This involved two rice cultivars (‘ITA 212’ and ‘Suakoko 8’), and two soil types (Aeric Fluvaquent and Aeric Tropaquept). The experimental design was a 2 × 2 × 4 factorial in a completely randomized fashion with four replications. The results showed that nutrient ratios [phosphorus (P)/Fe, potassium (K)/Fe, calcium (Ca)/Fe, magnesium (Mg)/Fe, and manganese (Mn)/Fe), Fe content, and Fe uptake vary widely with the iron levels as well as with the age of the cultivars. The iron toxicity scores expressed as VBS increased with increasing Fe^{2 +} in the soils, resulting in simultaneous reduction of the following variables: plant height, tiller numbers/pot, relationships grain yield (GY) and dry matter yield (DMY). There were no significant difference between nutrient ratios, Fe contents, Fe uptake, the GY and DMY of both rice cultivars on both soil types. Multiple stepwise regression analysis showed that Fe uptake and Fe contents contributed 42% and 17% respectively to the variation in the grain yield of ‘ITA 212’ on Aeric Tropaquept. On both soil types and cultivars, Fe uptake and Fe content contributed between 26 and 68% to the variation in the DMY, while the nutrient ratios (P/Fe, K/Fe, Ca/Fe, and Mn/Fe) contributed between 3% and 13% DMY. Thus, it could be concluded that iron toxicity in rice is more a function of a single nutrient (Fe) rather than nutrient ratios.     

Classification of rice genotypes based on their mechanisms of adaptation to iron toxicity

Iron (Fe) toxicity is a nutritional disorder that affects lowland rice (Oryza sativa L.). The occurrence of excessive amounts of reduced Fe(II) in the soil solution, its uptake by the rice roots, and its transpiration‐driven transport result in elevated Fe(II) concentrations in leaf cells that catalyze the formation of reactive oxygen species. The oxidative stress causes rusty brown spots on leaves (bronzing) and the reduction of biomass and yield. While the use of resistant genotypes is the most promising approach to address the problem, the stress appears to differentially affect rice plants as a function of plant age, climatic conditions, stress intensity and duration, and the prevailing adaptation mechanism. We comparatively assessed 21 contrasting 6‐week‐old rice genotypes regarding their response (symptom score, biomass, Fe concentrations and uptake) to a 6 d iron pulse of 1500 mg L^–1 Fe(II). Eight selected genotypes were further compared at different stress intensities (0, 500, 1000, and 1500 mg L^–1 Fe(II)) and at different developmental stages (4‐, 6‐, and 8‐week‐old plants). Based on Fe‐induced biomass reduction and leaf‐bronzing score, the tested spectrum was grouped in resistant and sensitive genotypes. Linking bronzing scores to leaf iron concentrations allowed further differentiation into includer and excluder types. Iron precipitation on roots and organ‐specific iron partitioning permitted to classify the adaptation strategies into root exclusion, stem and leaf sheath retention, and leaf blade tissue tolerance. The effectiveness of these strategies differed with stress intensity and developmental stage. The reported findings improve the understanding of Fe‐stress response and provide a basis for future genotype selection or breeding for enhancing Fe‐toxicity resistance in rice.     

Toxic concentrations of iron and manganese in leaves of Phaseolus vulgaris L. growing on freely‐drained soils of pH 6.5 in Northern Tanzania

Abstract

A bronzing symptom of trifoliolate leaves of Phaseolus vulgaris is described which has been found to be widespread on the southern slopes of the Meru and Kilimanjaro massifs in northern Tanzania. The symptom occurred on plants growing on freely draining soils of moderate pH and has led to complete loss of yield of badly affected plants. Leaves with the bronzing symptom contained large concentrations of iron (>3080 mg/kg) and manganese (>760 mg/kg) considered to be toxic in Phaseolus plants.     

Contribution of iron associated with high-molecular-weight substances to the maintenance of the SPAD value of young leaves of barley under iron-deficient conditions

Abstract

In higher plants, it is well known that the retranslocation of iron from old leaves to young leaves is difficult; as a result, iron deficiency leads to interveinal chlorosis, particularly in the young leaves. However, in the case of barley, young chlorotic leaves can grow under conditions of long-term iron deficiency. Previously, we have reported that the distribution and retranslocation characteristics of iron in barley may be better adapted to iron deficiency than those in rice. Furthermore, barley maintained a relatively high chlorophyll index (SPAD value) even when its iron content was not higher than that of rice. In this study, we aimed to predict the chemical form of iron that contributes to the physiologically available iron in barley leaves. To examine the correlation between plant growth and the SPAD value with the amount of fractionated iron, we cultured plant materials in a culture solution containing various iron concentrations. We compared these correlations among barley, rice and sorghum and among three barley cultivars. To compensate for the amount of mugineic acid phytosiderophores (MAs) in the culture solution, we cultured different plant species in the same container. The results revealed that the amount of soluble iron associated with the high-molecular-weight substances (MW >10,000) correlated with the SPAD value of the young barley leaves and the R² value (determination coefficient) of barley was higher than the values of rice and sorghum.     

Effect of Plant Residue on Germination of Selected Rice Cultivars

Abstract

The effects of rice straw and alligator weed (Alternanthera philoxeroides) residue on germination of selected rice cultivars grown in Louisiana were studied. Germination was influenced by both plant residue source and application rate. Alligator weed, which caused a rapid decrease in soil redox and pH, had a greater impact on germination than rice straw addition. There were distinct differences in rice cultivars ‘response’ to plant residue application rate and source. Alligator weed showed significant germination inhibition for all cultivars tested as compared to rice straw.     

Italian ryegrass–rice rotation system for biomass production and cadmium removal from contaminated paddy fields

Purpose

Growing energy plants in Cd-contaminated soil to produce bioenergy feedstock and remove excess Cd in the soil is a promising approach to the production of sustainable bioenergy feedstock and safe food. Rice, an important staple food for human beings, is a major source of Cd intake in human beings. Italian ryegrass (Lolium multiflorum Lam) is a potential bioenergy plant with high biomass productivity and high biofuel conversion efficiency.

Materials and methods

An Italian ryegrass and rice crop rotation system would be beneficial for the harvest of bioenergy and phytoremediation. An Italian ryegrass–rice rotation system was established in a moderately Cd-contaminated paddy field. The yield of biomass, amount of Cd removal, and transfer factors for three cropping systems (winter fallow, non-cutting, and cutting) were evaluated over 3 consecutive years of field experiments.

Results and discussion

The total biomass production of the Italian ryegrass–rice rotation system was significantly higher than that of the traditional cropping system. Biomass growth was further promoted by cutting during March. No significant differences were found in yield or Cd concentration of brown rice among the different cropping systems. Total Cd accumulation in rice and Italian ryegrass straw in the rotation cropping system was significantly higher than that in the winter fallow cropping system. Cd was mainly accumulated in the roots, and the ability of Italian ryegrass to transport Cd to the leaves was higher than that of rice.

Conclusions

The Italian ryegrass–rice rotation system is a potential cropping system for Cd-contaminated paddy fields. The average annual yield of biomass was 1656.6 kg km^?2, and the average annual amount of Cd removal was more than 9.8 g Cd km^?2.

     

Control of arsenic toxicity in rice plants grown on an arsenic‐polluted paddy soil

Abstract

Paddy soils of over 500 hectares had been polluted by arsenic (As) from tailings at an abandoned lead‐zinc mine at Shaoxing, Zhejiang, China. Several field experiments were conducted to establish measures for reducing As toxicity to rice plants. The results obtained were as follows. Fresh Chinese milkvetch (Astragalus sinicus L.) was not supposed to be used as green manure in arsenic polluted paddy soils. Although liming (1,500 kg CaO hectare^‐1) could reduce water‐soluble As (H₂O‐As) in the soil, the rice plant grew badly. The treatments of FeCl₃ (25 mg Fe kg^‐1 soil) and MnO₂ (25 mg Mn kg^‐1 soil) could markedly lower the H₂O‐As and arsenite [As(III)] percentage in the soil and make the plant grow better than the control experiment (CK). Without adding any materials to the soil, wetting and drying (furrowing and draining) in the paddy soil could increase soil redox potential greatly and lower the H₂O‐As and As(III) percentage obviously leading to better rice growth. In addition, the As contents of roots, flag leaf, grain, and husked rice of 11 new cultivare of early rice were determined and correlation analysis was conducted. Uptake and accumulation of As in different parts of cultivars Zhefu‐802 and Erjiufeng at the 4 As levels of the paddy soil demonstrated that the As contents in husked rice of both cultivars exceeded the hygienic standard (0.7 mg As kg^‐1) when they grew in the paddy soil having total As content of about 70 mg kg^‐1 for Zhefu‐802 and 100 mg kg^‐1 for Erjiufeng, respectively.     

Toxic concentrations of iron and manganese in leaves of phaseolus vulgaris L. growing on freely‐drained soils of ph 6.5 in northern Tanzania

Abstract

A bronzing symptom of trifoliolate leaves of Phaseolus vulgaris is described which has been found to be widespread on the southern slopes of the Meru and Kilimanjaro massifs in northern Tanzania. The symptom occurred on plants growing on freely‐draining soils of moderate pH and has led to complete loss of yield of badly affected plants. Leaves with the bronziug symptom contained large concentrations of iron (>3080 mg/kg) and manganese (>760 mg/kg) considered to be toxic in Phaseolus.     

Iron toxicity in rice—conditions and management concepts

Iron toxicity is a syndrome of disorder associated with large concentrations of reduced iron (Fe²⁺) in the soil solution. It only occurs in flooded soils and hence affects primarily the production of lowland rice. The appearance of iron toxicity symptoms in rice involves an excessive uptake of Fe²⁺ by the rice roots and its acropetal translocation into the leaves where an elevated production of toxic oxygen radicals can damage cell structural components and impair physiological processes. The typical visual symptom associated with these processes is the “bronzing” of the rice leaves and substantial associated yield losses. The circumstances of iron toxicity are quite well established. Thus, the geochemistry, soil microbial processes, and the physiological effects of Fe²⁺ within the plant or cell are documented in a number of reviews and book chapters. However, despite our current knowledge of the processes and mechanisms involved, iron toxicity remains an important constraint to rice production, and together with Zn deficiency, it is the most commonly observed micronutrient disorder in wetland rice. Reported yield losses in farmers' fields usually range between 15% and 30%, but can also reach the level of complete crop failure. A range of agronomic management interventions have been advocated to reduce the Fe²⁺ concentration in the soil or to foster the rice plants' ability to cope with excess iron in either soil or the plant. In addition, the available rice germplasm contains numerous accessions and cultivars which are reportedly tolerant to excess Fe²⁺. However, none of those options is universally applicable or efficient under the diverse environmental conditions where Fe toxicity is expressed. Based on the available literature, this paper categorizes iron‐toxic environments, the steps involved in toxicity expression in rice, and the current knowledge of crop adaptation mechanisms in view of establishing a conceptual framework for future constraint analysis, research approaches, and the targeting of technical options.     

The relationship of soil and leaf nutrients to rice leaf oranging

A symptom called leaf‐oranging, indicating a deficiency of many nutrients, occurs in paddy rice (Oryzasativa L.) when production expands into some upland soils. Rice (Gui Chou cv.) was grown in culture pots in a flooded, weathered, upland soil (Nacogdoches) and compared to rice growth in a flooded soil currently used for paddy rice production (Dacosta) in Texas to understand the soil and plant factors involved in leaf‐oranging. Fertilizer rates of 0, 10, and 100 mg N/kg as (NH₄)₂SO₄ were applied to each soil along with phosphorus (P) and potassium (K) fertilizer. The orange Leaf Index (OLI), a measure of leaf‐oranging, was determined weekly and increased to 60–70% for plants grown in the upland soil but its progression was delayed by higher N treatments. No leaf‐oranging was observed in the paddy soil. The soil evoking leaf‐oranging was low in silicon (Si) and high in iron (Fe). In addition, analysis of leaves from these plants showed 19–25% higher leaf ammonium‐nitrogen (NH₄‐N), 9–137% higher manganese (Mn) levels and lower total N:NH₄ concentration compared to normal rice leaves four weeks after transplanting. This inferred that leaf‐oranging probably was associated with some degree of NH₄‐N toxicity and antagonism with K. Leaf‐oranging was also associated with low calcium (Ca) assimilation or Ca uptake inhibition because of the heavy Fe‐oxide coating of the roots of the affected rice plants. In this experiment, leaf‐oranging was not associated with toxic levels of Fe or Mn.     

Ammonium toxicity in chrysanthemum: Critical level and symptoms

Abstract

Three experiments were conducted to determine the critical meq NH₄/meq K ratio in fresh tissue indicative of ammonium toxicity and the symptoms of the same under winter and summer conditions. Three and four levels each of ammonical N and K fertilization were employed in factorial designs. The chrysanthemum cultivars Bright Golden Anne and Yellow Mandalay were studied.

Results indicate there was a critical range of NH₄/K ratios from .025 to .026 below which NH₄ injury never occurred and above which injury always occurred. The occurrence of injury within the range was erratic. Confidence limits for the critical range, based on one standard deviation as determined in Experiment 3, extend from .022 to .029. This range was applicable from the second to ninth week of plant growth and for winter crops as well as the summer crop. Symptoms of toxicity include reduction in growth rate, the development of small necrotic spots beginning on middle to lower leaves and progressing up the plant, thickened‐leathery leaves, reduction in root growth, brown roots, and eventual death of the plant.     

水淹条件下水稻土中砷的生物化学行为研究进展

水稻土中砷的氧化还原和甲基化等生物化学过程是影响水稻砷毒性的主要作用机制;同时,水淹厌氧条件是驱动水稻土中砷的生物化学过程关键环节,且是导致水稻对砷大量吸收累积的主要原因,对以水稻为主食的人们造成健康威胁。本文综述了水稻土中砷的氧化还原和甲基化现象、砷的生物化学作用机制以及影响水稻土砷迁移转化的关键因素,并探讨了水淹厌氧条件对水稻土砷代谢微生物群落、微生物基因表达水平以及对砷归趋的影响。最后,展望了未来的研究方向,以期识别不同水管理模式下土壤微环境对水稻土中砷代谢微生物群落结构与基因表达水平的影响机制,为深入理解砷的生物化学行为和降低水稻对砷的吸收累积提供科学的理论参考。     

Rapid gravimetric determination of Si in rice straw

Abstract

The Si content of rice straw is used as a measure of the Si status of rice plants, the growth and grain production of which are reduced when plant Si is low. Straw Si often is determined gravimetrically following digestion of plant tissue. A new, rapid gravimetric procedure has been developed for determining Si in rice straw. The straw is oxidized, washed free of various components, and SiO₂is developed and weighed in fritted glass Gooche crucibles. The rapid method reduces the analysis time, reduces glassware requirements, and eliminates analyte transfers.     

A quick and efficient screen for resistance to iron toxicity in lowland rice

Iron (Fe) toxicity is a major stress to rice in many lowland environments worldwide. Due to excessive uptake of Fe²⁺ by the roots and its acropetal translocation into the leaves, toxic oxygen radicals may form and damage cell structural components, thus impairing physiological processes. The typical visual symptom is the “bronzing” of the rice leaves, leading to substantial yield losses, particularly when toxicity occurs during early vegetative growth stages. The problem is best addressed through genotype improvement, i.e., tolerant cultivars. However, the time of occurrence and the severity of symptoms and yield responses vary widely among soil types, years, seasons, and genotypes. Cultivars resistant in one system may fail when transferred to another. Better targeting of varietal improvement requires selection tools improving our understanding of the resistance mechanisms and strategies of rice in the presence of excess iron. A phytotron study was conducted to develop a screen for seedling resistance to Fe toxicity based on individual plants subjected to varying levels of Fe (0–3000 mg L^–1 Fe supplied as Fe(II)SO₄), stress duration (1–5 d of exposure), vapor‐pressure deficit (VPD; 1.1 and 1.8 kPa), and seedling age (14 and 28 d). Genotypes were evaluated based on leaf‐bronzing score and tissue Fe concentrations. A clear segregation of the genotypic tolerance spectrum was obtained when scoring 28 d old seedlings after 3 d of exposure to 2000 mg L^–1 Fe in a high‐VPD environment. In most cases, leaf‐bronzing scores were highly correlated with tissue Fe concentration (visual differentiation in includer and excluder types). The combination of these two parameters also identified genotypes tolerating high levels of Fe in the tissue while showing only few leaf symptoms (tolerant includers). The screen allows selecting genotypes with low leaf‐bronzing score as resistant to Fe toxicity, and additional analyses of the tissue Fe concentration of those can identify the general adaptation strategy to be utilized in breeding programs.     

Determination of Fe2+ in Rice Leaves (Oryza sativa L.) by Using the Chelator BPDS Alone or Combined with the Chelator EDTA

Abstract

Iron toxicity is a problem in many areas of wetland rice. Since Fe²⁺ is considered to be the toxic form of iron, the objective of this research was to determine the Fe²⁺ concentration in rice leaves using the chelator bathophenanthroline disulfonate (BPDS), disodium salt alone or combined with the chelator ethylenediaminetetraacetate (EDTA), disodium salt, where BPDS should solely chelate the Fe²⁺ and EDTA chelate only Fe³⁺. Thus, the combination of these chelators should stabilize the Fe oxidation states. It was also tested whether the chelators BPDS and EDTA could stabilize the oxidation states of Fe during the extraction of rice leaves. Extractions of rice leaves were carried out using an 1 mM BPDS or BPDS‐EDTA extractant solution. To test the stabilization of the Fe oxidation states by the combination of BPDS with EDTA, the extraction solution for one part of the samples contained 0.07 mM Fe³⁺. An extraction without plant material as control was also taken into consideration. The results indicated that the chelators were able to stabilize the oxidation states of Fe in the control (extraction without plant material). However, in the presence of plant material, Fe³⁺ was partly reduced to Fe²⁺, i.e., the chelators could not stabilize the oxidation states of Fe. Accordingly, we concluded that the BPDS‐EDTA method may function for the Fe²⁺ determination in water and soil, but it is apparently not suited for rice leaves.     

Critical limits of deficiency and toxicity of zinc in paddy in a typic Ustipsamment

Abstract

A pot culture experiment was conducted to establish the critical limits of deficiency and toxicity of Zn in a Typic Ustipsamment from tropical India. Critical limits of Zn deficiency and toxicity were 0.39, and 12 μg/g with DTPA‐TEA‐CaCl₂, 2.2 and 26 μg/g with EDTA‐(NH₄)₂Co₃ and 0.78 and 12 μg/g with HC1 (0.05 N), respectively. Critical concentrations in the rice plants associated with deficiency and toxicity were 16 and 190 μg/g.     

Effect of Straw Incorporation on 15N‐Labeled Ammonium Nitrogen Uptake and Rice Growth

Abstract

A greenhouse experiment was conducted to determine the effect of rice straw residue on growth and uptake of added ¹⁵N‐labeled ammonium nitrogen (NH₄‐N) (3% ¹⁵N abundance at the rate of 150 kg N ha^?) by rice in Crowley silt loam soil (Typic Albaqualfs). Higher rates of rice straw addition had an adverse affect on plant growth from the first to sixth week. After 6 weeks, the high rice straw treatment had a positive effect on plant growth (P<0.05). The ¹⁵N‐labeled ammonium or fertilizer nitrogen (N) uptake by rice was significantly lower (P<0.05) in the high rice straw treatment as compared to lower rice straw treatments. Greater plant growth was recorded under alternate flooding and draining condition as compared to continuously flooded treatment (P<0.01).     

Potentially hazardous element accumulation in rice tissues and their availability in soil systems after biochar amendments

Purpose

Biochar has shown to be a great product to control the bioavailability of potentially hazardous elements (PHE) in contaminated soils. Despite the advantages associated with the application of biochar in agricultural soils, relatively few studies have focused on the effects of biochar amendments on soil chemical properties, accumulation of arsenic, cadmium, zinc, and lead in rice tissues, and their availability in soil systems.

Materials and methods

The field experiment was conducted at the paddy soils in Hunan Province, China. The soil texture was sandy clay loam. Wheat-derived biochar was applied once to the experimental plots at the rates of 0, 10, 20, 30 and 40 t ha^?1, and referenced as A0, A10, A20, A30, and A40, respectively. For PHE determination, soil samples and plant samples were digested with a mixed solution of HCl:HNO₃ (4:1, V:V) and HCl:HClO₄ (4:1, V:V), respectively, and the arsenic, cadmium, zinc, and lead in the digest solution were measured by ICP-MS (Thermo Fisher Scientific, USA). The soil available fraction of PHE (arsenic, cadmium, zinc, and lead) was extracted by diethylenetriamine pentaacetic acid (DTPA) and measured by inductively ICP-MS.

Results and discussion

Biochar amendment increased chemical properties of soil organic matter, pH, electrical conductivity, cation exchange capacity, nitrate nitrogen, and available phosphorus. Soil DTPA extractable arsenic, cadmium, zinc, and lead concentrations were significantly reduced. Arsenic, cadmium, zinc, and lead in rice shoots, and arsenic, cadmium, and zinc in roots significantly decreased after amendment. Concentrations in rice tissues positively and negatively correlated with the soil available fraction of PHE and soil chemical properties, respectively. Soil electrical conductivity negatively correlated with the soil available fraction of PHE. Concentrations of arsenic, zinc, cadmium, and lead in rice roots declined relative to increases of cation exchange capacity (arsenic, zinc), available phosphorus (cadmium), and nitric nitrogen (lead) content. Similar relationships were observed between cation exchange capacity and PHE in shoots.

Conclusions

Biochar creates avoidance of PHE through regulating chemical properties through biochar sorption capacity. Cation exchange capacity, available phosphorus, and nitric nitrogen were the principle factors affecting roots uptake of arsenic, zinc, cadmium, and lead. Biochar soluble salts could decline availability of metals/metalloids in soils through precipitation. Wheat-derived biochar application is an alternative safe product to immobilize PHE in rice paddy soils by restricting the risk of PHE.