Manganese uptake and Mn efficiency of wheat cultivars are related to Mn‐uptake kinetics and root growth

Wheat cultivars differ widely in manganese (Mn) efficiency. To investigate the reasons for different Mn efficiencies, a pot experiment with soil, a solution‐culture experiment, and model calculations were carried out. The pot experiment was conducted with wheat (Triticum aestivum L. cvs. PBW 373, PBW 154, PBW 343, PBW 138, and Triticum durum L. cvs. PBW 34 and PDW 233) grown in a screen house in India. The soil was a loamy sand with pH 8.1, DTPA‐extractable Mn 1.62 mg (kg soil)^–1, and initial soil solution Mn concentration (C_Li) of 0.19 μM. When fertilized with 50 mg Mn (kg soil)^–1, C_Li increased to 0.32 μM. At C_Li 0.19 μM, wheat cv. PBW 373 produced 74% of its maximum shoot dry weight (SDW) with 64% of its maximum root length (RL), while cv. PDW 233 produced only 25% of its maximum SDW with 11% of its maximum RL. The other wheat cultivars were between these extremes. Manganese deficiency caused a reduction in shoot growth, but more strongly reduced root growth. The low Mn efficiency of T. durum cv. PDW 233 was related to a strong depression of its root growth. Manganese influx was similar for all cultivars. In solution culture below 1 μM Mn, under controlled climate‐chamber conditions, Mn influx was linearly related to Mn concentration. Both the efficient cv. PBW 343 and the inefficient cv. PDW 233 had a similar influx. Uptake kinetic parameters from the solution experiment together with soil and plant parameters from the pot experiment were used in a mechanistic nutrient‐uptake model. Calculated values of Mn influx for wheat grown in soil were 55% to 74% of measured values. A sensitivity analysis showed that increasing C_Li or the slope of the uptake isotherm by about 30% would be enough to reach the observed influx. The results of this research indicate that an increase of Mn solubility by microbial or chemical mobilization would increase Mn uptake. But on the other hand, no chemical mobilization would be required to increase Mn uptake if the plant improved its uptake kinetics. Low Mn efficiency of some wheat cultivars was related to their reduced root growth at low soil Mn supply.     

Differences in manganese efficiency of wheat (Triticum aestivum L.) and raya (Brassica juncea L.) as related to root‐shoot relations and manganese influx

Manganese efficiency is a term used to describe the ability of plants to obtain higher relative yields at low Mn supply compared to other species. To evaluate Mn efficiency of wheat (Triticum aestivum L.) and raya (Brassica juncea L.), a greenhouse pot experiment was conducted using Mn deficient Typic Ustochrept loamy sand soil, treated with 0, 50, and 100 mg Mn (kg soil)^–1. In the no‐Mn treatment, wheat had produced only 30 % of its maximum dry matter yield (DMY) with a shoot concentration of 10.8 mg Mn (kg DM)^–1 after 51 days of growth, while raya had produced 65 % of its maximum DMY with 13.0 mg Mn (kg DM)^–1. Taking relative shoot yield as a measure of Mn efficiency, raya was more efficient than wheat. Both crops produced the maximum DMY with 50 mg Mn (kg soil)^–1. Even though raya had a lower root length : DMY ratio and a higher shoot growth rate, it acquired higher Mn concentrations in the shoot than wheat under similar soil conditions, because of a 2.5 times higher Mn influx. Model calculations were used to calculate the difference of Mn solution concentration (ΔC_L) between the bulk soil (C_Li) and the root surface (C_L0) that is needed to drive the flux by diffusion equal to the measured influx. The results showed that ΔC_L was smaller than C_Li, which indicates that chemical mobilization of Mn was not needed to explain the observed Mn uptake even for raya. According to these calculations, the higher Mn influx of raya was caused by more efficient uptake kinetics, allowing for a 4.5 times higher Mn influx at the same Mn concentration at the root surface.     

Phosphorus Influx and Root‐Shoot Relations as Indicators of Phosphorus Efficiency of Different Crops

Abstract

The large variation in phosphorus acquisition efficiency of different crops provides opportunities for screening crop species that perform well on low phosphorus (P) soil. To explain the differences in P efficiency of winter maize (Zea mays L.), wheat (Triticum aestivum L.), and chickpea (Cicer arietinum L.), a green house pot experiment was conducted by using P‐deficient Typic ustochrept loamy sand soil (0.5 M NaHCO₃‐extractable P 4.9 mg kg^?1, pH 7.5, and organic carbon 2.7 g kg^?1) treated with 0, 30, and 60 mg P kg^?1 soil. Under P deficiency conditions, winter maize produced 76% of its maximum shoot dry weight (SDW) with 0.2% P in shoot, whereas chickpea and wheat produced about 30% of their maximum SDW with more than 0.25% P in shoot. Root length (RL) of winter maize, wheat, and chickpea were 83, 48, and 19% of their maximum RL, respectively. Considering relative shoot yield as a measure of efficiency, winter maize was more P efficient than wheat and chickpea. Winter maize had lower RL/SDW ratio than that of wheat, but it was more P efficient because it could maintain 2.2 times higher P influx even under P deficiency conditions. In addition, winter maize had low internal P requirement and 3.3 times higher shoot demand (i.e., higher amount of shoot produced per cm of root per second). Even though chickpea had 1.2 times higher P influx than winter maize, it was less P efficient because of few roots (i.e., less RL per unit SDW). Nutrient uptake model (NST 3.0) calculations satisfactorily predicted P influxes by all the three crops under sufficient P supply conditions (C_Li 48 µM), and the calculated values of P influx were 81–99% of the measured values. However, in no‐P treatment (C_Li 3.9 µM), under prediction of measured P influx indicated the importance of root exudates and/or mycorrhizae that increase P solubility in the rhizosphere. Sensitivity analysis showed that in low P soils, the initial soil solution P concentration (C_Li) was the most sensitive factor controlling P influx in all the three crops.     

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.     

NITROGEN SOURCE AND MANGANESE APPLICATION EFFECTS ON MANGANESE DYNAMICS IN THE RHIZOSPHERE OF WHEAT CULTIVARS GROWN ON MANGANESE-DEFICIENT SOILS

To study the effect of two different nitrogen (N) sources and manganese application on root-shoot relations and manganese (Mn) dynamics in the rhizosphere of two wheat cultivars, a screen house experiment was conducted using manganese-deficient soil. Significantly higher root length (RL), root surface area, shoot dry weight (SDW), root length density, and manganese uptake were recorded in calcium nitrate supplied plants of cultivar ‘WH 542’ when applied with calcium nitrate along with manganese rather than ammonium sulfate. Cultivar ‘PD W274’ produced 72% of the maximum RL and 77% of the maximum SDW under similar conditions. Results indicated that cultivar ‘WH 542’ was more manganese efficient than ‘PD W274’ and calcium nitrate was a better source of nitrogen than ammonium sulfate. However, maximum shoot manganese content was recorded in ammonium sulfate supplied plants, which was due to depletion of manganese at root surface to a lower value, causing higher concentration gradient and hence higher manganese influx to root.     

MANGANESE EFFICIENCY OF WHEAT CULTIVARS AS RELATED TO ROOT GROWTH AND INTERNAL MANGANESE REQUIREMENT

ABSTRACT

Under field conditions, wheat cultivar PBW 343 produced 1.5 times higher grain yield than PDW 233, when grown on low manganese (Mn) soil. To explain the differences in Mn efficiency a pot experiment was conducted using Mn deficient Typic ustochrept loamy sand soil treated with 0, 50, and 100?mg?Mn?kg^?1 soil. In no-Mn treatment, both the wheat cultivars showed Mn deficiency symptoms and cultivar PBW 343 produced 30% of the maximum dry matter yield (DMY) attained at high Mn supply, while PDW 233 produced only 18% of its maximum DMY after 40 days of growth. With application of 50?mg?Mn?kg^?1 soil, the DMY significantly increased to 87% and 50% of the maximum for PBW 343 and PDW 233, respectively. These results indicate that aestivum cultivar PBW 343 was more Mn efficient than durum cultivar PDW 233. Manganese efficient cultivar PBW 343 had a lower internal Mn requirement than PDW 233 because at the same shoot Mn concentration PBW 343 produced more DMY. The root growth of both wheat cultivars was similar at sufficient Mn supply, the root length (RL)?:?DMY ratio being equal. At decreasing Mn supply root growth was depressed more strongly than shoot growth, the inhibition being more severe in Mn inefficient cultivar PDW 233, indicating the importance of root system size for Mn efficiency between these two wheat cultivars. A nutrient uptake model closely described Mn influx in both the cultivars, indicating that calculated concentration profiles were realistic and that chemical mobilization of Mn in the rhizosphere was not responsible for higher Mn efficiency of PBW 343. Calculated concentration profiles showed that in soil not fertilized with Mn, initial soil solution Mn concentration of 0.23?µM decreased to only 0.21?µM at the root surface after 27 days of uptake. This 7.4% decrease in Mn concentration at the root surface indicated that roots could not decrease Mn concentration to a lower value which would have caused higher transport of Mn to root surface and hence resulted in higher Mn influx.     

Comparative Phytoremediation of Chromium‐Contaminated Soils by Fenugreek,Spinach, and Raya

Abstract

A glasshouse investigation was undertaken to evaluate the natural potential of fenugreek (Trigonella foenumgraecum L.), spinach (Spinacia oleracea L.), and raya (Brassica campestris L.) for cleanup of chromium (Cr)–contaminated silty loam and sandy soils. Four kilograms of soil per treatment in earthen pots was treated with five levels of chromium [0, 1.25, 2.5, 5.0, and 10.0 mg Cr kg^?1 soil through dipotassium chromate (K₂Cr₂O₇], equilibrated for 21 days at field-capacity moisture content, and then fenugreek, spinach, and raya were grown for 60 days after seeding. The concentration of diethylene triamine pentaacetic acid (DTPA)‐extractable Cr increased significantly with increasing rate of Cr application in both soils, but the increase was higher in sandy soil than in silty loam soil. The DTPA‐extractable Cr in both soils decreased after harvesting of crops compared to its concentration in soil before sowing of the crops. The decrease in DTPA‐extractable Cr concentration was highest in soil growing raya and least in the fenugreek‐growing soil. The percent reduction in dry‐matter yield (DMY) with increasing levels of added Cr in comparison to the zero‐Cr control was highest for fenugreek (49 and 52%) followed by spinach (36 and 42%) and lowest for raya (29 and 34%) in silty loam soil and sandy soil, respectively. Also, the percent reduction in mean shoot yield of all crops was higher in sandy soil (41%) compared to silty loam soil (36%), when the rate of applied Cr was increased from 0 to 10 mg Cr kg^?1 soil. The DMY of both shoot and root was highest for raya and lowest for fenugreek. The Cr concentration in fenugreek, spinach, and raya increased with increasing level of added Cr in both soils. The concentration of Cr in both shoot and root was highest in raya, followed by spinach and fenugreek. The overall mean uptake of Cr in shoot was almost four times and in root was about two times higher in raya compared to fenugreek. The findings indicated that family Cruciferae (raya) was most tolerant to Cr toxicity, followed by chenopodiacea (spinach) and Leguminosae (fenugreek). Because raya removed the highest amount of Cr from soil, it could be used for pytoremediation of mildly Cr‐contaminated soils.     

Manganese deficiency in wheat genotypes: Physiological responses and manganese deficiency tolerance index

Manganese (Mn) deficiency limits wheat productivity on sandy loam, calcareous and alkaline soils cropped with rice. Variation of wheat genotypes to sustain production and Mn use from Mn deficient condition was investigated to screen efficient genotypes. Forty-seven diverse wheat genotypes were evaluated on Mn sufficient (0.195 µM) and Mn deficient (0 µM) nutrient solution to elucidate physiological basis of Mn deficiency tolerance and to develop manganese deficiency tolerance index (MDTI). Shoot dry weight and mean Mn accumulation was 136.7% and 76.5% enhanced when Mn nutrition was improved, respectively. Efficient genotypes under limited Mn had lower root length/shoot weight ratio but higher relative shoot growth rate with higher shoot demand on root which reflected higher Mn influx. Genotypes were classified as tolerant (>0.66), semi-tolerant (0.33–0.66) and sensitive (<0.33) on the basis of MDTI (0–1 scale). Manganese efficient genotypes are most desirable for sustainable production of wheat under low Mn.     

Water stress and mycorrhizal isolate effects on growth and nutrient acquisition of wheat

Arbuscular mycorrhizal (AM) colonized plants often have greater tolerance to drought than nonmycorrhizal (nonAM) plants. Wheat (Triticum durum Desf.), whose roots were colonized with Glomus mosseae (Gms) and G. monosporum (Gmn), were grown in a greenhouse to determine effects of water stress (WS) on shoot and root dry matter (DM), root length (RL), and shoot phosphorus (P), zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe) concentrations and contents. Mycorrhizal colonization was higher in well‐watered (nonWS) plants colonized with both AM isolates than WS plants, and Gms had greater colonization than Gmn under both soil moisture conditions. Shoot and root DM were higher in AM than in nonAM plants irrespective of soil moisture, and Gms plants had higher shoot but not root DM than Gmn plants grown under either soil moisture condition. Total RL of AM plants was greater than nonAM plants, but was consistently lower for plants grown with WS than with nonWS. The AM plants had similar shoot P and Mn concentrations as nonAM plants, but contents were higher in AM than in nonAM plants. The AM plants had higher shoot Zn, Cu, and Fe concentrations and contents than nonAM plants. The Gms plants grown under nonWS generally had higher nutrient contents than Gmn plants, but nutrient contents were similar for both Gms and Gmn plants grown under WS. The results demonstrated a positive relationship between enhanced growth and AM root colonization for plants grown under nonWS and WS.     

Role of Phosphatases,Iron Reducing,and Solubilizing Activity on the Nutrient Acquisition in Mixed Cropped Peanut and Barley

The effect of interspecific complementary and competitive root interactions and rhizosphere effects on primarily phosphorus (P) and iron (Fe) but also nitrogen (N), potassium (K), calcium (Ca), zinc (Zn), and manganese (Mn) nutrition between mixed cropped peanut (Arachis hypogaea L.) and barley (Hordeum vulgare L.). In order to provide more physiological evidence on the mechanisms of interspecific facilitation, phosphatase activities in plant and rhizosphere, root ferric reducing capacity (FR), Fe-solubilizing activity (Fe-SA), and rhizosphere pH were determined. The results of the experiment revealed that biomass yield of peanut and barley was decreased by associated plant species as compared to their monoculture. Rhizosphere chemistry was strongly and differentially modified by the roots of peanut and barley and their mixed culture. In the mixed cropping of peanut/barley, intracellular alkaline and acid phosphatases (AlPase and APase), root secreted acid phosphatases (S-APase), acid phosphatases activity in rhizosphere (RS-APase), and bulk soil (BS-APase) were higher than that of monocultured barley. Regardless of plant species and cropping system, the rhizosphere pH was acidified and concomitantly to this available P and Fe concentrations in the rhizosphere were also increased. The secretion Fe-solubilizing activity (Fe-SA) and ferric reducing (FR) capacity of the roots were generally higher in mixed culture relative to that in monoculture treatments which may improve Fe and Zn nutrition of peanut. Furthermore, mixed cropping improved N and K nutrition of peanut plants, while Ca nutrition was negatively affected by mixed cropping.     

Unraveling the Effect of Differentially Applied Manganese on Root Dynamics and Efficiency of Diverse Rice Genotypes

Increasing manganese (Mn) deficiency in soils emphasizes strategies for breeding genotypes with increased Mn efficiency. The present investigation evaluated Mn efficiency of 11 rice genotypes w.r.t. basal, foliar, and basal+foliar Mn application in field and glasshouse conditions. The genotypes with B + F application had higher leaf area (LA), SPAD index, root length (RL), root surface area (RSA) and mean half distance between roots (MHDR), and ultimately higher Mn efficiency under both growing conditions. The results of correlation analysis depicted strong positive relation between grain yield and LA (0.60) and SPAD index (0.53). The root characteristics viz., RL, RSA, and MHDR could, respectively, explain 76%, 77%, and 83% of variation in grain yield emphasizing the importance of superior root geometry in regulating mechanism pertaining to differential Mn efficiency. The breeders could select the traits for better root geometry along with high yield in breeding programs to develop Mn efficient genotypes.     

Potassium efficiency mechanisms of wheat,barley, and sugar beet grown on a K fixing soil under controlled conditions

Plant species differ in their potassium (K) efficiency, but the mechanisms are not clearly documented and understood. Therefore, K efficiency of spring wheat, spring barley, and sugar beet was studied under controlled conditions on a K fixing sandy clay loam. The effect of four K concentrations in soil solution ranging from low (5 and 20 μM K) to high (2.65 and 10 mM K) on plant growth and K uptake was investigated at 3 harvest dates (14, 21, and 31 days after sowing). The following parameters were determined: shoot dry matter (DM), K concentration in shoot dry matter, root length (RL), root length/shoot weight ratio (RSR), shoot growth rate/average root length ratio (GR_s/aRL), K influx, and soil solution K concentrations. Wheat proved to have a higher agronomic K efficiency than barley and sugar beet, indicated by a greater relative yield under K‐deficient conditions. As compared to both cereals, sugar beet was characterized by higher K concentrations in the shoot dry matter, only 30—50 % of the root length, 15—30 % of the RSR and a 3 to 6 times higher GR_s/aRL. This means that the shoot of sugar beet had a 3 to 6 times higher K demand per unit root length. Even at low K concentrations in the soil solution, sugar beet had a 7 to 10 times higher K influx than the cereals, indicating that sugar beet was more effective in removing low available soil K. Wheat and barley were characterized by slow shoot growth, low internal K requirement, i.e. high K utilization efficiency, and high RSR, resulting in a low K demand per unit root length. At low soil K concentrations, both cereals increased K influx with age, an indication of adaptation to K deficiency. The mechanism of this adaptation merits closer investigation. Model calculations were performed to estimate the K concentration difference between the bulk soil and the root surface (ΔC_L) needed to drive the measured K influx. For the two cereals, the calculated ΔC_L was smaller than the K concentration in the soil solution, but for sugar beet, ΔC_L was up to seven times higher. This indicates that sugar beet was able to mobilize K in the rhizosphere, but the mechanisms responsible for this mobilization remain to be studied.     

Manganese toxicity in tomato plants: Effects on cation uptake and distribution

Two experiments are described in which tomato plants (Lycopersicon esculentum L. var Ailsa Craig) were grown in water culture supplied with 10–300 μM Mn. Toxicity symptoms associated with a yield reduction were observed only in treatments in excess of 50 μM Mn indicating that this species is relatively tolerant of high Mn supply. Dark brown/black spots appeared first in the cotyledons. Similar symptoms were observed in the leaves, progressively from the oldest leaf. Manganese concentration in the shoot tissues ranged from 286 to 4240 μg. g^‐1 dry weight. The high Mn concentration values found in the shoot tissues of the toxic plants indicate that Mn was highly mobile in the xylem as confirmed by xylem sap analysis.

The concentrations of both Ca and Mg were lower in the smaller Mn toxic plants. Not only was uptake of Ca and Mg retarded but so also was the distribution of Ca and Mg to the younger tissues as illustrated by measurements of Ca and Mg concentrations along a leaf age sequence. This is in accord with the cation‐anion balance of the xylem exudates collected from decapitated plants.

Higher cation exchange capacity (CEC) was found in the leaf tissues of toxic plants particularly in the older leaves but similar values of C.E.C were recorded for the younger leaf tissues of both control and toxic plants.     

Phenotypic variations of wheat cultivars from the North China Plain in response to cadmium stress and associated single nucleotide polymorphisms identified by a genome-wide association study

Understanding the genetic mechanisms for cadmium(Cd) uptake and translocation in common wheat(Triticum aestivum) is of significance in food Cd contamination control. In this study, a diverse panel of 132 wheat cultivars was collected from the North China Plain. The cultivars were evaluated in terms of their phenotypic variations in response to Cd stress and subjected to a genome-wide association study(GWAS) to identify single nucleotide polymorphisms(SNPs) associated with the phenotypic variatio...     

Manganese Deficiency in Canola Induced by Liming to Ameliorate Soil Acidity

Applying lime to ameliorate soil acidity has been observed to induce manganese (Mn) deficiency in canola (Brassica napus L.) crops grown on acid sandy soils near Albany and gravelly acid sands of the Great Southern Districts of southwestern Australia. These soils were often Mn-deficient in patches for wheat (Triticum aestivum L.) production when they were newly cleared for agriculture requiring application of Mn fertilizer to ensure grain yields were not reduced by the deficiency. Since then, these soils have acidified and in the 1990s, canola started to be grown on these soils in rotation with wheat and lupins (Lupinus angustifolius L.). These limed soils may now have become marginal to deficient in Mn for canola production. The effect of liming may change the effectiveness of fertilizer Mn. In addition, the effect of liming on the residual value of Mn fertilizer applied to these soils for canola production is unknown. Therefore, a glasshouse experiment was conducted using Mn deficient sand. Three levels of finely-powdered calcium carbonate were added and incubated in moist soil for 42 days at 22±2°C to produce 3 soils with different pH values [1:5 soil:0.01 M calcium chloride (CaCl₂)]: 4.9 (original soil), 6.3, and 7.5. Five Mn levels, as solutions of Mn sulfate, were then added and incubated in moist soil for 0, 50, and 100 days before sowing canola. To estimate the residual value (RV) of incubated Mn for canola production, the effectiveness of the incubated Mn was calculated relative to the effectiveness of Mn applied just before sowing canola (freshly-applied Mn). The RV of the incubated Mn was determined using yield of dried canola shoots, the Mn application level required to produce 90% of the maximum shoot yield, and Mn content in dried shoots (Mn concentration in shoots multiplied by yield of dried shoots). As measured using both yield of dried shoots and Mn content of dried shoots, the residual value of Mn decreased with increasing soil pH and with increasing period of incubation of Mn with moist soil. The critical Mn concentration, for 90% of the total yield of dried canola shoots, was (mg Mn kg^?1) ～17 in youngest mature growth (apex and youngest emerged leaf, YMG), and ～22 for the rest of dried shoots. These values were similar to current critical values for un-limed soils suggesting critical Mn concentrations remain the same for limed soils. Plant testing of canola is recommended if soils are to be limed to ameliorate soil acidity. When plant tests indicate a high likelihood of Mn deficiency, foliar Mn sprays need to be applied to that crop to ensure Mn deficiency does not reduce grain production that year, and fertilizer Mn needs to be re-applied to the soil when sowing the next crop to reduce the likelihood of Mn deficiency for subsequent crops.     

Aluminum effects on micronutrient uptake by annual ryegrass

Abstract

Four ryegrass (Lolium multiflorumLam.) cultivars were grown in 1/5 Steinberg nutrient solution supplemented with six Al levels (0, 37, 74, 148, 296, or 592 umol L^‐1) at pH initially adjusted to 4.2. Average net Fe influx was stimulated at low nutrient solution Al levels. This stimulation was larger for more Al‐tolerant cultivars Marshall and Gulf. Decreases in average net Mn and Zn influxes were brought about by increasing Al levels in the nutrient solution. The average net influx of Fe, Mn, and Zn was positively correlated with the root tolerance index (relative root yield of plants grown with and without Al added to the nutrient solution). For more Al‐tolerant cultivars, increased total uptake of Fe and Cu was brought about by increased nutrient solution Al levels up to 74 umol L^‐1. Decreases in total uptake of Mn and Zn were generally noted with increased nutrient solution Al levels. Percentage inhibition of total Fe, Mn, Zn, and Cu uptake was negatively correlated with the mean pH of the Al‐containing nutrient solutions. The higher average net influx and the smaller percentage inhibition of total Fe uptake at nutrient solution Al levels up to 74 umol L^‐1can be used as indicators in ranking ryegrass cultivars as more Al‐tolerant     

Chemical and physical fractions of manganese in soil during intensive ryegrass cropping

Abstract

Ryegrass was grown under greenhouse conditions in pots containing two types of calcareous soil. After 8 harvests, the soil was left in the pots for a simulated fallow period, then reseeded with ryegrass, from which 4 further harvests were obtained. The manganese (Mn) content in the soil samples, taken before seeding and after intensive cropping, was fractionated chemically and physically. Although different trends were apparent in the different fractions, ryegrass cropping enhanced the overall mobilization of soil Mn, which easily surpassed the cumulative Mn uptake. The organically bound Mn and clay‐associated Mn fractions released significant amounts of the element, whereas the behavior of exchangeable Mn, Fe‐oxide associated Mn and sand‐associated Mn fractions varied in the two different soils studied. The silt‐associated Mn fractions increased significantly in both soils.     

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.     

Response of Different Crops to Arbuscular Mycorrhiza Fungal Inoculation in Phosphorus-Deficient Soil

Arbuscular mycorrhizal fungi (AMF) have the capability to improve crop yields by increasing plant nutrient supply. A pot experiment was conducted under natural conditions to determine the response of AMF inoculation on the growth of maize (Zea mays L.), sorghum (Sorghum bicolor L.), millet (Pennisetum glaucum L.), mash bean (Vigna mungo L.), and mung bean (Vigna radiata. L.) crops during 2008. The experiment was conducted as a completely randomized design in three replications using phosphorus (P)–deficient soil. Three plants were grown in 10 kg soil up to the stage of maximum growth for 70 days. Spores of AMF were isolated from rhizosphere of freshly growing wheat and berseem crops and mixed with sterilized soil with fine particles. Crops were inoculated in the presence of indigenous mycorrhiza with the inoculum containing 20 g sterilized soil mixed with 40–50 AMF spores. Inoculation with AMF improved yield and nutrient uptake by different crops significantly over uninoculated crops. Inoculated millet crop showed 20% increase in shoot dry matter and 21% in root dry matter when compared with other inoculated crops. Increases of 67% in plant nitrogen (N) and iron (Fe) were observed in millet, 166% in plant P uptake was observed in mash beans, 186% in zinc (Zn) was measured in maize, and 208% in copper (Cu) and 48% in manganese (Mn) were noted in sorghum crops. Maximum root infection intensity of 35% by AMF and their soil spore density were observed in millet crop followed by 32% in mash beans. Results suggest that inoculation of AMF may play a role in improving crop production and the varied response of different crops to fungi signifies the importance of evaluating the compatibility of the fungi and plant host species.     

Comparison for plant uptake of phenanthrene and pyrene from soil and water

In this study, we evaluated (1) the plant uptake of polycyclic aromatic hydrocarbons (PAHs) from soil and water and (2) the applicability of the partition-limited model on the prediction of plant concentrations with respect to PAH contents in soils and other associated parameters. To accomplish these goals, the plant uptake of PAHs from culture solution and soils were extensively experimented. A steady state was shown for ryegrass kinetic uptake of phenanthrene and pyrene from water after about 48 h. As to the ryegrass uptake from soils, root and shoot concentrations of PAHs generally increased, while root concentration factors (RCFs) and shoot concentration factors (SCFs) tended to decrease with the increasing PAH concentrations in soils after 45 days. One note of interest is that root concentrations and RCFs of phenanthrene and pyrene for ryegrass uptake were larger than shoot concentrations and SCFs, irrespective of soil–plant and water–plant systems. However, root and shoot concentrations, or RCFs and SCFs, for ryegrass uptake from culture solution were always much higher than those for ryegrass uptake from soils at the same PAH concentrations in water or soil interstitial water, indicating that PAHs in culture solution would be more available and susceptible than those in soil interstitial water for uptake by plants. In addition, the partition-limited model showed a high level of model performance on prediction of plant uptake of phenanthrene and pyrene from soils, with the overall differences of the modeled and experimented concentrations in ryegrass roots or shoots less than 187%. This suggests that the partition-limited model might be a potentially useful instrument for vegetation-contamination assessment.