Plant Mn Concentrations Research Articles

The Effect of Manganese and Sulfur Applications on the Rocket (Eruca vesicaria subsp. Sativa) Plant Grown in Lime Soils

Due to the high lime and pH in the soil, sulfur and micro element deficiencies are observed in green vegetable plants. Rocket, one of the green vegetables and a member of the Brassicaceae family, is widely produced in our country. It is noteworthy that rocket is grown by producers almost everywhere and that this plant grown in our region also has a deficiency of microelements. For this reason, in this study were investigated that the sulfur and manganese requirement of rocket, which is one of the vegetable plants grown in Konya calcareous soil, and the effect of the interaction between these two elements on plant growth and yield. In our study, sulfur (S) fertilizer was applied in three doses (0- 40- 80 kg S da-1) and manganese (Mn) fertilizer in three doses (0- 1- 2 kg Mn da-1) was applied to the rocket plant. The experiment was carried out in the greenhouse conditions according to the randomized plots factorial design. At the end of the experiment, the average leaf height, chlorophyll SPAD value, plant fresh weight, plant height and plant Mn concentration did not differ with different doses of fertilizer applications in the rocket plant. On the other hand, the sulfur concentration in the plant and soil increased significantly with sulfur fertilization (p

The effect of phosphorus fertilizer under the influence of iron and zinc treatments on nutrient content and lettuce yield

Interaction between phosphorus (P), zinc (Zn), and iron (Fe) alters plant nutrient concentrations and nutritional quality. In this regard, there are a limited number of studies on P and micronutrient relations in lettuce plants. In this study, the effects of Zn and Fe applications on plant growth, concentrations, and contents of P, Zn, Fe, copper (Cu), and manganese (Mn) were determined in lettuce plants grown under increasing P rates. Lettuce plants grown under increasing P rates (0, 100, 200, and 400 mg kg−1 P) were treated with either sole or combined applications of 20 mg kg−1 Zn and 30 mg kg−1 Fe. Fresh and dry weights, P concentrations, and contents of lettuce were increased by P fertilization. With Zn and Fe applications, lettuce Fe contents were increased by medium P rates. Plant Zn contents were increased by P fertilization when the plant supplied Zn alone. Besides the highest P rate, Zn and Fe increased plant Zn content through P fertilization. Under no micronutrient condition, Cu concentration revealed insignificant changes, but its content was significantly increased by P application. Plant Mn concentration only increased by low P when the plant supplied Zn however Mn contents of lettuce were increased by P fertilization. In conclusion, even high P doses had no significant impact on Fe, Zn, Cu, and Mn concentrations in lettuce plants. Plant Zn concentrations increased when Zn was applied with Fe. Likewise, Cu increased but manganese declined. This emphasizes the importance of simultaneous Zn and Fe fertilizer application, especially in Zn biofortification research.

Manganese sources and rates impact plant Mn concentrations and soil Mn fractions

AbstractManganese (Mn) is an essential micronutrient for all organisms. In plants, Mn plays a critical role in photosynthesis and as a structural component of enzymes. In soils, Mn exists as different fractions of varying availability to plants. Mn fertilizers can be used to increase Mn availability to plants but are easily converted from a plant‐available fraction (exchangeable Mn) to an unavailable fraction (Mn‐oxides). Little research has been done in agricultural settings on soil Mn fractions; thus, the objective of this experiment was to study the effect of Mn additions on soil Mn fractions and plant Mn concentration. A greenhouse experiment was conducted by growing soybean (Glycine max) treated with three Mn application rates (recommended or 1×, 10×, and 50×) of two sources (MnSO4 and Mn ethylenediamine tetraacetic acid [MnEDTA]). Soil Mn fractions (Mehlich‐1 extractable, exchangeable, organic‐bound, Mn‐oxide, residual) were quantified via sequential Mn extraction procedures. Bioavailability was evaluated by measuring soybean leaf Mn concentrations. Both fertilizer types increased available soil Mn fractions. Leaf Mn concentration increased with MnSO4 50× application at the V3 stage and decreased with MnEDTA addition at the V3 and R2 stages. Mn additions likely resulted in the conversion of Mn into unavailable fractions. This was amplified by higher application rates, where total Mn increased by 18.5%, but available Mn decreased by 4.3% relative to initial soil values. Thus, our study showed that adding Mn to soils does not necessarily increase plant‐available Mn.

Alleviation of low phosphorus stress in Eucalyptus grandis by arbuscular mycorrhizal symbiosis and excess Mn

Tropical soils are highly-weathered acidic soils and frequently present two intersecting problems that can be detrimental to plant development: low phosphorus (P) and high manganese (Mn) availability. Mn can be phytotoxic, damaging the photosynthetic apparatus and/or competing with other nutrients. Eucalyptus grandis is often cultivated in such soil types and, despite being a tree generally tolerant to Mn excess, P deficiency may exacerbate toxicity. Arbuscular mycorrhizal (AM) fungi are known for their ability to provide P to the host plant in exchange of photosynthates. This symbiosis may also decrease Mn accumulation and overall alleviate metal stress. In a glasshouse experiment, E. grandis plants were grown for seven months in soil with low P availability adjusted to three Mn dose levels (control, 75 and 150 mg kg–1), with (AM) or without (NM) inoculation with Rhizophagus irregularis. We measured biomass, height, flavonoids (anthocyanin/flavonol) and chlorophyll indexes, chlorophyll a fluorescence parameters, AM colonization and Mn, P, Mg, K and Fe concentrations in shoots and roots. All plants presented low biomass production, and shoot P concentrations ranged from 0.13 to 0.52 g kg–1. Mn additions decreased mycorrhizal colonization, but no other negative impacts were seen in E. grandis, indicating that this species is relatively tolerant to excess Mn. At dose 75, shoots accumulated up to 2,000 mg Mn kg–1; however, this amount was not detrimental to most parameters, especially in NM plants, which had higher growth and Mg concentrations while presenting much lower flavonol and anthocyanin contents. At dose 150, plant Mn concentrations were similar to those at 75 Mn, despite higher soil availability, indicating that shoot concentrations around 2,000 mg kg–1 were a threshold for E. grandis under P deficiency. AM colonization intensity and arbuscule abundance were overall low, resulting in no improvements in P nutrition nor reduction of Mn uptake in high Mn treatments. However, AM symbiosis led to higher chlorophyll contents and non-photochemical quenching values, which are important in withstanding abiotic stress. Even though AM fungi inoculation did not improve P uptake, multivariate analysis suggests that the mycorrhizal pathway influenced nutrient acquisition in AM plants. Our results show that in E. grandis Mn excess had an alleviation and a hormetic effect, mitigating P deficiency stress rather than being phytotoxic. AM symbiosis did not improve mineral nutrition, despite providing some benefits involved in stress tolerance.

Effects of nitrogen addition on plant manganese nutrition in a temperate steppe

AbstractBackgroundManganese (Mn) is an essential nutrient for plant growth and a key factor driving litter decomposition. Nitrogen (N) deposition is expected to enhance soil Mn availability via soil acidification, and subsequently to increase plant Mn concentrations.AimsWe aimed to quantify the responses of Mn concentrations in green and senesced shoots at both species and community levels to N addition, and determine whether N addition would decrease Mn retranslocation efficiency during plant senescence.MethodsWe examined the changes of Mn concentrations in soil and in green and senesced shoots of all plant species across multiple N addition rates ranging from 0 to 50 g N m−2 y−1 in a temperate steppe after six years treatments. Plant Mn retranslocation efficiency were quantified at species, life form, and community levels. The relationship between plant Mn nutritional parameters and soil Mn availability across the N addition gradient was analyzed.ResultsThere were positive correlations between plant Mn concentrations and N addition rates for most species. Relative to the control plots, community‐level mean Mn concentration in green and senesced shoots in the plots received the highest level of N addition increased by 137.50% (from 0.19 mg kg−1 to 0.08 mg kg−1) and 187.50% (from 0.23 mg kg−1 to 0.08 mg kg−1), respectively. There was no correlation between Mn retranslocation efficiency and N addition rates at species, life form and community levels. Plant Mn status was weakly correlated with soil Mn concentrations for most species.ConclusionsPlant Mn retranslocation showed conserved responses to increasing N addition rates, which would be an adaptive strategy for plants in face of N‐induced higher soil Mn availability.

The use of mercapto-modified palygorskite prevents the bioaccumulation of cadmium in wheat

In this study, the mechanism by which mercapto-modified palygorskite (MPAL) mediates Cd and Mn absorption by wheat was elucidated. In the aqueous phase, MPAL can react with Cd to form Cd-thiol complexes and CdO and with Mn to form MnO. In the wheat-soil system, 0.1–0.3% MPAL application increased the biomass of wheat by 18.6–29.4% and decreased the Cd concentration in shoots and roots by 19.4–51.8% and 35.9–64%, respectively; however, MPAL application did not decrease the diethylenetriaminepentaacetic acid (DTPA)-extracted Cd concentration in soil, probably because the formed Cd-thiol complexes and CdO could not be taken up by plants but could be extracted by DTPA. MPAL appeared to increase the Mn concentration in plants and the DTPA-extracted Mn concentration in soil, possibly because of the reduction in soil Mn oxides to more soluble Mn(Ⅱ) by the thiol groups in MPAL. MPAL enriched plant growth-promoting rhizobacteria and Cd-immobilizing bacteria and strengthened the sulfate reduction metabolism in rhizosphere soil, which partly contributed to the improvement in plant growth and the reduction in Cd bioaccumulation in wheat. These findings highlight the importance of the thiol group in MPAL and the regulation of the rhizosphere bacterial community in mediating Cd and Mn bioaccumulation in wheat.

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.

Nutritional disorder in Pfaffia glomerata by mercury excess in nutrient solution

ABSTRACT: The mineral nutritional homeostasis in response to different concentrations of Hg (0, 25 and 50μM) was evaluated in Pfaffia glomerata plant. The exposure to the highest level of Hg (50µM) caused a decreasing in shoot and root fresh weights of 15.5% and 20%, respectively. Both shoot and root Hg concentrations increased linearly with increasing external Hg concentrations. Ca concentration decreased in shoot only at 50µM Hg, whereas shoot K and Mg concentrations decreased at both 25 and 50µM Hg, when compared to the control. A significant decrease in Cu, Zn, Fe and Mn concentrations in plants exposed to Hg was observed, but most Zn, Mn, and Cu in the roots. On the other hand, P concentration increased in both root and shoot of plants exposed at 25 and 50µM Hg, whereas Na concentration increased only in the root at 25 and 50µM Hg exposure. In general, tissue nutrient concentrations in P. glomerata plantlets exposed to Hg were significantly decreased, which indicates that the Hg may cause alteration on the mineral nutritional homeostasis of this species.

Reactivity and effectiveness of traditional and novel ligands for multi-micronutrient fertilization in a calcareous soil.

This study compares the effectiveness of multi-micronutrient formulations containing iron (Fe), manganese (Mn), and zinc (Zn) with traditional (EDTA, DTPA, HEEDTA, and EDDHAm) or novel chelates (o,p-EDDHA, S,S-EDDS, and IDHA) and natural complexing agents (gluconate and lignosulfonate). The stability and reactivity of the formulations were studied on batch experiments with calcareous soil and by speciation modeling. Formulations containing traditional ligands maintained higher Mn but lower Zn concentration in soil solution than the novel ligands. The gluconate and lignosulfonate maintained low concentrations of both Mn and Zn in soil solution. Selected formulations were applied into calcareous soil and their efficacy was evaluated in a pot experiment with soybean. The formulation containing DTPA led to the highest Zn concentration in plants, as well as the formulation containing S,S-EDDS in the short-term, which correlated with its biodegradability. The application of traditional or novel ligands in formulations did not result in sufficient plant Mn concentrations, which was related to the low Mn stability observed for all formulations under moderate oxidation conditions. The results highlight the need to consider the effect of metals and ligands interactions in multi-nutrient fertilization and the potential of S,S-EDDS to be used for Zn fertilization. Furthermore, it is necessary to explore new sources of Mn fertilization for calcareous soils that have greater stability and efficiency, or instead to use foliar fertilization.

Malate synthesis and secretion mediated by a manganese-enhanced malate dehydrogenase confers superior manganese tolerance in Stylosanthes guianensis.

Manganese (Mn) toxicity is a major constraint limiting plant growth on acidic soils. Superior Mn tolerance in Stylosanthes spp. has been well documented, but its molecular mechanisms remain largely unknown. In this study, superior Mn tolerance in Stylosanthes guianensis was confirmed, as reflected by a high Mn toxicity threshold. Furthermore, genetic variation of Mn tolerance was evaluated using two S. guianensis genotypes, which revealed that the Fine-stem genotype had higher Mn tolerance than the TPRC2001-1 genotype, as exhibited through less reduction in dry weight under excess Mn, and accompanied by lower internal Mn concentrations. Interestingly, Mn-stimulated increases in malate concentrations and exudation rates were observed only in the Fine-stem genotype. Proteomic analysis of Fine-stem roots revealed that S. guianensis Malate Dehydrogenase1 (SgMDH1) accumulated in response to Mn toxicity. Western-blot and quantitative PCR analyses showed that Mn toxicity resulted in increased SgMDH1 accumulation only in Fine-stem roots, but not in TPRC2001-1. The function of SgMDH1-mediated malate synthesis was verified through in vitro biochemical analysis of SgMDH1 activities against oxaloacetate, as well as in vivo increased malate concentrations in yeast (Saccharomyces cerevisiae), soybean (Glycine max) hairy roots, and Arabidopsis (Arabidopsis thaliana) with SgMDH1 overexpression. Furthermore, SgMDH1 overexpression conferred Mn tolerance in Arabidopsis, which was accompanied by increased malate exudation and reduced plant Mn concentrations, suggesting that secreted malate could alleviate Mn toxicity in plants. Taken together, we conclude that the superior Mn tolerance of S. guianensis is achieved by coordination of internal and external Mn detoxification through malate synthesis and exudation, which is regulated by SgMDH1 at both transcription and protein levels.

Phytoremediation potential of three aquatic macrophytes in manganese‐contaminated water

AbstractManganese (Mn) uptake capacities of water hyacinth (Eichhornia crassipes (Mart.) Solms, water lettuce (Pistia stratiotes L.) and slligator alternenthera (Alternanthera philoxeroides) were investigated with four Mn levels: 0(control), 50, 200, 400 mg/L. With increased Mn exposure, the tested plants showed similar responses with a decrease in relative growth rate and an increase in plant Mn concentrations. Comparatively, water lettuce had the significantly higher total Mn concentrations, shoots enrichment factor and translocation factor at all Mn‐treated treatments and the much greater total Mn removal at concentrations of 200 and 400 mg/L Mn. In most cases, Mn pollution significantly decreased Mg concentrations for all three plants. Concomitantly, increment trends of Fe, Cu and Zn concentrations were observed for water lettuce with the increasing external Mn concentrations, which could partly contribute to its higher Mn concentrations. The results indicated that water lettuce have standout potentials as a phytoremediation plant for Mn contaminated waters.

Manganese nutrition of pepper ( Capsicum annuum L.): Growth, Mn uptake and fruit disorder incidence

This research included two independent yet build up objectives: (i) to examine the effects of Mn concentration in the irrigation water on the yield and fruit quality of greenhouse-grown bell pepper exposed to heat stress; and (ii) to investigate in a laboratory experiment the role of Mn addition on oxidative and anti-oxidative components of fruit apoplast. The field experiment included four concentrations of Mn in the irrigation water (0, 0.2, 0.6 and 1.0 mg L −1). The effect of Mn application rate on vegetative growth and total fruit yield was insignificant and despite low Mn concentrations in zero-Mn-fed plants, no visible foliar Mn symptoms were observed. A quadratic regression was obtained between high-quality fruit yield and Mn concentration in fruit. Based on the quadratic equation, maximum high-quality yield was obtained when fruit-Mn concentration approached 44 mg kg −1 DW. The correlation also indicates that variations in high-quality yield could be explained by differences in fruit-Mn concentration. The combination of low-Mn nutrition and high air temperature which prevailed during the experiment (summer season) induced severe pale spots and blemished fruits; approximately 50% of fruits were infected in zero-Mn-fed plants. In a laboratory experiment with detached-fruit under high temperature the H 2O 2 concentration increased whereas ascorbic acid concentration decreased in the apoplast. In Mn-fed fruit the H 2O 2 concentration was attenuated and the activity of ascorbate oxidase was suppressed, with the result that apoplastic ascorbic acid concentration increased. In light of the known crucial role of Mn in enzyme activities and in detoxification of oxygen free-radicals, the pale spots might be related to Mn effect on oxidative stress-related apoplastic activities. The relationships between incidence of pale spots and plant-Mn concentration may support this hypothesis, but further research is needed to validate it.

Evaluation and correction of nutrient availability to Gerbera jamesonii H. Bolus in various compost-based growing media

Nutrient deficiencies usually constrain the use of some composted materials as peat-substitute growing media even if some fertilizer is applied to the media. In this work, we assessed the suitability of various composted materials as such or mixed with peat for potted plant production, with special emphasis on their effects on nutrient availability to plants. Further, we examined the effect of vivianite [Fe 3(PO 4) 2·8H 2O] as a fertilizer and its mixture with humic substances (HS) on these growing media (particularly their effectiveness in preventing Fe deficiency chlorosis in alkaline substrates). A completely randomized experiment design was developed involving the growth of gerber ( Gerbera jamesonii H. Bolus) and two factors, namely (i) the growing medium, specifically composted cork residue (C), compost obtained from a mixture of olive husk and cotton gin trash mixed with rice hulls and peat in a 1:1:1 volume proportion (OH), composted grape marc (GM), Sphagnum peat mixed with spent mushroom compost (M), coconut fibre (CF), and Sphagnum peat; and (ii) the Fe source (control without Fe, Fe-EDDHA, vivianite and vivianite + HS in a weight ratio of 10:1). The highest chlorophyll meter readings were provided by the two media with the lowest pH (peat and CF), and the lowest readings were provided by the medium exhibiting the highest pH (C). Composted grape marc (GM) and M provided the largest amounts of dry matter (DM), whereas peat and M gave the highest flower yields. Flower and DM yield were lower in CF and C than those in other substrates; the low production in the former can be ascribed to Ca deficiency; in fact, the medium was poor in this nutrient; therefore, plants grown on it exhibited low Ca concentration in leaves. On the other hand, the low chlorophyll meter readings and DM yield in C can be largely ascribed to Fe deficiency chlorosis since the application of Fe improved both the parameters, the best results being obtained with the vivianite + HS mixture. Vivianite-based treatments increased P concentrations in leaves, but only in more acidic medium (CF and peat), where the pH of the media facilitated the dissolution of the product. The adverse effects of Fe sources on the Mn and Zn concentrations in leaves were as a result of the antagonistic effect of the Fe supply, which varied with the particular growing medium: Fe-chelate depressed Mn in plants grown on C, whereas vivianite + HS decreased the Mn concentration in plants grown on GM. The results obtained with the different compost-based materials studied and the ability to overcome Fe deficiency in C by using a vivianite + HS mixture are interesting with a view to reduce the use of peat in the potted plant industry.

Iron‐Manganese Interaction in Chickpea as Affected by Foliar and Soil Application of Iron in a Calcareous Soil

Soil application of inorganic source of iron (Fe) is not effective in correction of Fe deficiency in calcareous soils. The chelate form of Fe is, therefore, used for that purpose. Application of Fe‐chelate, however, may reduce crop yields due to the reduction of some nutrients availability including manganese (Mn). A greenhouse experiment was conducted in a completely randomized design to study the effect of Fe and Mn on the dry matter yield (DMY), interaction of Fe‐Mn, and concentration and uptake of other nutrients in chickpea (Cicer arietinum L. var. Pars). Treatments consisted of three Mn levels as Mn SO4·4H2O and four Fe levels (Foliar and soil application of FeSO4·7H2O and Fe‐EDDHA, respectively). Results showed that both foliar and soil application of Fe decreased mean shoot DMY, but Mn addition had no significant effect. Foliar application of Fe and addition of Mn increased mean shoot Fe concentration and uptake. Soil application of Fe and Mn increased mean shoot copper (Cu) concentration and uptake. Mean shoot zinc (Zn) concentration or uptake was not affected by Fe or Mn. These results showed that the suppressing effect of Fe on plant Mn concentration was not due to the reduction in root: shoot ratio, dilution effect, Fe toxicity or reduction in Mn uptake by root. Therefore, it may be concluded that the antagonistic effect of Fe on the translocation of Mn from root to shoot is the main reason for reduction in shoot Mn concentration in chickpea.

Pigeonpea Response to Silicon, Phosphorus, and Rhizobium Inoculation in an Acid Coastal Plain Soil

ABSTRACT Pigeonpea [Cajanus cajan (L.) Millsp.] is a legume with potential as an alternative summer crop in the U.S. Southern Coastal Plain. It has low fertilizer and pesticide requirements, and is used for both animal feed and human food. Southern coastal plain soils are acidic and phosphorus (P) deficient before liming and fertilization. Under those conditions, pigeonpea is limited in its ability to symbiotically fix atmospheric nitrogen (N2). Calcium silicate application can reduce the adverse effects of soil acidity and also enhance the availability of P in such soils. The effects of calcium silicate on P availability and the effects of Rhizobium inoculation on the growth of pigeonpea on a Greenville soil from the coastal plain of Georgia were investigated in laboratory and greenhouse experiments. Both silicon (Si) and P applications significantly increased the growth of pigeonpea. Optimum fresh and dry shoot weights, plant-available water, shoot height, nitrogen (N) and P contents, and P:manganese (Mn) ratios were found when 1.96 g Si/pot (4.48 t Si/ha) was applied as calcium silicate. High levels of plant Mn concentrations were reduced by such application. Application of 0.1 g P/pot (39 kg P/ha) produced the optimum fresh and dry shoot weights, plant water content, and shoot height. Inoculation had no effect on plant growth. There were no interactions for growth among Si, P, and inoculation. Increased growth due to Si application was adduced to increased available N and P and reduced levels of Mn. Applied Si also increased plant-available water, which enhanced leaf erectness—an important factor in light interception and therefore in growth. Low soil-available P was increased by fertilizer P, resulting in increased growth. Although Si is not an essential element, calcium silicate improved the growth of pigeonpea grown on this low pH soil.

High fertigation frequency and phosphorus level: Effects on summer-grown bell pepper growth and blossom-end rot incidence

The objective was to examine the effects of fertigation frequency and P application rate on bell pepper growth and blossom-end rot (BER) incidence, under hot conditions. The experiment comprised six treatments: two concentrations of phosphorus (3 and 30 mg L−1) combined with three fertigation frequencies (two and eight events per day, and for 1.5 min every 25 min throughout the day). Increasing the fertigation frequency significantly increased the plants’ acquisition of nutrients, especially phosphorus and manganese. A significant linear regression was obtained between aboveground biomass, and leaf P concentration in the early vegetative stage. Based on the linear regression, 96% of the dry weight variations could be explained by differences in leaf P concentration, indicating that the main effect of fertigation frequency was related to improved P mobilization and uptake. Increasing the daily fertigation frequency from two to eight and to 30 applications reduced the number of BER fruits from 7 to 3 and to 2 per plant, respectively, and accordingly, increased the yield of export-quality fruits from 6.5 to 10 and to 10.5 per plant, respectively. The Mn concentration in plants exposed to low fertigation frequency were low, probably in the deficiency range, but they increased with increasing fertigation frequency. A negative correlation was found between the accumulated number of BER-affected fruits throughout the experiment and fruit-Mn concentrations. In light of recent findings that BER effects in the fruit tissue include the production of oxygen free-radicals and diminution of anti-oxidative compounds and enzymatic activities, and the known crucial role of manganese in enzyme activities and in detoxification of oxygen free-radicals, the relationships between BER incidence and fruit-Mn concentration may indicate that BER is related to Mn deficiency. Future researches are needed to validate this hypothesis.

The effect of manganese supply on exudation of carboxylates by roots of lucerne (Medicago sativa)

Some low-molecular-weight carboxylates commonly found in plant root exudates have the potential to increase the availability of Mn in the rhizosphere. Release of various compounds into the rhizosphere by plant roots may also be a mechanism by which certain species and genotypes are able to tolerate conditions of low Mn availability better than others. Lucerne (Medicago sativa L.) plants of Salado, a genotype tolerant to Mn deficiency, and Sirosal, an intolerant genotype, were grown in solution culture with 0, 5 or 500 nM Mn (Mn-0, Mn-5 and Mn-500). Exudates of whole root systems were collected at 14, 24 and 36 d and analysed by HPLC. Oxalate, tartarate, L-malate, lactate, malonate, maleate, citrate and succinate were detected and quantified in exudates under all Mn treatments. Malonate, citrate and succinate accounted for the majority of carboxylates in the exudates. Exudation increased with plant age, but amounts of individual carboxylates remained constant in proportion to the total amount exuded. A significant increase in exudation of all carboxylates other than malonate and maleate resulted from omission of Mn from nutrient solutions. Salado exuded more oxalate, tartarate, L-malate, lactate, citrate and succinate than Sirosal at Mn-0, and more citrate and succinate than Sirosal at Mn-5. Genotypic differences in carboxylate exudation under Mn-0 were associated with production of roots with diameter <100 μm. Plant Mn concentrations and growth rates suggested carboxylate exudation differences were not the sole factor responsible for differential tolerance to Mn deficiency in the lucerne genotypes.

Predicting Zn and Cu status in cereals – potential for a multiple regression model using soil parameters

Prediction of micronutrient deficiency normally involves soil extraction tests and correlations between soil extractable micronutrients and their concentration in plant tissues. The present study reports that the inclusion of soil properties in addition to soil extraction data represents a powerful tool for improving models for a simple determination of phytoavailable Zn and Cu. Soil and plant samples were collected in spring 2000 from 19 cereal fields in Central and Southeast Norway at sites with known micronutrient deficiency. Based on the sample information, the model approach used stepwise regression, applying actual plant Zn and Cu concentration as the response, and soil extractable Zn/Cu and physico-chemical properties of the soil as model predictors. A model involving citric acid extractable Zn coupled with selected soil properties could predict the concentration of Zn in plant tissues of barley and oats grown under field conditions with a significantly high precision (R2=0·96, P&lt;0·001). The soil parameters included in the model, and their importance for phytoavailability of Zn, were in the order: citric acid extractable Zn&gt;clay content&gt;total Zn&gt;pH&gt;total C&gt;total N. Inclusion of DTPA extractable Zn in the model, rather than citric acid, resulted in a slightly lower precision in the prediction of phytoavailable Zn (R2=0·86, P&lt;0·001). A corresponding model for phytoavailable Cu, determined by DTPA and soil parameters, gave less precise prediction (R2=0·59, P&lt;0·01). DTPA was more suitable for predicting phytoavailable Cu than citric acid. Plant Mn concentration could not be correlated to any of the extracting agents.

Ameliorating acid soils with organic materials: effects of amendments derived from coal on yield and composition of young wheat plants grown on an acid red podzol

Acidity in surface and subsurface soil horizons limits crop and pasture production over considerable areas of the world, and lime is the traditional amendment used to neutralize surface soil acidity. Earlier reports have indicated that calcium (Ca)‐saturated organic materials, produced by the oxidation of coal, may be of value as ameliorants for subsurface acidity. Two of them (OXPR and OXFU) were evaluated and compared with lime in pot studies with wheat (Triticum aestivum). In the first experiment, lime, OXPR and OXFU, each at four rates, were applied to an acid red podzolic soil, high in extractable aluminum (Al) and were compared for their ability to improve seedling root growth. In the second experiment, the three amendments were applied to the same soil and shoot yields and mineral content were measured after five weeks growth. The three amendments raised soil pH, lowered extractable Al and increased root elongation. OXFU at the highest rate (251 ha‐1) inhibited root growth possibly due to the high concentration of solutes as indicated by high electrical conductivity of the soil solution. In the second experiment the three amendments improved shoot yields, with significant increases up to 0.81 Ca ha‐1 application. Yields were in general higher with lime than with OXPR and OXFU at equivalent rates of added Ca. However, a significant asymptotic relationship was observed between yield and calcium carbonate (CaCO3) equivalence of each of the applied amendments. Yield was highly correlated with measures of soil Al {r2 for [Al] in 0.01M calcium chloride (CaCl2), 0.915; [Al] in 0.1M barium chloride (BaCl2)/ammonium chloride (NH4C1), 0.873; [Al] in water, 0.779; [Al] in water/EC, 0.904}. Plant manganese (Mn) concentrations were decreased by lime and OXPR and there were linear correlations between plant Mn concentration and soil Mn extractable in 0.01 M CaCl2 With OXFU, which has a high concentration of water soluble Mn, plant Mn was decreased below the unamended controls only at the higher rates of application. .Leaf tissue zinc (Zn) concentrations were high in treatments receiving the two coal‐derived amendments. In an effort to determine the role of ion complexation in the remediation process, a third study evaluating the Al complexing ability of the two coal derived products was compared to that of a water‐soluble fraction extracted from chestnut (Castanea saliva) litter which is known to have a high affinity for Al. The two coal derived materials had considerably lower affinities for Al than the chestnut extract supporting the thesis that complexing reactions were of minor importance in the observed responses. The results indicate that field testing of these products is warranted particularly at sites where plant growth is constrained by subsurface soil acidity.

Manganese retention by selected calcareous soils as related to soil properties1

Calcareous soils often need supplemental manganese (Mn) to support optimum plant growth, but some reports show that the apparent recovery of applied Mn is very low in such soils, i.e., nearly all of the applied Mn is retained in the soil. This experiment was conducted to find the relationship between the retained Mn and selected properties of calcareous soils. Eleven surface (0–20 cm) soil samples with pH ranging from 7.7 to 8.1 and calcium carbonate equivalent (CCE) ranging from 20 to 50% were used in the Mn adsorption study. Two‐gram subsamples of each soil were equilibrated with 20 mL of 0.01M CaCl2 solutions initially containing 10 to 200 mg Mn L‐1. The Mn that disappeared from solution (after 6 h shaking at 25°C) was considered as adsorbed (retained) Mn. The adsorption data showed a highly significant fit to Freundlich and also to the two‐surface Langmuir adsorption isotherms. The coefficients of both isotherms showed significant positive correlations with cation exchange capacity (CEC), organic matter (OM), and CCE of the soils indicating that OM and calcium carbonate are the sites of Mn retention in calcareous soils. Comparison of the adsorption data of this experiment with those of plant Mn uptake of the same soils (published earlier) shows that as the Langmuir second surface adsorption maxima (maximum retention capacity) of the soils increase the plant Mn concentration and uptake decrease.