Effect of nitrogen forms on reduction of manganese oxides in an Oxisol by plant root exudates

Reductive dissolution of soil manganese (Mn) oxides increases potential toxicity of Mn²⁺ to plants. In order to examine the effect of nitrogen forms on reduction of Mn oxides in rhizosphere soil, a rhizobox experiment was employed to investigate the reduction of Mn oxides due to the growth of soybean and maize in an Oxisol with various contents of NO₃^–-N and NH₄⁺-N and a total N of 200 mg kg^?1. The results showed that exchangeable Mn²⁺ in rhizosphere soil was 9.6–32.7 mg kg^?1 higher than that in bulk soil after cultivation of soybean and maize for 80 days, which suggested that plant root exudates increased reduction of soil Mn oxides. Application of ammonium-N promoted reduction of Mn oxides in rhizosphere soil compared to application of nitrate and nitrate together with ammonium. Soybean cultivation led to a higher reduction in soil Mn oxides than maize cultivation. Application of single ammonium enhanced Mn uptake by the plants and led to more Mn accumulating in plant leaves, especially for soybean. Therefore, application of ammonium-based fertilizer can promote reduction of soil Mn oxides, while application of nitrate-based fertilizer can inhibit reduction of soil Mn oxides and thus reduce Mn²⁺ toxicity to plants.     

Fractionation and Speciation of Manganese in Rhizosphere Soils of Pseudomonas sp. Rhizobacteria Inoculated Pistachio (Pistacia vera L.) Seedlings Under Salinity Stress

Enhancement of manganese (Mn) availability in saline and Mn-deficient soils is very important for plant growth. An experiment was carried out to evaluate the effect of Pseudomonas sp. rhizobacteria (P₀ (control), P₁, P₂ and P₃) and Mn (0 and 10 mg Mn kg^?1 soil) on the distribution of Mn in the rhizosphere of pistachio seedlings under salinity stress (0, 1000 and 2000 mg NaCl kg^?1 soil). The results showed that salinity decreased the dry weight, Mn uptake and chlorophyll content of the pistachio seedlings. However, inoculation with rhizobacteria increased these parameters in saline conditions. Application of rhizobacteria increased the availability of Mn in the rhizosphere soil. The use of rhizobacteria decreased the residual-Mn form in the rhizosphere. Inoculation with rhizobacteria increased the percent of Mn²⁺ and MnCl⁺ species in the soil solution. However, pistachio seedlings inoculation with rhizobacteria increased the contents of Mn available forms in the rhizosphere soil.     

Manganese efficiency and maganese‐uptake kinetics of raya (Brassica juncea), wheat (Triticum aestivum), and oat (Avena sativa) grown in nutrient solution and soil

Manganese (Mn) deficiency is reported worldwide and often decreases crop yield. However, plant species differ in their susceptibility to Mn deficiency. Poaceae are often inefficient, whereas Brassicaceae seem to be efficient in Mn uptake. The objective of this paper was to determine the relevance of Mn‐uptake kinetics, root‐system size, and Mn mobilization for differences in Mn efficiency of wheat, oat, and raya. To determine Mn‐uptake kinetics, wheat (Triticum aestivum L. cv. PBW 343), raya (Brassica juncea L. cv. RLM 619), and oat (Avena sativa L. cv. Aragon) were grown in a growth chamber together in complete nutrient solution having an average Mn concentration of 90, 180, 360, 910, and 2270 nmol L^–1. For determining Mn efficiency of the three species in soil, the plants were grown for 22 d in pots filled with 3 kg of a loamy soil low in Mn availability (pH (CaCl₂) 7.4; DTPA‐extractable Mn: 3.5 mg (kg soil)^–1). The soil was fertilized with 0, 1, 2, 4, and 8 mmol Mn (kg soil)^–1 resulting in Mn soil‐solution concentrations ranging from 40 to 90 nmol L^–1, hence lower than in the solution experiment. In order to determine Mn soil‐solution concentration close to the root surface, the root length density was increased by growing two plants of raya and four plants of wheat in only 250 mL soil columns for 25 d. In solution culture at high concentrations, raya showed a higher Mn uptake compared to wheat and oat. However, at low Mn supply, all three species were comparably Mn‐efficient, i.e., plant growth was similar, and also the uptake was similar. In soil, the highest yield was achieved for raya in the unfertilized treatment whereas the Poaceae needed at least a fertilization of 1 mmol Mn (kg soil)^–1. The Poaceae showed a yield reduction of about 40% in the unfertilized treatment. Manganese concentration in the shoot dry weight was always higher in raya than in wheat or oat. This was due to a higher Mn uptake whereas relative shoot‐growth rate and root‐to‐shoot ratio were similar among the species. The higher Mn uptake of raya in soil was in contradiction to the comparable Mn‐uptake kinetics of the three crops at low Mn concentration in solution. This points to plant differences in their ability to affect Mn availability in the rhizosphere. In the bulk soil, all the crops decreased Mn solution concentration, but this effect was somewhat less for raya. But in the rhizosphere, raya increased Mn soil‐solution concentration significantly to 58 nmol L^–1, as compared to 37 nmol L^–1 of the unplanted control soil. In contrast, wheat showed a Mn solution concentration of 25 nmol L^–1 which was not significantly different from the control. The results indicate that differences in Mn efficiency among the crops studied are related to their ability to affect the solubility of Mn in the rhizosphere.     

Estimation of plant available manganese in acidic subsoil horizons

Abstract

General agreement does not exist as to the most appropriate method to estimate plant available Mn in soils. In the current investigation soil and soil solution Mn were measured in limed and unlimed treatments of 11 acidic subsoil horizons and related to plant Mn concentrations, Mn uptake and growth of subterranean clover (Trifolium subterraneum L. cv. Mt. Barker) and switchgrass (Panicum virgatum cv. Cave‐in‐Rock). Manganese measurements were taken at planting and harvest and included: Mn extracted by 1M NH₄OAc (pH 7), 0.01M CaCl₂, 0.05M CaCl₂, 0.033M H₃PO₄, 0.005M DTPA, 0.2% hydroquinone in 1M NH₄OAc (pH 7), 0.01M NH₂ OH.HCl 4 2 in 0.01M HNO₃, total soil solution Mn and concentrations and 2+ activities of Mn²⁺ calculated from the GEOCHEM program. Measured and calculated values of soil solution Mn generally gave the best correlations with subterranean clover and switchgrass Mn concentrations and Mn uptake. Root Mn concentrations were highly correlated with soil solution Mn measurements taken at harvest with r=0.97 and r=0.95 (p<0.01) for subterranean clover and switchgrass respectively. The Mn extracted by 0.01M CaCl was also significantly correlated (p<0.01) with plant Mn concentrations and Mn uptake and proved to be better than the other extractants in estimating plant available Mn. Although Mn concentrations as high as 1769 mg/kg (shoots) and 8489 rag/kg (roots) were found in subterranean clover, Mn did not appear to be the major factor limiting growth. Measures of soil and soil solution Mn were not strongly correlated with yield. Both Al toxicities and Ca deficiencies seemed to be more important than Mn toxicities in limiting growth of subterranean clover and switchgrass in these horizons.     

Relative effectiveness of manganese sulfate and manganous oxide applied on organic soil

Abstract

The relative effectiveness of MnSO₄ (10 and 200 mesh) and MnO (8, 200 and 325 mesh) used in organic soil application was evaluated by plant growth, Mn concentration, Mn uptake and yield of Acme soybeans and Downing Yellow Globe onions.

The 10 mesh MnSO₄ was superior to all other materials, while the 8 mesh Mn was less effective than any other material. Intermediate effectiveness was obtained from 200 mesh MnSO₄ and 200 or 325 mesh MnO.     

Effect of soil heating on the dynamics of soil available nutrients in the rhizosphere

The effect of soil heating on the dynamics of soil available nutrients in the rhizosphere was evaluated. A pot experiment was carried out by using a rhizobox; a pot which enables to sample soils and soil solutions not only temporally with plant growth but also spatially depending on the distance from the root-accumulating compartment. The experiment consisted of 4 treatments; soils with or without heating treatment (150°C, 3 h), each of which was either planted with maize (Zea mays L.) or not. During the 17-d experiment, soil solutions at 0–2 mm from the root-accumulating compartment were collected 5 times. Soils depending on the distance from the root-accumulating compartment and plants were also collected after the experiment. The ionic concentrations of the soil solutions and soil water extracts, and the nutrient contents of plants were analyzed. Immediately after soil heating, the concentrations of cations, SO₄ ^2-, CI^-, water-soluble P, and water-soluble organic carbon increased significantly. With plant growth, the total ionic concentration in the rhizosphere soil solution increased for heated soil, whereas it decreased for unheated soil. The increase of the concentrations of cations and SO₄ ^2- in the rhizosphere of heated soil was appreciable, suggesting that the movement of cations such as Ca²⁺ and Mg²⁺ by mass flow was regulated by that of SO₄ ^2-. Moreover soil heating inhibited nitrification, resulting in the supply of N mainly in the form of NH₄ ⁺ within 10 mm from the root-accumulating compartment. As a result, the soil pH decreased in the rhizosphere of heated soil. The amount of nutrients absorbed by plants, on the other hand, did not change significantly by soil heating except for an increase of P uptake. The increase of P uptake could be explained not only by the immediate increase of the water-soluble P concentration but also by the dissolution of Ca-bound P and the hydrolysis of water-soluble organic P in the rhizosphere.     

Response of wheat seedlings to Mn‐lignosulfonate adhered to granular NPK

Manganese (Mn) deficiency is a widespread crop micronutrient disorder. The aim of this work was to evaluate two NPK fertilizers coated with Mn that eliminate the specific labor cost for applying Mn and that allow the correction of Mn deficiency in wheat (Triticum aestivum L.). Two Mn sources [MnSO₄ and Mn‐lignosulfonate (MnLS)] were compared as NPK coatings at doses of 0.1, 0.3, and 1.0% (w/w) in hydroponic, perlite, and soil pot cultures under growth chamber and greenhouse conditions with wheat to evaluate the effects on dry matter production and Mn concentrations. For the NPK+MnLS product, 52–63% of the total Mn remained in solution at calcareous conditions. However, the NPK+MnSO₄ product was able to maintain only 14–25% of the total Mn added in solution. As expected, the MnLS product resulted in higher Mn concentrations in shoots than the MnSO₄ product due to the Mn complexation by lignosulfonate which preserved Mn from precipitation and maintained it available for plants. In the experiment with perlite as growth substrate, at low Mn dose (0.1% Mn) a similar Mn concentration in wheat shoots was found (57 mg kg^?1 DW for the MnSO₄ coating versus 72 mg kg^?1 DW for MnLS coating), but at the highest dose (1.0% Mn) the NPK+MnLS showed a significant increase in shoot Mn concentration (167 versus 132 mg kg^?1 DW). Soil application of coated NPK products showed similar Mn concentrations in shoots with both Mn sources (29–37 mg kg^?1 DW), except for the NPK+MnSO₄ (0.1%) treatment (only 18 mg kg^?1 DW). Based on the recommended Fe/Mn values (Fe : Mn ratio = 1.5–2.5) given in the literature for plants with a correct nutrition, only the NPK+MnLS (0.3%) fulfilled this ratio (Fe : Mn = 2.5).     

Root-induced changes in the rhizosphere: Importance for the mineral nutrition of plants

Root-induced changes in the rhizosphere may affect mineral nutrition of plants in various ways. Examples for this are changes in rhizosphere pH in response to the source of nitrogen (NH₄-N versus NO₃-N), and iron and phosphorus deficiency. These pH changes can readily be demonstrated by infiltration of the soil with agar containing a pH indicator. The rhizosphere pH may be as much as 2 units higher or lower than the pH of the bulk soil. Also along the roots distinct differences in rhizosphere pH exist. In response to iron deficiency most plant species in their apical root zones increase the rate of H⁺ net excretion (acidification), the reducing capacity, the rate of Fe^III reduction and iron uptake. Also manganese reduction and uptake is increased several-fold, leading to high manganese concentrations in iron deficient plants. Low-molecular-weight root exudates may enhance mobilization of mineral nutrients in the rhizosphere. In response to iron deficiency, roots of grass species release non-proteinogenic amino acids (?phytosiderophores”?) which dissolve inorganic iron compounds by chelation of Fe^III and also mediate the plasma membrane transport of this chelated iron into the roots. A particular mechanism of mobilization of phosphorus in the rhizosphere exists in white lupin (Lupinus albus L.). In this species, phosphorus deficiency induces the formation of so-called proteoid roots. In these root zones sparingly soluble iron and aluminium phosphates are mobilized by the exudation of chelating substances (probably citrate), net excretion of H⁺ and increase in the reducing capacity. In mixed culture with white lupin, phosphorus uptake per unit root length of wheat (Triticum aestivum L.) plants from a soil low in available P is increased, indicating that wheat can take up phosphorus mobilized in the proteoid root zones of lupin. At the rhizoplane and in the root (root homogenates) of several plant species grown in different soils, of the total number of bacteria less than 1 % are N₂-fixing (diazotrophe) bacteria, mainly Enterobacter and Klebsiella. The proportion of the diazotroph bacteria is higher in the rhizosphere soil. This discrimination of diazotroph bacteria in the rhizosphere is increased with foliar application of combined nitrogen. Inoculation with the diazotroph bacteria Azospirillum increases root length and enhances formation of lateral roots and root hairs similarly as does application of auxin (IAA). Thus rhizosphere bacteria such as Azospirillum may affect mineral nutrition and plant growth indirectly rather than by supply of nitrogen.     

接种AM真菌对采煤沉陷区文冠果生长及土壤特性的影响

煤炭井工开采往往造成地表塌陷,导致了土壤养分贫瘠和水分缺乏,土壤沙化和水土流失,从而限制了当地矿区植被生长,而丛枝菌根真菌(arbuscular mycorrhiza fungi,AM真菌)对植被生长有促进作用。以文冠果为宿主植物,采用野外原位监测和室内分析方法,研究了未接种和接种丛枝菌根真菌对采煤沉陷区复垦植物文冠果生长和土壤特性的影响。结果表明:与未接种AM真菌处理相比,接种AM真菌显著提高了文冠果根系菌根侵染率和土壤根外菌丝密度,7月接种AM真菌文冠果的株高、冠幅和地径提高了31.89%,23.07%,9.89%。同时,9月接种AM真菌处理的根际土壤全氮、碱解氮和有机碳含量分别比对照组增加0.29g/kg、13.0mg/kg和1.4g/kg,接种AM真菌显著提高了根际土壤的含水率、总球囊霉素和易提取球囊霉素,而速效磷和速效钾的含量显著降低。相关分析结果表明,菌根侵染率、土壤根外菌丝密度与根际土壤理化性质之间存在协同反馈效应。因此,接种AM真菌促进了采煤沉陷区复垦植被文冠果的生长和土壤的改良,这对矿区水土保持、维持生态系统稳定性和持续性具有重要意义。     

Effects of lime and applied Mn on plant Mn,growth and chlorophyll concentration of ‘Tifway II’ bermudagrass

Abstract

A glasshouse study was conducted to determine effects of lime and Mn applied to three Florida soils on plant Mn, growth, and chlorophyll concentration of ‘Tifway II’ bermudagrass (Cynodon dactylon x Cynodon transvaalensis). Four replications of three lime rates (0, 1000, and 2000 mg CaCO₃/kg as dolomite and Ca(OH)₂ for Astatula fine sand (Typic Quartzipsamment, hyperthermic, uncoated) and Pompano fine sand (Typic Psammaquent, siliceous, hyperthermic); 0, 2000, and 4000 mg CaCO₃/kg as dolomite and Ca(OH)₂ for Myakka fine sand (Aeric Haplaquod, sandy siliceous, hyperthermic) and three Mn applications (none, 10 mg Mn/kg as MnSO₄, and 5 mg Mn/kg as MnEDTA) were used in a randomized, complete block, factorial design. A wide range of plant Mn concentrations existed across treatments for each soil. Differences in plant Mn concentration did not cause significant differences in growth or chlorophyll concentration. The critical plant Mn concentration was not reached, but it appeared to be below 20 mg Mn kg for bermudagrass. Models for prediction of plant Mn concentration using soil pH and extractable soil Mn (Mehlich I, Mehlich II, DTPA‐TEA) were obtained. The applications of MnSO, and MnEDTA each resulted in increased plant Mn under acidic soil conditions. Neither Mn application resulted in increased plant Mn concentration in grass grown on Pompano fine sand with soil pH values of 7.0 or above.     

石灰性土壤中锰素营养的研究——Ⅱ.土壤有效锰的测定

自从Leeper^[5]首先提出用对苯二酚提取土壤易还原态锰评价土壤供锰状况以来,四十多年间各国的土壤农化工作者陆续设计并使用了种类繁多的土壤有效锰的提取剂。将其归纳大致可分为五类。     

Evaluation of manganese inorganic fertilizer sources and Mehlich‐3 extractant for prediction of manganese deficiency in soybeans on a Sharkey silty clay

Abstract

A greenhouse experiment was conducted on two Sharkey silty clay (very fine, montmorillonitic, nonacid, thermic, Vertic Haplaquept) soils (SharkeyA and‐B) to compare MnSO₄ and two Mn‐oxysulfatc sources (oxysulfate‐A and‐B) and to evaluate the Mehlich‐3 extractant. Soils were collected from a soybean [Glycine max (L.) Merr.] field with (Sharkey‐A) and without (Sharkey‐B) a history of Mn deficiency symptoms. Treatments consisted of two lime treatments, O and 2000 mg kg^‐1, and three Mn rates, 0, 20, and 40 mg kg^‐1. Each source was broadcast in granular form. Manganese sulfate was also applied in solution. Soybean plants were grown for 40 days. Dry weight, whole‐plant Mn concentration, and total Mn uptake were measured. Extractable soil Mn was determined using the Mehlich‐3 extractant. Dry weight was increased by applied Mn only on the Sharkey‐A soil, especially for the limed treatment. The Mehlich‐3 extractant delineated between the responsive (2.3 mg Mn kg^‐1) and non‐responsive (6.0 mg Mn kg^‐1) Sharkey soils. On the limed Sharkey‐A soil, sulfate applied in the granular form was more effective than sulfate applied in solution. It was also more effective than the oxysulfate sources, and the oxysulfate‐A was superior to the oxysulfate‐B source. Whole‐plant Mn concentration and uptake followed trends similar to those observed with dry weight, particularly on the Sharkey‐A soil. Multiple regression analyses suggested that soil pH, along with Mehlich‐3 extractable Mn, may improve the Mn soil test interpretation.     

Effect of Free Manganese Activity on Yield and Uptake of Micronutrient Cations by Barley and Oat grown in Chelator-buffered Nutrient Solution

The uptake of micronutrient cations in relation to varying activities of Mn²⁺ was studied for barley (Hordeum vulgare L. var. Thule) and oat (Avena sativa L. var. Biri) grown in chelator buffered nutrient solution. Free activities of Mn²⁺ were calculated by using the chemical speciation programme GEOCHEM-PC. Manganese deficient conditions induced elevated concentrations of Zn and Fe in shoots of both species. The corresponding antagonistic relationship between Mn and Cu could only be seen in barley. The observed antagonistic relationships were only valid as long as the plant growth was limited by Mn deficiency. The Mn concentration in both plant species increased significantly with increasing Mn²⁺ activity in the nutrient solution. The concentration of Mn in the shoots of oat was higher than for barley except under severe Mn deficiency where it was found equal for both species. Manganese was accumulated in the roots of barley at high Mn²⁺ activity. The different shoot concentrations of Mn between barley and oat are therefore attributed to the extent of Mn translocation from roots to shoots. Manganese deficiency induced a significant increase in the shoot to root ratio in both species.     

Consequences of sodium exclusion for the osmotic potential in the rhizosphere – Comparison of two maize cultivars differing in Na+ uptake

According to the biphasic model of growth response to salinity, growth is first reduced by a decrease in the soil osmotic potential (Ψ_o), i.e., growth reduction is an effect of salt outside rather than inside the plant, and genotypes differing in salt resistance respond identically in this first phase. However, if genotypes differ in Na⁺ uptake as it has been described for the two maize cultivars Pioneer 3906 and Across 8023, this should result in differences in Na⁺ concentrations in the rhizosphere soil solution and thus in the concentration of salt outside the plant. It was the aim of the present investigation to test this hypothesis and to investigate the effect of such potential differences in soil Ψ_o caused by Na⁺ exclusion on plant water relations. Sodium exclusion at the root surface of intact plants growing in soil was investigated by sampling soil solution from the rhizosphere of two maize cultivars (Across 8023, Pioneer 3906). Plants were grown in a model system, consisting of a root compartment separated from the bulk soil compartment by a nylon net (30 μm mesh size), which enabled independent measurements of the change of soil solution composition and soil water content with increasing distance from the root surface (nylon net). Across 8023 accumulated higher amounts of sodium in the shoot compared to the excluder (Pioneer 3906). The lower Na⁺ uptake in the excluder was partly compensated by higher K⁺ uptake. Pioneer 3906 not only excluded sodium from the shoot but also restricted sodium uptake more efficiently from roots relative to Across 8023. This was reflected by higher Na⁺ concentrations in the rhizosphere soil solution of the excluder 34 days after planting (DAP). The difference in Na⁺ concentration in rhizosphere soil solution between cultivars was neither due to differences in transpiration and thus in mass flow, nor due to differences in actual soil water content. As the lower Na⁺ uptake of the excluder (Pioneer 3906) was only partly compensated by increased uptake of K⁺, soil Ψ_o in the rhizosphere of the excluder was more negative compared to Across 8023. However, no significant negative effect of decreased soil Ψ_o on plant water relations (transpiration rate, leaf Ψ_o, leaf water potential, leaf area) could be detected. This may be explained by the fact that significant differences in soil Ψ_o between the two cultivars occurred only towards the end of the experiment (27 DAP, 34 DAP).     

Phylogenetic positions of Mn<Superscript>2+</Superscript>-oxidizing bacteria and fungi isolated from Mn nodules in rice field subsoils

We isolated manganous ion (Mn²⁺) oxidizing bacteria and fungi from Mn nodules collected from two Japanese rice fields. The phylogenetic position of the Mn-oxidizing bacteria and fungi was determined based on their 16S rDNA and 18S rDNA sequences, respectively. Among 39 bacterial and 25 fungal isolates, Burkholderia and Acremonium strains were the most common and dominant Mn²⁺-oxidizing bacteria and fungi, respectively. Majority of the Mn-oxidizing bacteria and fungi isolated from the Mn nodules belonged to the genera that had been isolated earlier from various environments. Manganese oxide depositions on Mn²⁺-containing agar media by these microorganisms proceeded after their colony developments, indicating that the energy produced from Mn²⁺ oxidation is poorly used for microbial growth.     

Uptake and distribution of manganese applied to leaves of Vicia faba (cv. Herzfreya) and Zea mays (cv. Regent) plants

Uptake and transport of Mn applied to leaves was studied in maize (Zea mays cv. Regent) and horse bean (Vicia faba cv. Herzfreya), two important crops in Egypt. Under controlled conditions in a growth chamber, maize and horse bean plants were grown in solution culture without Mn. After 20 days, Mn was applied to one older leaf by submerging part of the leaf blade into 0.1 mM MnSO₄ or MnEDTA solution for 48 h. At harvest (24 h later), plants were divided into fractions and Mn concentrations and contents determined. Plants without Mn application served as control. Only 1% of the Mn supply was taken up. Most of it remained at the application zone. However, part of the Mn moved out of the leaf of application and was preferentially transported to the shoot apex. This was indicated by a up to 2 times higher Mn concentration of the youngest leaf. When Mn was applied as MnEDTA, Mn uptake was lower but translocation enhanced compared to MnSO₄. There were no consistent differences between the plant species although mobility of Mn seemed to be higher in maize. Although the amounts of Mn taken up and translocated were low, the results suggest that in these plant species, leaf-applied Mn may contribute to the Mn nutrition of new growth.     

Mechanism of manganese toxictty and tolerance of plants VII. effect of light intensity on manganese‐induced chlorosis

Effect of light intensity on Mn‐induced chlorosiss was investigated with bush bean (Phaseolus vulgaris L.) and corn (Zea mays L.) seedlings. The seedlings were grown in nutrient solutions containing different concentrations of Mn in enclosures which transmitted different percentages of the total solar radiation. At high levels of Mn in nutrient solution, the increase in light intensity increased the Mn uptake by the plant and resulted in a decrease in the chlorophyll content of the leaves. Even at similar levels of Mn concentrations within the leaves, high light intensity increased the severity of Mn‐induced chlorosis.

Photobleaching experiments were carried out with isolated chloroplasts suspended in media containing 0, 10^‐4 , 10^‐3,10^‐2 and 10^‐1 M Mn²⁺. Addition of Mn²⁺ to the medium decreased the extent of photobleacing of chlorophyll with increaing Mn²⁺ concentration up to 10^‐3 M . In concentrations of Mn²⁺ higher than 10^‐3 M, the extent of bleaching was increased again, accompanied by precipitation of oxidized manganese in the medium.

It is suggested that high light intensity stimulates not only the Mn uptake by the plant but also the destruction of chlorophyll when Mn in excess.     

苗期干旱胁迫下施氮对玉米氮素吸收和土壤生物化学性质的影响

研究苗期干旱胁迫下施氮对东北春玉米氮素吸收利用和土壤生物化学性质的影响,为区域玉米养分管理与逆境调控提供依据.研究设置水、氮二因素盆栽试验,土壤水分包括3个水平:田间持水量的30％(W0),50％(W1)和70％(W2);施氮量包括2个水平:不施氮(N0)和施氮0.24 g/kg(N1),测定不同水氮条件下玉米苗期的植...     

Inoculation of ‘Golden Delicious’ Apple Trees on M9 Rootstock with Azotobacter Improves Nutrient Uptake and Growth Indices

ABSTRACT

Roots of young ‘Golden Delicious’ apple on M9 rootstock were inoculated with four strains of Azotobacter chroococcum, which were isolated from various soils. Effects of these strains in combination with different levels of nitrogen (N) fertilizer and compost on plant growth and nutrient uptake were studied over two seasons. Therefore, a factorial arrangement included four strains of A. chroococcum, two levels of N-fertilizer (0 and 35 mg N kg^?1soil of ammonium nitrate) and two levels of compost (0 and 12 g kg^?1 soil of air-dried vermicompost). Among the four strains, AFA₁₄₆ was the most beneficial strain, as it increased leaf area, leaf potassium (K), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), and boron (B) uptake and root N, phosphorus (P), potassium (K), Mn, and Zn. The combination of AFA₁₄₆ strain, compost and N fertilizer increased leaf uptake of Ca, Mg, Fe, Mn, Zn, and B, and root uptake of P, K, Ca, Mg, Mn, and copper (Cu), and root dry weight.