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硒与重金属互作的植物根际过程研究进展
The Interaction of Selenium and Heavy Metals in Rhizosphere Soil: Research Progress
文章归纳了根际环境中硒与重金属的相互作用及其机理,明确了根际土壤中硒和重金属的主要形态及其影响因素。探讨了根际微环境对硒与重金属的影响,并详细叙述了硒与重金属元素的直接互作,以及通过根表铁膜、土壤固相、Eh、pH、根际微生物、根系分泌物等因素发生的间接互作。分析了根际微域中引起硒或重金属形态转化及其含量变化的土壤理化因子,并在此基础上,指出未来硒与土壤重金属互作的研究可向根际微环境深入,建议结合色谱、高通量测序等技术研究根系分泌物、根际微生物群落结构特征等在硒与重金属互作过程中的作用。同时指出,将硒与重金属互作研究成果应用于重金属污染农田土壤治理,既有助于拓展硒在农业生态环境中的应用领域,也为重金属污染农田的绿色修复提供新思路和新方法。
The interaction and mechanism of selenium and heavy metals in the rhizosphere environment were summarized, the main forms and influencing factors of selenium and heavy metals in the rhizosphere were clarified, and the effects of the rhizosphere environment on the selenium and heavy metals were discussed. Direct interaction between selenium and heavy metals and indirect interaction between them through environmental factors such as iron plaque, soil solid phase, Eh, pH, rhizosphere microorganism, and root exudates were described in detail, and the physical and chemical factors of soil causing the change of morphological transformation and content of selenium and heavy metals in the rhizosphere were analyzed. On this basis, it is pointed out that the research on the interaction between selenium and heavy metals in soil should focus on the rhizosphere environment, and the role of root exudates and rhizosphere microbial community structure characteristics in the interaction between selenium and heavy metals should be studied by combining techniques such as chromatography and high-throughput sequencing. At the same time, it is suggested that applying the research results of the interaction between selenium and heavy metals to the heavy metals contaminated farmland will not only expand the application of selenium in the agricultural ecological environment but also provide new methods for the green restoration of heavy metal contaminated farmland.
硒 / 重金属 / 根际 / 土壤 / 农作物 {{custom_keyword}} /
selenium / heavy metals / rhizosphere / soil / crop {{custom_keyword}} /
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城市土壤深受人为活动的影响,具有明显的重金属人为富积的特点,认识这些土壤重金属丰度、形态与土壤理化性质及周围环境因子的关系,有助于更好地保护和修复城市土壤生态系统.本文对南京城市土壤中Pb、Zn、Cu、Cd四种重金属元素的含量和形态特征进行了研究,并用灰色系统理论方法对南京城市土壤重金属污染的影响因子进行了灰色关联度分析,认为最主要影响因子是距工业区远近,其次是土壤粘粒含量、pH值,而交通车流量、生产生活废弃物在土壤中堆埋的比例和土壤有机质对城市土壤重金属污染的影响相对较小.
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Selenium (Se) is an essential micronutrient for many organisms, including plants, animals and humans. As plants are the main source of dietary Se, plant Se metabolism is therefore important for Se nutrition of humans and other animals. However, the concentration of Se in plant foods varies between areas, and too much Se can lead to toxicity. As we discuss here, plant Se uptake and metabolism can be exploited for the purposes of developing high-Se crop cultivars and for plant-mediated removal of excess Se from soil or water. Here, we review key developments in the current understanding of Se in higher plants. We also discuss recent advances in the genetic engineering of Se metabolism, particularly for biofortification and phytoremediation of Se-contaminated environments.
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We investigated the effects of arsenic species on As accumulation, plant growth and rhizospheric changes in As-hyperaccumulator Pteris vittata (PV). PV was grown for 60-d in a soil spiked with 200 mg kg(-1) arsenate (AsV-soil) or arsenite (AsIII-soil). Diffusive gradients in thin films technique (DGT) were used to monitor As uptake by PV. Interestingly AsIII-soil produced the highest PV biomass at 8.6 g plant(-1), 27% and 46% greater than AsV-soil and the control. Biomass increase was associated with As induced P uptake by PV. Although AsIII was oxidized to AsV during the experiment, As species impacted As accumulation by PV, with 17.5% more As in AsIII-soil than AsV-soil (36 vs. 31 mg plant(-1)). As concentration in PV roots was 30% higher in AsV-soil whereas As concentration in PV fronds was 7.9% greater in AsIII-soil, suggesting more rapid translocation of AsIII than AsV. These findings were important to understand the mechanisms of As uptake, accumulation and translocation by PV. Published by Elsevier Ltd.
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The effect of heavy metals Cu and Zn on dehydrogenase and protease activity of the substrate during vermicomposting was investigated. Three dosages of Cu and Zn were tested in mesocosm experiments to investigate their bioaccumulation and impact on the reproduction of Eisenia fetida. Cu accumulated within the worm tissues in dosage concentrations up to a maximum level of 213 mg Cu kg(-1). The number of juveniles decreased from the lowest to highest dosages of Cu and Zn after 10 weeks of the experiment. Dehydrogenase showed a strong negative correlation (P < 0.01) with increased dosage of Cu, while protease remained unaffected. An overall reduction on dehydrogenase activity with increasing dosages of Cu and Zn indicated that these metals would impact detrimentally on the soil microbiology and consequently the stabilisation of the dosed media.
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史雅静, 史雅娟, 王玉荣, 等. 土壤酶对外源有机硒和无机硒的动态响应[J]. 环境科学学报, 2018,38(3):1189-1196.
通过室内非作物连续培养，研究了不同剂量、不同形态外源硒（亚硒酸钠、硒代蛋氨酸）对土壤脲酶、蔗糖酶、中性磷酸酶活性影响的动态变化过程.结果表明，低剂量（10 mg·kg-1）无机硒（亚硒酸钠）对土壤脲酶和蔗糖酶活性有先激活后抑制作用，对土壤中性磷酸酶活性有激活作用.而相同剂量有机硒（硒代蛋氨酸）处理时，3种酶均表现为不同程度的激活状态.高剂量（>30 mg·kg-1）无机硒（亚硒酸钠）处理时，3种酶活性均表现先激活后抑制，其中对脲酶影响最大，对蔗糖酶影响次之，对中性磷酸酶影响最小.而施入高剂量（>30 mg·kg-1）有机硒（硒代蛋氨酸）后，对土壤中脲酶、蔗糖酶的激活作用明显大于无机硒的影响，但对磷酸酶的影响不明显.试验充分说明施入不同剂量、不同形态的外源硒，土壤酶活性表现出不同的动态响应，并且有机硒比无机硒更有利于土壤微生物的生长，能提高土壤酶活性，促进N、P、C养分在土壤生态系统的循环.用有机硒替代无机硒作为外源硒源，有望成为未来发展方向.
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Selenium is an essential trace element for humans and other animals, and there is mounting evidence for the efficacy of certain forms of selenium as cancer-chemopreventive compounds. However, over the years, numerous elements such as As, Cu, Zn, Cd, Hg, Sn, Pb, Ni, Co, Sb, Bi, Ag, Au, and Mo have been found to inhibit anti-carcinogenic effects of selenium, which may affect the anti-carcinogenic activity of selenium. The interaction between selenium and arsenic has been one of the most extensively studied. The proposed mechanisms of this interaction include the increase of biliary excretion and direct interaction/precipitation of selenium and arsenic, and their effects on zinc finger protein function, cellular signaling and methylation pathways. This article focuses on these proposed mechanisms and how anti-carcinogenic effects of selenium may be affected by arsenic.
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A great number of studies have confirmed that mercury-selenium (Hg-Se) antagonism is a widespread phenomenon in microorganisms, fish, poultry, humans, and other mammals. However, by comparison, little attention has been paid to plants. To investigate the influence of Se on the uptake and translocation of methylHg/inorganic Hg (MeHg/IHg) in the rice-soil system, we determined the levels of Se, IHg, and MeHg in different parts of rice plants (including the root, stem, leaf, husk, and grain (brown rice)) and corresponding soils of root zones collected from a Hg mined area, where Hg and Se co-occur due to historic Hg mining and retorting activities. The results showed that, in general, the Se levels were inversely related to the levels of both IHg and MeHg in the grains. In addition, a consistent reduction in translocation of both IHg and MeHg in the aerial shoots (i.e., the stem, leaf, husk, and grain) with increasing Se levels in the soils was observed. Furthermore, the Se levels were positively correlated with the IHg levels in the soils and the roots. These results suggest that Se may play an important role in limiting the bioaccessibility, absorption, and translocation/bioaccumulation of both IHg and MeHg in the aerial rice plant, which may be related to the formation of an Hg-Se insoluble complex in the rhizospheres and/or roots.
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刘达, 涂路遥, 赵小虎, 等. 镉污染土壤施硒对植物生长及根际镉化学行为的影响[J]. 环境科学学报, 2016,36(3):999-1005.
采用根箱培养的方式,研究了在不同镉污染水平(0.5 mg·kg-1、5 mg·kg-1土壤)的酸性黄棕壤中施用外源硒对小白菜生长、光合特性及根际土壤中镉的化学行为影响.结果表明:镉污染土壤中施硒可显著增加小白菜的生物量,增强小白菜叶片的光合速率和蒸腾速率;镉污染严重时,施硒还可提高小白菜的气孔导度;施用适量硒(0.25 mg·kg-1)可显著降低小白菜地上部镉含量,其中镉污染浓度较低(0.5 mg·kg-1)时,该效果达显著水平.在镉污染程度低(0.5 mg·kg-1)的土壤施用适量硒(0.25 mg·kg-1),可显著降低土壤交换态镉含量,其中,根际和非根际土壤交换态Cd含量分别降低了22.20%和43.79%.外源Se有效地降低了土壤Cd的生物有效性,这种作用在Se的施用浓度较低时表现更加明显;当Cd污染浓度较高时,土壤Cd形态分布相对稳定,外源Se对根际和非根际土壤Cd形态分布的影响不显著.研究结果为深入揭示Se对菜地Cd污染的调控机理提供理论参考.
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Greenhouse experiment was conducted to examine effects of arsenic (As) on iron plaque formation, radial oxygen loss, As accumulation, and speciation in rice. Three genotypes were grown in soil with three different concentrations of As. The stress of As caused a slight increase of iron plaque formation (P>0.05) and a decrease in the rates of radial oxygen loss (ROL; P<0.01). The results of As speciation showed that the percentages of DMA increased from 19-28 % to 53-58 %, while the percentages of inorganic As decreased from 53-58 % to 36-42 % with the increasing soil As concentrations, indicating a strong environmental influence on As species in rice grain. The present study showed that elevated soil As may induce As toxicity towards rice plants, leading to the decrease of ROL; environmental factors could influence As methylation or As species transportation. Our study provided useful information on As tolerance and accumulation in rice which may contribute to reducing the health risk posed by As contamination in rice.
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MAIN CONCLUSION: Iron plaque on root surfaces greatly influenced selenium uptake and played different roles in selenite and selenate uptake. Iron plaque commonly forms on rice root surfaces under flooded conditions, but little is known about the relationship between iron plaque and selenium (Se) accumulation. Here, we investigate the effects of iron plaque on Se uptake by and translocation within rice (Oryza sativa) seedlings, and the kinetics of selenite and selenate influx into rice roots (with or without iron plaque) were determined in short-term (30 min) experiments. Rice seedlings were planted in nutrient solutions containing different levels of ferrous ion for 3 days and then transplanted into nutrient solutions with selenite or selenate. Se concentrations in iron plaque were positively associated with the amounts of iron plaque in both selenite and selenate treatments and iron plaque had a higher affinity for selenite than selenate. Results showed that iron plaque on root surfaces greatly influenced Se uptake and played different roles in selenite and selenate uptake. The selenite and selenate uptake kinetics results demonstrated that the presence of iron plaque enhanced selenite uptake, but decreased selenate uptake. In addition, root-Se concentrations increased with the increasing amounts of iron plaque, but Se translocation from roots to shoots was reduced with the increasing amounts of iron plaque in the +selenite treatment. Iron plaque significantly influenced selenite uptake and might act as a pool to selenite accumulation in rice plants. However, iron plaque had no significant effect on selenate uptake or even as a barrier to selenate uptake.
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The aim of this study was to investigate the role of microorganisms on the behaviour of selenium in natural soil maintained under strictly aerobic conditions. Six-day batch experiments were performed with soils constrained to different microbiological states, either by sterilisation or by adding organic substrates. Selenium was added to the soil as selenite. The distribution of selenium in the gaseous, liquid and solid phases of the batch was measured. Selenium partitioning between the various solid phases was investigated by chemical sequential extractions. Active microorganisms played major effects on the distribution of selenium within the soil. On the one hand, microorganisms could promote selenium volatilisation (in relatively small amounts), leading to the spreading of selenium compounds outside the soil. On the other hand, microbial activities increased both amount of selenium retained by the soil and the strength of its retention (less exchangeable selenium), making selenium less susceptible to remobilisation.
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The behavior of As in paddy fields is of great interest considering high As contents of groundwater in several Asian countries where rice is the main staple. We determined the concentrations of Fe, Mn, and As in soil, soil water, and groundwater samples collected at different depths down to 2 m in an experimental paddy field in Japan during the cycle of flooded and non-flooded periods. In addition, we measured the oxidation states of Fe, Mn, and As in situ in soil samples using X-ray absorption near-edge structure (XANES) and conducted sequential extraction of the soil samples. The results show that Fe (hydr)oxide hosts As in soil. Arsenic in irrigation waters is incorporated in Fe (hydr)oxide in soil during the non-flooded period, and the As is quickly released from soil to water during the flooded period because of reductive dissolution of the Fe (hydr)oxide phase and reduction of As from As(V) to As(III). The enhancement of As dissolution by the reduction of As is supported by high As/Fe ratios of soil water during the flooded period and our laboratory experiments where As(III) concentrations and As(III)/As(V) ratios in submerged soil were monitored. Our work, primarily based on data from an actual paddy field, suggests that rice plants are enriched in As because the rice grows in flooded paddy fields when mobile As(III) is released to soil water.
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Selenium (Se) alleviates cadmium (Cd) accumulation in several plants. Nevertheless, it is still unclear why it has such effect. Thus, this study aimed to investigate the effects of Se on soil Cd bioavailability, and Cd accumulation in flooded rice plants, and to determine the mechanisms underlying these effects. Concentration of Cd and Se in different rice tissues was determined along Cd and Se concentrations in the soil solution and soil Cd fractions. Results showed that exogenous selenite and selenate treatments significantly increased rice grain Se by 4.25- and 2.39-fold and decreased Cd by 36.5% and 25.3% relative to control treatment, respectively. The addition of Se to Cd-contaminated soil significantly decreased total Cd concentration in the soil solution by 11.2-13.0%, increased soil pH by 0.06-0.32 units, and enhanced soil Cd immobilization in relation to control. Exogenous Se also reduced diethylenetriaminepentaacetic acid-Cd, exchangeable, and residual Cd but increased the levels of Cd bound to carbonate and iron and manganese oxides. Thus, amending Cd-contaminated soil with Se may help decrease Cd content as well as increase Se levels in rice grain, as Se may mitigate Cd accumulation in rice plants by increasing soil pH, reducing Cd bioavailability, and inhibiting Cd translocation from roots to shoots.
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Rice (Oryza sativa) is the staple food for half of the world's population, but the selenium (Se) concentrations in rice grain are low in many rice-growing regions. This study investigated the effects of water management on the Se speciation dynamics in the soil solution and Se uptake and speciation in rice in a pot experiment. A control containing no Se or 0.5 mg kg(-1) of soil of selenite or selenate was added to the soil, and plants were grown under aerobic or flooded conditions. Flooding soil increased soluble Se concentration when no Se or selenite was added to the soil, but decreased it markedly when selenate was added. Selenate was the main species in the +selenate treatment, whereas selenite and selenomethionine selenium oxide were detected in the flooded soil solutions of the control and +selenite treatments. Grain Se concentration was 49% higher in the flooded than in the aerobic treatments without Se addition. In contrast, when selenate or selenite was added, the aerobically grown rice contained 25- and 2-fold, respectively, more Se in grain than the anaerobically grown rice. Analysis of Se in rice grain using enzymatic hydrolysis followed by HPLC-ICP-MS and in situ X-ray absorption near-edge structure (XANES) showed selenomethionine to be the predominant Se species. The study showed that selenate addition to aerobic soil was the most effective way to increase Se concentration in rice grain.
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滕应, 骆永明, 李振高. 污染土壤的微生物修复原理与技术进展[J]. 土壤, 2007(4):497-502.
微生物修复是土壤环境生物修复技术的重要组成部分,是最具发展和应用前景的生物学环保新技术.本文以土壤中重金属及典型有机污染物为对象,从土壤微生物与污染物质的相互作用入手,较为系统地综合评述国内外污染土壤的微生物修复原理与技术,并结合当前土壤污染的新特点,提出了需进一步认识和解决微生物修复过程中出现的新现象和新问题,以不断丰富和拓展土壤环境微生物修复范畴与内涵.
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Iron reduction and mercury methylation by dissimilatory iron-reducing bacteria (DIRB), Geobacter sulfurreducens and Shewanella oneidensis, were studied, and the relationship of mercury methylation coupled to iron reduction was determined. The ability of both bacteria for reducing iron was tested, and Fe(III) reduction occurred with the highest rate when ferric oxyhydroxide was used as a terminal electron acceptor. G. sulfurreducens had proven to mediate the production of methylmercury (MeHg), and a notable increase of MeHg following the addition of inorganic Hg was observed. When the initial concentration of HgCl2 was 500nM, about 177.03nM of MeHg was determined at 8d after G. sulfurreducens inoculation. S. oneidensis was tested negligible for Hg methylation and only 12.06nM of MeHg was determined. Iron reduction could potentially influence Hg methylation rates. The increase in MeHg was consistent with high rate of iron reduction, indicating that Fe(III) reduction stimulated the formation of MeHg. Furthermore, the net MeHg concentration increased at low Fe(III) additions from 1.78 to 3.57mM, and then decreased when the added Fe(III) was high from 7.14 to 17.85mM. The mercury methylation rate was suppressed with high Fe(III) additions, which might have been attributable to mercury complexation and low availability.
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Charlotte,
Inorganic arsenic (iAs) is a ubiquitous human carcinogen, and rice (Oryza sativa) is the main contributor to iAs in the diet. Methylated pentavalent As species are less toxic and are routinely found in plants; however, it is currently unknown whether plants are able to methylate As. Rice, tomato (Solanum lycopersicum) and red clover (Trifolium pratense) were exposed to iAs, monomethylarsonic acid (MMA(V)), or dimethylarsinic acid (DMA(V)), under axenic conditions. Rice seedlings were also grown in two soils under nonsterile flooded conditions, and rice plants exposed to arsenite or DMA(V) were grown to maturity in nonsterile hydroponic culture. Arsenic speciation in samples was determined by HPLC-ICP-MS. Methylated arsenicals were not found in the three plant species exposed to iAs under axenic conditions. Axenically grown rice was able to take up MMA(V) or DMA(V), and reduce MMA(V) to MMA(III) but not convert it to DMA(V). Methylated As was detected in the shoots of soil-grown rice, and in rice grain from nonsterile hydroponic culture. GeoChip analysis of microbial genes in a Bangladeshi paddy soil showed the presence of the microbial As methyltransferase gene arsM. Our results suggest that plants are unable to methylate iAs, and instead take up methylated As produced by microorganisms.
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Methylated arsenic (As) species are a common constituent of rice grains accounting for 10-90% of the total As. Recent studies have shown that higher plants are unlikely to methylate As in vivo suggesting that As methylation is a microbial mediated process that occurs in soils prior to plant uptake. In this study, we designed primers according to the conserved essential amino acids and structural motifs of arsenite S-adenosylmethionine methyltransferase (ArsM). We report for the first time the successful amplification of the prokaryotic arsM gene in 14 tested soils with wide ranging As concentrations. The abundance and diversity of the arsM gene in the rice rhizosphere soil and roots were analyzed using the designed primers. Results showed that microbes containing arsM genes were phylogenetically diverse, as revealed by the clone library and terminal restriction fragment length polymorphism (T-RFLP) analysis, and were branched into various phyla. Concentration of methylated As species in the soil solution was elevated in the rhizosphere soil and also by the addition of rice straw into the paddy soil, corresponding to the elevated abundance of the arsM gene in the soil. These results, together with evidence of horizontal gene transfer (HGT) of the arsM gene, suggest the genes encoding ArsM in soils are widespread. These findings demonstrate why most rice, when compared with other cereals, contains unusually high concentrations of methylated As species.
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黄艺, 陈有键, 陶澍. 菌根植物根际环境对污染土壤中Cu、Zn、Pb、Cd形态的影响[J]. 应用生态学报, 2000(3):431-434.
采用根垫法和连续形态分析技术,分析了生长在污灌土壤中菌根小麦和无菌根小麦根际Cu、Zn、Pb、Cd的形态分布和变化趋势.结果表明,与对照土壤相比,菌根际土壤中交换态Cu含量显著增加,交换态Cd呈减少的趋势;与非菌根际相比,Cu、Zn、Pb的有机结合态在菌根根际中显著增加,而4种测定金属的碳酸盐态和铁锰氧化态都没有显著改变.该结果表明,植物根系能影响根际中金属形态的变化,且菌根比无菌根的影响程度大.在土壤金属浓度过量的情况下,菌根可通过调节根际中金属形态从而调节土壤中金属的生物有效性.文章还讨论了菌根引起重金属形态改变的原因
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The trace metal selenium is in demand for health supplements to human and animal nutrition. We studied the reduction of selenite (SeO(3)(-)(2)) to red elemental selenium by Rhodopseudomonas palustris strain N. This strain was cultured in a medium containing SeO(3)(-)(2) and the particles obtained from cultures were analyzed using transmission electron microscopy (TEM), energy dispersive microanalysis (EDX) and X ray diffraction analysis (XRD). Our results showed the strain N could reduce SeO(3)(-)(2) to red elemental selenium. The diameters of particles were 80-200 nm. The bacteria exhibited significant tolerance to SeO(3)(-)(2) up to 8.0 m mol/L concentration with an EC(5)(0) value of 2.4 m mol/L. After 9 d of cultivation, the presence of SeO(3)(2)(-) up to 1.0 m mol/L resulted in 99.9% reduction of selenite, whereas 82.0% (p<0.05), 31.7% (p<0.05) and 2.4% (p<0.05) reduction of SeO(3)(-)(2) was observed at 2.0, 4.0 and 8.0 m mol/L SeO(3)(2)(-) concentrations, respectively. This study indicated that red elemental selenium was synthesized by green technology using Rhodopseudomonas palustris strain N. This strain also indicated a high tolerance to SeO(3)(-)(2). The finding of this work will contribute to the application of selenium to human health.
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许玉凤, 曹敏建, 王文元, 等. 植物耐铝毒害的研究进展[J]. 沈阳农业大学学报, 2002(6):452-455.
综述了土壤中铝的存在形态、铝对植物产生的毒害以及植物的抗铝毒机理。由于植物的耐铝毒特性受遗传控制，因此通过基因型筛选获得耐铝毒的基因型材料，对于提高酸性土壤上的作物生产力具有重要意义。
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杨仁斌, 曾清如, 周细红, 等. 植物根系分泌物对铅锌尾矿污染土壤中重金属的活化效应[J]. 农业环境保护, 2000(3):152-155.
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Indian mustard (Brassica juncea L.) accumulates high tissue Se concentrations and volatilizes Se in relatively nontoxic forms, such as dimethylselenide. This study showed that the presence of bacteria in the rhizosphere of Indian mustard was necessary to achieve the best rates of plant Se accumulation and volatilization of selenate. Experiments with the antibiotic ampicillin showed that bacteria facilitated 35% of plant Se volatilization and 70% of plant tissue accumulation. These results were confirmed by inoculating axenic plants with rhizosphere bacteria. Compared with axenic controls, plants inoculated with rhizosphere bacteria had 5-fold higher Se concentrations in roots (the site of volatilization) and 4-fold higher rates of Se volatilization. Plants with bacteria contained a heat-labile compound in their root exudate; when this compound was added to the rhizosphere of axenic plants, Se accumulation in plant tissues increased. Plants with bacteria had an increased root surface area compared with axenic plants; the increased area was unlikely to have caused their increased tissue Se accumulation because they did not accumulate more Se when supplied with selenite or selenomethionine. Rhizosphere bacteria also possibly increased plant Se volatilization because they enabled plants to overcome a rate-limiting step in the Se volatilization pathway, i.e. Se accumulation in plant tissues.
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