The combined treatment of Mn and Al alleviates the toxicity of Al or Mn stress alone in barley

Aluminum (Al) and manganese (Mn) toxicity commonly coexists in acid soil, so the crop cultivars suitable for planting in acid soil should show high tolerance to both elements simultaneously. However, it is still not clear if the toxicity of Mn and Al on plant growth is antagonistic or synergistic, and the plants with Al tolerance are also tolerant to Mn toxicity. In this study, three barley genotypes (one Tibetan wild and two cultivated), differing in Al tolerance, were characterized for growth and physiological responses to Al or Mn toxicity as well as the combined treatment of the two toxic elements. Interestingly, it has been found that the combined treatment of both metals was less affected in comparison with Al or Mn treatment alone, in terms of plant growth, Al or Mn concentration in plant tissues, and photosynthetic parameters, indicating antagonistic interaction of Al and Mn for their effect on plant growth and physiological traits. The results also showed that there was a dramatic difference among barley genotypes in Mn toxicity tolerance and XZ16 showed much higher tolerance than other two genotypes. High Mn tolerance is mainly described to less Mn uptake and lower Mn concentration in plants, and Mn tolerance is independent of Al tolerance.     

Response ofAnabaena doliolum to bimetallic combinations of Cu,Ni and Fe with special reference to sequential addition

This study reports physiological features of a N₂-fixing cyanobacteriumAnabaena doliolum in response to metal mixtures. Exposure of the cyanobacterium to Cu, Ni and Fe individually, as well as in combinations (Cu + Ni, Cu + Fe, Ni + Fe), showed marked differences in growth inhibition, nutrient uptake (NH₄ ⁺ and NO₃ ⁻), photosynthesis, ATP content, nitrate reductase, glutamine synthetase and urease activities. The response to metal combinations was also dependent upon the order in which the metals were added. The Cu-Ni combination resulted in synergistic interaction, in contrast to the antagonism of Cu-Fe and Ni-Fe. Pre-addition of Fe protected the cyanobacterium against Cu and Ni toxicity. Statistically significant (P < 0.005) inhibition of all the processes following metal supplementation was observed. This study suggests that carbon fixation is the most suitable variable for assessing heavy metal toxicity.     

亚热带湿地松叶片多元素化学计量与养分回收对氮添加的短期响应

在我国南方亚热带湿地松人工林设置了3个水平的野外氮添加控制试验(0、40、120 kg N·hm^-2·a^-1),于2014和2015年生长季高峰期(7月底)和末期(10月底)采集湿地松成熟绿叶和落叶,分析外源氮添加对湿地松叶片碳(C)、氮(N)、磷(P)、钾(K)、钙(Ca)、镁(Mg)、铝(Al)、铁(Fe)、锰(Mn)9种元素浓度及其养分回收的影响.结果表明: N添加显著增加了湿地松绿叶中N、Al、Mn浓度,降低了P和2014年的Ca浓度,而对C、K、Mg、Fe 浓度无显著影响.N添加显著提高了绿叶N/P,且该比值及绿叶养分浓度(N、P、Mn)对N添加的响应依赖于N的剂量(高N条件下响应更强).N添加显著降低了2015年N的回收效率,提高了2014年K的回收效率.相比于养分回收效率,回收能力对增加的可利用氮响应更强.N添加显著降低了N的回收能力,提高了P、K的回收能力,降低了枯叶中的Fe浓度,而对枯叶中Ca、Mg、Al、Mn浓度无显著影响.这表明,N添加对叶片化学计量的影响因不同元素而异,植物会通过调整自身的养分内循环(养分回收)来应对环境变化.N添加提高了绿叶N/P和K/P,说明氮添加条件下植物生长可能由N、P共同限制转变为P限制.氮添加增加了绿叶中Al、Mn浓度,表明N添加下湿地松面临潜在的金属离子毒性风险升高.     

Salicylic acid induces amelioration of chromium toxicity and affects antioxidant enzyme activity in Sorghum bicolor L.

Aim: Chromium (Cr(VI)) would inflict serious morphological, metabolic, and physiological anomalies in plants ranging from chlorosis of shoot to lipid peroxidation and protein degradation. Cr(VI) toxicity is often associated with oxidative stress, caused by the excessive formation of reactive oxygen species (ROS). In response, plants are equipped with a repertoire of mechanisms to counteract heavy metal (HM) toxicity. Salicylic acid (SA) plays a key role in the signal transduction pathways of various stress responses, demonstrating the protective effect of SA against abiotic stress factors. So, the present investigation was carried out to study the amelioration of pernicious effects of different concentration of Cr(VI) (0.0, 2.0, and 4.0?mg Cr(VI) kg^?1 soil in the form of potassium dichromate) by treatments of salicylic acid solution viz. pretreatment and foliar spray via antioxidative enzymes and their metabolites.

Results: With different treatments of salicylic acid solution, the reinstatement from ill effects of Cr(VI) toxicity was contemplated but the most conspicuous effect was observed when salicylic acid solution was supplied through the foliar spray (0.50?mM). This was accompanied with an increase in ascorbate peroxidase activity and hydrogen peroxide content and decrease in peroxidase activity and ascorbic acid content.

Significance of the study: This study suggests that salicylic acid when applied through pre-treatment of seeds or through a foliar spray can be used to ameliorate the toxic effects of chromium (VI). Salicylic acid has the great potential for reducing the toxicity of heavy metals without negatively impacting the growth of the plants.     

Metal toxicity and ectomycorrhizas

Metal toxicity (Al and heavy metals) is a major constraint affecting root growth in a number of natural or managed ecosystems. Fine roots of the majority of plant species are associated with mycorrhizal fungi, which may modify the sensitivity of roots to metal stress. In this review, we summarise the available evidence demonstrating beneficial effects of ectomycorrhizas in alleviation of metal toxicity in forest tree seedlings. We identify experimental shortcomings of past research (e.g. the use of shoot metal concentrations as a measure of metal uptake, use of microanalytical techniques biased by element redistribution) that may confound major conclusions drawn from these experiments. Although there is no doubt that in many cases ectomycorrhizal fungi indeed ameliorate metal stress in their host plants, the mechanism(s) involved remain(s) unclear. The role of metal sorption on fungal tissues thought to reduce metal exposure of the host plant is critically reviewed. As direct evidence (both under artificial and soil conditions) supporting a unique role of fungal immobilisation of metals is lacking so far, there is an urgent need to also test alternative tolerance mechanisms such as the release of metal chelating substances, or nutritional and hormonal effects mediated by mycorrhizal fungi.     

Root and shoot elongation as an assessment of heavy metal toxicity and ‘Zn Equivalent Value’ of edible crops

Seeds of thirteen edible plant species were tested for their response to heavy metals during their early development. It was found that a short-term root elongation test of six days could be used to evaluate the degree of toxicity of aqueous samples containing heavy metals. Shoot elongation was found to be less sensitive to metals than root elongation.The seeds were sown in pots containing freshwater sand to which known concentrations of metal solutions were added. The relative toxicity of the three metals, copper, nickel and zinc, followed the pattern of Ni > Cu > Zn.Results on the relative toxicity of Zn : Cu: Ni to various plant species indicated that the ratios were species-specific. The Zn equivalent concept of Zn : Cu : Ni = 1 : 2 : 8 could not be applied to all the plant species tested.The root growth of seeds of Brassica parachinensis (flowering Chinese cabbage) placed on filter papers in petri dishes to which metal solutions were added were tested. The sensitivity ranking of the metals tested was found to be as follows: Ni > Cd > Cu > Al > Fe > Zn > Pb > Mn > Ag. There was no significant difference (p > 0.05) in percentage reduction in root elongation among the four different repeated trials.     

Interactive and cumulative effects of multiple human stressors in marine systems

Humans impact natural systems in a multitude of ways, yet the cumulative effect of multiple stressors on ecological communities remains largely unknown. Here we synthesized 171 studies that manipulated two or more stressors in marine and coastal systems and found that cumulative effects in individual studies were additive (26%), synergistic (36%), and antagonistic (38%). The overall interaction effect across all studies was synergistic, but interaction type varied by response level (community: antagonistic, population: synergistic), trophic level (autotrophs: antagonistic, heterotrophs: synergistic), and specific stressor pair (seven pairs additive, three pairs each synergistic and antagonistic). Addition of a third stressor changed interaction effects significantly in two‐thirds of all cases and doubled the number of synergistic interactions. Given that most studies were performed in laboratories where stressor effects can be carefully isolated, these three‐stressor results suggest that synergies may be quite common in nature where more than two stressors almost always coexist. While significant gaps exist in multiple stressor research, our results suggest an immediate need to account for stressor interactions in ecological studies and conservation planning.     

Behavioural and physiological responses of Gammarus pulex exposed to cadmium and arsenate at three temperatures: individual and combined effects

This study aimed at investigating both the individual and combined effects of cadmium (Cd) and arsenate (AsV) on the physiology and behaviour of the Crustacean Gammarus pulex at three temperatures (5, 10 and 15 °C). G. pulex was exposed during 96 h to (i) two [Cd] alone, (ii) two [AsV] alone, and (iii) four combinations of [Cd] and [AsV] to obtain a complete factorial plane. After exposure, survival, [AsV] or [Cd] in body tissues, behavioural (ventilatory and locomotor activities) and physiological responses (iono-regulation of [Na(+)] and [Cl(-)] in haemolymph) were examined. The interactive effects (antagonistic, additive or synergistic) of binary mixtures were evaluated for each tested temperature using a predictive model for the theoretically expected interactive effect of chemicals. In single metal exposure, both the internal metal concentration in body tissues and the mortality rate increased along metallic gradient concentration. Cd alone significantly impaired both [Na(+)] and [Cl(-)] while AsV alone had a weak impact only on [Cl(-)]. The behavioural responses of G. pulex declined with increasing metal concentration suggesting a reallocation of energy from behavioural responses to maintenance functions. The interaction between AsV and Cd was considered as 'additive' for all the tested binary mixtures and temperatures (except for the lowest combination at 10 °C considered as "antagonistic"). In binary mixtures, the decrease in both ventilatory and locomotor activities and the decline in haemolymphatic [Cl(-)] were amplified when respectively compared to those observed with the same concentrations of AsV or Cd alone. However, the presence of AsV decreased the haemolymphatic [Na(+)] loss when G. pulex was exposed to the lowest Cd concentration. Finally, the observed physiological and behavioural effects (except ventilation) in G. pulex exposed to AsV and/or Cd were exacerbated under the highest temperature. The discussion encompasses both the toxicity mechanisms of these metals and their interaction with rising temperature.     

Effects of Bioavailable Heavy Metal Species,Arsenic, and Acid Drainage from Mine Tailings on a Microbial Community Sampled Along a Pollution Gradient in a Freshwater Ecosystem

Sediment and water samples representing a pollution gradient in a long, narrow lake polluted at one end by heavy metals, arsenic, and acid drainage from mine tailings, together with samples from an unpolluted reference lake, were analyzed to determine effects of pollutants on the microbial community of the polluted lake. Ribosomal ribonucleic acid, fatty acid, and phospholipid analyses, along with assays of CO₂ production, denitrification, and enzyme activities, were performed to characterize the microflora; and environmental conditions were defined by various physicochemical analyses, including determination of bioavailable metal species. Mine waste pollution fostered the growth of Holophagal Acidobacteria, green sulphur bacteria, and α-Proteobacteria but inhibited numerous other types of microorganisms, reducing the overall productivity, biomass, and biodiversity of the microflora. The beneficial effects imply toleration of pollutants, suppression of competing or antagonistic species, and utilization of biogenic sulphide; and the toxic effects are attributable to bioavailable metals, arsenic, and sulphuric acid produced by oxidation of sulphides. The bioavailability and toxicity of sediment-bound metals were evidently increased by acidification, elevation of sediment Eh, and inhibition of metal-immobilizing bacteria by pollutants but were decreased by metal-scavenging oxyhydroxides, sulphide, and organic matter. Metal toxicity also depended on specific metal properties (e.g., electronegativity), providing a basis for inferring mechanisms of toxicity and oxidation states of metals and explaining differences in relative toxicity. The pollutants harmed the ecosystem as a whole by inhibiting microorganisms that performed crucial ecological functions, notably oxygen-releasing photosynthesis, decomposition and humification of organic matter, nutrient recycling, and control of metal availability.     

Fungal Toxicity of Mobilized Soil Aluminum and Manganese

Inhibition of Aspergillus flavus growth from spores was used as a simple bioassay for toxicity of Al and Mn mobilized by simulated acid precipitation. Al was identified as being toxic in soil leachates resulting from acid inputs of pH less than 2.7. Inhibition by Mn was not detectable. The addition of fluoride significantly reduced Al toxicity, suggesting that biotoxicity of Al is partially dependent on the anionic composition of the soil solution.     

刺楸年轮中重金属含量动态变化及富集特性

为探索刺楸对受污染土壤重金属的富集和修复效应, 以南京栖霞山的乡土树种刺楸及其根际周边土壤为研究对象, 截取其根基部年轮盘及根际土壤样本, 采用ICP-AES法测定年轮及土壤样本中重金属(Cu、Cd、Cr、Mn、Ni、Pb、Zn)元素含量。结果表明: 栖霞山样地中的土壤受Mn、Pb和Zn污染最为严重, 存在Cu、Cd、Mn、Pb、Zn元素的高度复合污染, Cd、Cr、Cu、Ni、Zn在土壤和年轮中存在相关性, Mn和Pb则没有表现出明显的相关性; 刺楸修复受Cd、Mn、Pb、Zn污染的土壤效果并不显著, 更适用于Cr、Cu、Ni污染的土壤修复; 鉴于Cu元素含量变化特征, 刺楸也可以作为反映当地污染历史的记录载体; 刺楸年轮中的重金属元素之间存在交互作用, 其中Cd与Zn元素含量高度相关(r=0.984, p<0.01), 在刺楸年轮吸收重金属元素的过程中, Cu与Cd、Cr、Mn、Zn元素具有协同作用, Mn元素对其他元素有一定的拮抗作用。     

Aluminum-mycorrhizal interactions in the physiology of pitch pine seedlings

Aluminum (Al) in the rhizosphere adversely affects plant nutrition and growth. Although many conifer species, and pitch pine (Pinus rigida) in particular, have evolved on acidic soils where soluble Al is often high, controlled environment studies often indicate that Al interferes with seedling growth and nutrient relations. Under normal field conditions, conifer roots grow in a symbiotic relationship with ectomycorrhizal fungi, and this association may modulate the effects of Al on root physiology. To investigate the influence of mycorrhizal infection on Al toxicity, pitch pine seedlings were grown with or without the ectomycorrhizal symbiont Pisolithus tinctorius and were exposed to low levels of Al in sand culture. Aluminum at 50 μM reduced nonmycorrhizal seedling growth and increased foliar Al concentrations, but did not alter photosynthetic gas exchange or other aspects of seedling nutrition. Nonmycorrhizal seedlings exposed to 200 μM Al exhibited decreased growth, increased transpiration rates, decreased water use efficiency, increased foliar Al and Na levels, and reduced foliar P concentrations. Seedlings inoculated with P. tinctorius exhibited unaltered growth, physiological function, and ionic relations when exposed to Al. The fungal symbiont evidently modulated ionic relations in the rhizosphere, reducing Al-P precipitation reactions, Al uptake, and subsequent root and shoot tissue Al exposure.     

HEAVY METALS AND MARINE PHYTOPLANKTON: CORRELATION OF TOXICITY AND SULFHYDRYL-BINDING1,2

In a study of sublethal effects of metals on growth of the marine diatom Asterionella japonica Cleve, the relative toxicities of Hg, Cu, Zn, Pb, Cd, and Mn are shown to be correlated (r = 0.961) with the solubility products of the corresponding metal sulfides. The results, together with findings elsewhere, suggest a common action for these heavy metals, with toxicity deriving from metal binding to sulfhydryl-containing compounds in the cell.     

Synergistic effect of purine derivatives on the toxicity of pyrazofurin and 6-azauridine towards cultured mammalian cells

A novel synergistic effect of several purine derivatives such as adenine, adenosine, hypoxanthine, and guanine on the toxicity of nucleoside analogs pyrazofurin and 6-azauridine towards cultured Chinese hamster ovary (CHO) cells has been observed. The presence of the above purine derivatives enhanced the toxicity of pyrazofurin and 6-azauridine, in a dose dependent manner. The growth inhibitory effects of these nucleoside analogs either alone or in combination with the purine derivatives were reversed by uridine and cytidine, providing evidence that the synergistic effect of the purine derivatives was exerted at the level of pyrimidine nucleotide biosynthesis. Studies with mutant cells lacking various purine phosphorylating enzymes show that phosphorylation of purine derivatives through reactions utilizing phosphoribosylpyrophosate (PRPP) is essential for observing the synergistic response. It is suggested that the above purine derivatives (including adenosine, via conversion to hypoxanthine) exert their synergistic effects by depleting the cellular pool of PRPP by two separate mechanisms (direct utilization and feedback inhibition of its synthesis), which as a result becomes rate limiting in the synthesis of orotidine monophosphate (OMP). The reduced levels of OMP, which is a competing substrate with pyrazofurin- and 6-azauridine-5'-monophosphates for binding to the target enzyme OMP decarboxylase, could then account for the inhibition of the enzyme at lower concentrations of these analogs.     

Effects of acidity on acute toxicity of aluminium-waste and aluminium-contaminated soil

The total heavy metal concentrations of Al-waste and Al-contaminated soil were many times higher than that found in the control soil, which might pose toxic effects on nearby ecosystems under acidic condition. The present study aimed to detect the amount of Al, Cu, Zn, Mn, Pb, Ni and Cd extracted by distilled water and ammonium acetate at pH 3.8, 4.8, 5.8, 6.8 and 7.8. The acute toxicities of water extracts were assessed by two bioassays. Results showed that concentrations of heavy metals, especially Al, were the highest in extracts from Al-contaminated soil extracted with NH₄OAc, followed by Al-waste. The control displayed relatively low levels of metals. More heavy metals were extracted at acidic pH than at neutral pH. Distilled water extracts exhibited lower levels of metals than those extracted with NH₄OAc. The first bioassay, in terms of seed germination and root elongation of B. parachinensis, indicated that the germination rates were seriously retarded by Al-waste even at neutral pH. Less than 25% seeds were germinated in Al-waste and the toxic effect was more obvious at pH 3.8. Root growth in Al-waste and Al-soil was slower than in the control and no seedling in Al-waste had roots longer than 2 cm at the end of this study. In the second bioassay, the photosynthetic rate of Chlorella pyrenoidosa was significantly inhibited by Al-waste when compared with the control, although the pH effect was not clear. This study revealed that the metal availability was pH dependent and their toxicity could be rapidly assessed by two simple bioassays.     

Phosphorus and micronutrient metal uptake by some tree species as affected by phosphate and lime applied to an acid sandy soil

Summary The effects of added P and lime on Douglas fir and Scots pine seedlings, and poplar and willow cuttings growing in a podzolic soil (pH 3.8, 90 ppm total P) were studied in pot experiments. Conifer dry weights responded best to P applied in the absence of lime, whereas liming to pH 4.3 promoted the P response of the broadleaved species. Normal rates of P, and of lime (broad-leaved species), by promoting growth, also raised total contents of P and metals (Zn, Mn, Cu, Fe) in the various plant parts (stems, foliage, roots), but generally lowered the metal concentrations. The results strongly suggest that P interfered with the root to shoot translocation of Cu, Fe and Al (Al only estimated in Scots pine), but not with that of Zn and Mn. It is postulated that internal plant tolerance (promoted by P) plays a more important part in neutralizing toxic metal concentrations (Zn, and possibly also Fe) in the soil than do exclusion mechanisms. High applications of P without Cu may depress growth, as demonstrated for willow. Water-soluble soil P data may be misinterpreted if other limiting soil factors (pH, Cu status) have not been eliminated.     

锰毒及植物耐性机理研究进展

综述了近些年国内外关于锰毒及植物耐锰机理的研究成果,并指出了存在的问题和发展前景。锰毒是酸性土壤上限制作物产量的重要因子,国内外针对锰毒及植物耐受机制进行了相关研究,但进展较为缓慢。锰对植物的毒害效应体现在不同的细胞组织及生理生化水平上,不同植物耐受锰的机理也存在差异性,但大都集中在有机酸的螯合解毒、内部积累、外部排斥及氧化等方面。某些锰胁迫所诱导的基因也被筛选出来,并且部分生物学功能得以鉴定。此外,锰与其他营养元素间的协同或拮抗作用也得以阐述,伴随锰超富积植物-商陆在中国的发现,对锰毒及植物耐性机理的深入研究和探讨,将会对植物修复技术的开展产生理论和实践意义。     

Influence of heavy metal leaf contaminants on the in vitro growth of urban-tree phylloplane-fungi

The surfaces of urban woody vegetation are contaminated with varying amounts of numerous metallic compounds, including Cd, Cu, Mn, Al, Cr, Ni, Fe, Pb, Na, and Zn. To examine the possibility that these metals may affect phylloplane fungi, the above cations were tested in vitro for their ability to influence the growth of numerous saprophytic and parasitic fungi isolated from the leaves of London plane trees. Considerable variation in growth inhibition by the metals was observed. GenerallyAureobasidium pullulans, Epicoccum sp., andPhialophora verrucosa were relatively tolerant;Gnomonia platani, Cladsporium sp., andPleurophomella sp. were intermediate; andPestalotiopsis andChaetomium sp. were relatively sensitive to the incorporation of certain metals into solid and liquid media. If similar growth inhibitions occur in nature, competitive abilities or population structures of plant surface microbes may be altered by surface metal contamination. Metals causing the greatest and broadest spectrum growth suppression included Ni, Zn, Pb, Al, Fe, and Mn.