Effects of aluminium on growth and cation uptake in seedlings of Eucalyptus mannifera and Pinus radiata

This experiment was designed to examine the effects of aluminium (Al) on the growth of Pinus radiata (D. Don) and Eucalyptus mannifera subsp. mannifera (Mudie) seedlings in culture solutions in a glasshouse to help explain the failure of radiata pine trees on some acid, low fertility soils in Australia on which the native eucalypts flourish. Aluminium (Al) in culture solution increased the growth of roots and shoots of seedlings of both species but while growth of the eucalypt continued to increase with increases in Al to 2.222 μM, growth of the pine was largest at 370 μM Al. In addition to total root length, specific root length (length per unit dry weight), a measure of fineness of the root, increased in the eucalypt seedlings as the substrate Al increased. Growth of the shoots and roots of the pine in the absence of any added Al was extremely poor suggesting that Al, in low concentrations, may be an essential element or ameliorate some other factors in solution culture at low pH. Root and shoot concentrations of K increased with increasing Al, whilst Ca and Mg Concentrations decreased and Mn concentrations were unaffected in both species. Tissue Ca and Mg concentrations were 2 to 3 times higher in the eucalypt seedlings than the pine at all levels of added Al due to greater uptake of these elements by the eucalypt. In contrast, at the highest concentration of Al in the medium, shoot Al concentrations were lower in the cucalypt than in the pine due to a greater proportion of Al being retained in the eucalypt roots. These differences between the seedlings in terms of root growth and tissue cation concentrations may help explain the ability of eucalypt species to maintain vigorous growth on acid soils high in Al and low in Ca and P, where growth of the pines failed.     

Iron Enhances Aluminum-induced Leaf Necrosis and Plant Growth Inhibition in Eucalyptus camaldulensis

The combined effects of excess Fe and Al on Eucalyptus camaldulensis Dehnh. were studied by investigating time course and visible symptoms of leaf necrosis, plant biomass, the status of some antioxidants and pigments and nutrient concentrations. Seedlings were grown hydroponically in nutrient solutions containing 0 or 500 μM AlCl₃, each with a FeSO₄ range of 1, 12 and 120 μM at pH 4.2. Leaf necrosis and plant growth inhibition were induced by Al and enhanced by the increase in Fe concentration. The process from the first appearance of necrotic spots to leaf death (shedding) of a leaf proceeded from a few days to about 20 days after the leaf had fully expanded. Either 120 μM Fe without Al or Al reduced plant growth to a similar extent but 120 μM Fe without Al did not cause leaf necrosis. In leaves, excess Fe (12 and 120 μM) without Al reduced concentration of ASC and GSH, while concentration of Fe, DHA and GSSG and DHA:ASC and GSSG:GSH ratios tended to increase with the increase in Fe concentration in treatment solution with or without Al. At 1 μM Fe, Al increased concentration of DHA and DHA:ASC and GSSG:GSH ratios. Catalase activity in leaves reduced with the increase in leaf Al concentration. At 1 μM Fe, Al greatly reduced concentrations of Fe and chlorophylls in leaves but increase two times Fe concentration in stems. These suggest that the enhancement effects of Fe on Al-induced leaf necrosis and plant growth inhibition can be discussed in context of the excess Fe itself weakens antioxidant capability of ASC–GSH cycle in leaves and greatly reduces plant growth; and the increase in Fe accumulation in stems is involved in Al-induced leaf chlorosis.     

The influence of some soil and plant factors on the concentration of copper in perennial ryegrass

Summary The absorption and transport of Cu were studied in perennial ryegrass grwon on 21 soils under controlled environment conditions. Neither the concentration, nor the total amount, of Cu in the shoots was related to available Cu in the soils as assessed by extraction with 0.05M EDTA, 0.005M DTPA, or 1.95 per cent HNO₃. The concentration in the roots and, more especially, absorption per unit weight of root (i.e. μg Cu g dry wt⁻¹) were, however, highly correlated with available soil Cu. This suggests that, unless the extent of exploitation of the soil by roots is taken into account, measurements of available Cu will not be effective in predicting uptake by plants. On average, 63 per cent of the Cu absorbed by the roots was retained in the roots, and variation in the proportion retained was related to the transport of nitrogen from roots to shoots. On some soils the concentrations of N and Cu in the shoots were significantly correlated, and variation in N concentration accounted for a considerable proportion of the variance in the Cu concentration at later harvests. The relative importance of the measured soil (pH, organic matter) and plant (dry weight, N content) factors changed markedly over 6 successive harvests.     

The effect of aluminium on growth of and nitrogen fixation in vegetable soybean germplasm

Vegetable soybeam germplasm was screened for its tolerance to 0, 50 and 100 μM Al in solution culture. Plants were inoculated with prescreened acid-Al tolerantBradyrhizobium japonicum strain USDA 110 and a localRhizobium isolate SM867. Aluminum concentrations of 0, 50, and 100 μM affected the root lengths of all germplasm lines in the first few weeks of their growth. At 100 μM, the plants had severely stunted roots throughout the growing period of 35 days, but at 50 μM the initial stunting of the roots was overcome after the third week of growth, and there were no significant differences between the root lengths of these plants and of the controls. The appearance of the first nodule was delayed for 2–3 and 4–5 days at 50 μM and 100 μM Al, respectively. There was a significant reduction in nodule numbers and acetylene reduction activity (ARA) at 100 μM Al. At 50 μM Al, even though the number of nodules was decreased significantly, nodules were larger in size, so there was no significant reduction in nodule fresh weight and ARA. No significant differences in nitrogen fixing abilities of the soybean lines were observed between the twoRhizobium strains. Germplasm line Kahala showed the greatest tolerance to 50 μM Al, and Kahala, Kim and Wolverine tolerated 100 μM Al better than other germplasm lines.     

Manganese and iron interactions on their uptake and distribution in soybean (Glycine max (L.) Merr.)

Summary The uptake and distribution of iron and manganese were studied in a manganese-sensitive soybean cultivar (‘Bragg’) grown over a range of supply levels of these nutrients in solution culture. At high (90 and 275 μM) manganese levels, increasing the iron concentration in solution from 2 to 100 μM partially overcame the effects of manganese toxicity. Interactions between manganese and iron occurred for dry matter yields, rate of Mn absorption by the roots, and the proportions of manganese and iron transported to the tops. No interaction was observed for the rate of root absorption of iron. The percentage distribution of manganese in the plant top increased with increasing iron, despite a reduced rate of Mn uptake. On the other hand, iron uptake was independent of solution Mn concentration and increased with increasing solution Fe. Also more iron was retained in the roots at high Mn and/or Fe levels in solution. Concentrations of manganese and iron in roots, stems and individual leaves were affected independently by the manganese and iron supplyi.e. without any interaction occurring between the two elements. In general, the concentration in a plant part was related directly to the solution concentration. Symptoms resembling iron deficiency correlated poorly with leaf Fe concentrations whereas high levels of manganese were found in leaves displaying Mn toxicity symptoms.     

Chemistry of Cr in some Swedish soils

The effect of Si(OH)₄ on Cr toxicity and elemental concentrations in ryegrass were investigated in a growth chamber using an acid and a neutral mineral soil. Each soil was treated with 50 mg Cr, as CrO₃, kg⁻¹ soil dry weight, singly, or in combination with 25 mg Si as Si(OH)₄. Plants growing in unamended soils were used as controls. Chromium toxicity, expressed as decrease in shoot or root dry weight, was increased by the Si. This increase was accompanied by a higher Cr uptake particularly on the acid soil. The shoot and root dry weights were significantly correlated (P=1%) with the concentration of Cr, where r=−0.80 and −0.65, respectively. Uptake of Al, Cu, Fe, P and Zn did not show any consistent relationship to the magnitude of Cr toxicity.     

Trophic Transfer and Dietary Mineral Intake of Essential Elements in <Emphasis Type="Italic">Thunnus albacares</Emphasis> and <Emphasis Type="Italic">Katsuwonus pelamis</Emphasis> from the Eastern Pacific

With the aim of knowing levels of Cu, Fe, and Zn in the edible portion of tunas Thunnus albacares and Katsuwonus pelamis, these elements were measured in 73 fish collected in the eastern Pacific. Additionally, trophic transfer (TF) and dietary mineral intake (DMI) of analyzed metals were determined. The most elevated average concentration of Zn (31.7 μg g⁻¹ dry weight) was found in T. albacares from the Baja California region; in the case of Cu and Fe, highest values (3.86 and 71.0 μg g⁻¹ dry weight) were found in K. pelamis from the offshore waters in the Pacific Ocean. Concentrations of Cu in muscle tissue of both species were significantly (p < 0.05) correlated (negatively) with total length of specimens; levels of Fe in muscle of K. pelamis also showed a negative correlation with total length. None of TFs were above the unit, it implies that there is no biomagnification of Cu, Fe, and Zn. The DMI of Cu, Fe, and Zn from muscle tissue of analyzed tuna represented less than 13%, 21%, and 8%, respectively, of the daily requirements for humans.     

Aluminium tolerance in triticale,wheat and rye as measured by root growth characteristics and aluminium concentration

Summary Screening large populations of plant species for Al tolerance requires simple and rapid tests. In this study, root characteristics of 12 cultivars of triticale (X Triticosecale, Witt Mack), wheat (Triticum aestivum L.), and rye (Secale cereale L.) were measured in nutrient solution with 0 or 6 ppm Al added. Aluminum injury to roots of triticale and wheat was characterized by decreases in root length, increases in the number of roots, and in Al-sensitive Redcoat and Arthur wheats by decrease in root weight. Root length and number of roots were correlated in triticale (r=−0.73^*) and in wheat (r=−0.85^*). Root length was also correlated with root weight in wheat (r=0.65^*); there was no relationship between the number of roots and weight. Differences in Al tolerance of cultivars of the three species were greater when the solution was adjusted to pH 4.8 only on the first day of the experiment than when pH was maintained at pH 4.8 throughout the growing period. Triticale and rye cultivars low in ability to increase solution pH gradually overcame Al toxicity by increasing the nutrient solution pH between 12 and 22 days. Aluminum sensitive triticale and wheat accumulated more Al in roots than tolerant cultivars when the solution pH was not adjusted daily; but no differences in Al accumulation were obtained between wheat cultivars at constant pH value. This study indicated that root length and number of roots can be reliably used for screening triticales for Al tolerance within 12 days of exposure to Al. Root length, Al concentration, and dry weight after 22 days of Al treatment were also reliable criteria for evaluating differential Al tolerances among triticale cultivars.     

Aluminium toxicity and nodulation ofTrifolium repens

Summary Effects of aluminium on theTrifolium repens var Huia-Rhizobium trifolii strain HP3 symbiosis were studied using an axenic solution-culture system. With, 10 μM phosphate, 50 μM aluminium reduced or inhibited root elongation at pH<5.0, root hair formation at pH< 5.0–5.5, and Rhizobium multiplication in the rhizosphere and nodule formation at pH<6.0. In the absence of aluminium, root elongation and root hair formation were reduced at pH<4.3, and Rhizobium multiplication and nodule formation were inhibited at pH<5.0. Root hair formation was more sensitive to aluminium at pH<5 than was root elongation. No effect of aluminium on Rhizobium multiplication and nodule formation at pH<5 was detected because both were sensitive to pH alone. At pH 5.5 most of the aluminium changed immediately to a form which was susceptible to low-speed centrifugation, but which was detected by the aluminon method of analysis, and after 24 h a precipitate formed. the concentration of phosphate was reduced also, to approximately 1μM. Toxicity was overcome by either increasing the phosphate concentration from 10 to 50 μM, or by increasing the pH to 6.0 and the calcium, concentration to 1000μM.     

Soil acidity factors and nodulation ofTrifolium repens

Summary Effects of factors associated with soil acidity (low pH, low calcium, high aluminium and high manganese) on theTrifolium repens-Rhizobium trifolii symbiosis were investigted under laboratory conditions using an axenic solution-culture technique. 200 μM manganese increased root elongation in the range pH 4.3–5.5, but had no effect on root hair formation, the number of Rhizobium in the rhizosphere, or nodule formation. Root elongation and root hair formation were unaffected at pH 4.3 when 500 or 1000μM calcium was supplied, whereas multiplication of Rhizobium in the rhizosphere and nodulation were inhibited at pH 4.3 and 4.7.50–1000μM calcium had no effect either on the multiplication of Rhizobium in the range pH 4.3–5.5, or on nodule formation in the absence of aluminium. 50 μM aluminium inhibited, root elongation and root hair formation at pH 4.3 and 4.7; the effect on root elongation was reduced by increasing the calcium concentration from 50 to 1000μM. 50μM aluminium also inhibited Rhizobium multiplication in the rhizosphere and reduced nodule formation at pH 5.5 (at which aluminium precipitated out of solution), but root elongation and root hair formation were unaffected. These, effects of aluminium at pH 5.5 may explain the poor response to inoculation by white clover in acid mineral soils after liming.     

Characterization of natural variation for zinc, iron and manganese accumulation and zinc exposure response in Brassica rapa L.

Brassica rapa L. is an important vegetable crop in eastern Asia. The objective of this study was to investigate the genetic variation in leaf Zn, Fe and Mn accumulation, Zn toxicity tolerance and Zn efficiency in B. rapa. In total 188 accessions were screened for their Zn-related characteristics in hydroponic culture. In experiment 1, mineral assays on 111 accessions grown under sufficient Zn supply (2 μM ZnSO₄) revealed a variation range of 23.2–155.9 μg g⁻¹ dry weight (d. wt.) for Zn, 60.3–350.1 μg g⁻¹ d. wt. for Fe and 20.9–53.3 μg g⁻¹ d. wt. for the Mn concentration in shoot. The investigation of tolerance to excessive Zn (800 μM ZnSO₄) on 158 accessions, by using visual toxicity symptom parameters (TSPs), identified different levels of tolerance in B. rapa. In experiment 2, a selected sub-set of accessions from experiment 1 was characterized in more detail for their mineral accumulation and tolerance to excessive Zn supply (100 μM and 300 μM ZnSO₄). In this experiment Zn tolerance (ZT) determined by relative root or shoot dry biomass varied about 2-fold. The same six accessions were also examined for Zn efficiency, determined as relative growth under 0 μM ZnSO₄ compared to 2 μM ZnSO₄. Zn efficiency varied 1.8-fold based on shoot dry biomass and 2.6-fold variation based on root dry biomass. Zn accumulation was strongly correlated with Mn and Fe accumulation both under sufficient and deficient Zn supply. In conclusion, there is substantial variation for Zn accumulation, Zn toxicity tolerance and Zn efficiency in Brassica rapa L., which would allow selective breeding for these traits.     

Cadmium and copper interactions on the accumulation and distribution of Cd and Cu in birch (Betula pendula Roth) seedlings

The effect of different external cadmium (Cd) and copper (Cu) regimes on the concentration of Cd and Cu in roots and shoots of birch (Betula pendula Roth.) seedlings was investigated. The seedlings were grown for 12 days in a weak nutrient solution (containing all essential nutrient elements including 0.025 µM Cu) at pH 4.2 with combinations of additional 0–2 µM CdCl₂ and 0–2 µM CuCl₂. Root and shoot concentrations of Cu were decreased by Cd in all treatments which included 0.1–2 µM of additional Cu in the treatment solution. When no extra Cu was added, only the shoot concentration of Cu was decreased by Cd whereas the root concentration was not affected. The shoot concentration of Cd was decreased by 0.5 and 2 µM of additional Cu in the treatment solution. The root concentration of Cd was decreased by Cu only when the concentration of additional Cu in the treatment solution was equal to or exceeded the concentration of Cd.     

The effects of low concentrations of aluminium on the growth and uptake of nitrate-N by white clover

Summary The effects of aluminium (Al³⁺) at concentrations of 0, 25, 50 and 100 μM on the growth of white clover, dependent upon N supplied as NO ₃ ⁻ , were examined in flowing solution culture. Plants were established with a normal nutrient supply for 7 weeks and then grown with carefully controlled pH (at 4.5) and P concentrations, and with 0, 25, 50 or 100 μM Al³⁺ for a further three weeks. There were rapid visual effects (i.e. symptoms of P deficiency and reduction in root extension) and the dry weights of shoots and roots were reduced at 50 and 100 μM. Less than 10% of Al absorbed from solution was transported to the shoots. The uptake of P, and its transport between roots and shoots, were reduced in plants grown with Al. The uptake of NO ₃ ⁻ stopped immediately after the introduction of 50 or 100 μM Al, and was significantly reduced at 25 μM after three weeks. During a second phase of the experiment, plants previously grown at 0, 25, 50 and 100 μM Al, were grown for a further 2 weeks either with NO ₃ ⁻ (with and without 50 μM Al³⁺) or without NO ₃ ⁻ but with inoculation by Rhizobia (and with or without 50 μM Al³⁺). The effects of the previous treatments with Al on N uptake were small during the second phase, but uptake by all plants was restricted when Al was present. Inoculation did not result in nodulation in the second phase when Al³⁺ was present in the solution, but Al already in the plant from the first phase did not prevent nodulation in the absence of Al during the second phase.     

Aluminum accumulation and associated effects on 15NO3 − influx in roots of two soybean genotypes differing in Al tolerance

A study was conducted to examine aluminum (Al) exclusion by roots of two differentially tolerant soybean (Glycine max L. Merr.) lines, Pl-416937 (Al-tolerant) and Essex (Al-sensitive). Following exposure to 80μM Al for up to 2 h, roots were rinsed with a 10 mM potassium citrate solution and rapidly dissected to allow estimation of intracellular Al accumulation in morphologically distinct root regions. Using 10 min exposures to 300μM ¹⁵NO₃ ⁻ and dissection, accompanying effects on NO₃ ⁻ uptake were measured. With Al exposures of 20 min or 2 h, there was greater Al accumulation in all root regions of Essex than in those of Pl-416937. The genotypic difference in Al accumulation was particularly apparent at the root apex, both in the tip and in the adjacent root cap and mucilage. Exposure of roots to Al inhibited the uptake of ¹⁵NO₃ ⁻ to a similar extent in all root regions. The results are consistent with Al exclusion from cells in the root apical region being an important mechanism of Al tolerance.     

The effect of aluminium and media on the growth of mycorrhizal and nonmycorrhizal highbush blueberry plantlets

A factorial experiment was conducted to determine the effect of aluminium (0 and 600M) and media (sand, and 1:1 sand:soil) on mycorrhizal (M) and non-mycorrhizal (NM) highbush blueberry plantlets. There were no differences in nutrient uptake and total plant dry weight between M and NM plantlets. However, more root growth, as determined by dry weight, was observed in M than NM plantlets. The plantlets growing in sand had more dry weight than did those in the soil medium. Although the root growth and shoot growth were reduced by the 600M Al treatment, the direct effect of Al on plantlet growth was not clear due to Al and P interactions. Plant nutrient uptake was reduced by high concentrations of Al, suggesting that high Al concentration limited the ability of roots to acquire most of the nutrients. Mycorrhizal cortical cell infection levels of 15–20% wene maintained in the roots in soil medium but decreased to about 5% over the 6 weeks of the experiment in the sand medium. Although M plantlets accumulated more Al in their roots, Al was readily transported to the leaf tissues of M and NM plantlets.     

Aluminum inhibition of shoot lateral branches ofGlycine max and reversal by exogenous cytokinin

Aluminum effects on the morphological development of soybean (Glycine max (L.) Merr.) were characterized in greenhouse and growth chamber experiments. An Al-sensitive cultivar, ‘Ransom’, was grown in an acid soil (Aeric Paleudult) adjusted to 3 levels of exchangeable Al. Lateral shoot development at the nodes of the main stem was extensive in the limed soil containing 0.06 cmol(+) Alkg⁻¹. However, lateral shoot length and weight were severely inhibited in the unlimed soil containing 2.19 cmol(+) Alkg⁻¹, and in the unlimed soil amended to 2.63 cmol(+) Alkg⁻¹ with AlCl₃. This inhibition by the high Al/low pH condition was reversed by the exogenous application of a synthetic cytokinin 6-benzylaminopurine (BA). The daily application of 20 μg mL⁻¹ BA applied locally to the lateral meristems of plants grown in the unlimed soil stimulated lateral shoot growth substantially, such that it was either comparable to or greater than that observed in the limed treatment without BA. Accumulation of K, Ca, and Mg in lateral shoot branches was also stimulated by the local application of BA. The inhibitory effects of Al on lateral shoot development were confirmed in solution culture. In addition, differential sensitivity to Al was evident among the primary root, first order lateral roots, and second order lateral roots. The length of the primary root was only slightly decreased by increasing concentrations of Al up to 30 μM. In contrast, the length of basipetally located first order lateral roots was restricted to greater extent; up to 50% by 30 μM Al. Second order lateral lengths were inhibited even more severely; up to 86% by 30 μM Al. Substantial evidence in the literature indicates that the root apex is a major site for the biosynthesis of cytokinin that is supplied to shoots, and cellular function and development in this region of the root are impaired during Al toxic conditions. This suggests that one mode of action by which Al may affect shoot growth is by inhibiting the synthesis and subsequent translocation of cytokinin to the meristematic regions of the shoot. The present observation of a reversal of Al-inhibited lateral shoot development by exogenously applied cytokinin supports this hypothesis. However, the inability of applied cytokinin to counter the restriction imposed by Al on total shoot dry matter production implies the impairment by Al toxicity of other root functions, such as ion and water transport, also played an important role in altering shoot morphology.     

Adaptive Copper Tolerance in <Emphasis Type="Italic">Elsholtzia haichowensis</Emphasis> Involves Production of Cu-induced Thiol Peptides

Copper (Cu) accumulation and tolerance mechanisms in Elsholtzia haichowensis, an indicator plant of Cu mines, were investigated under hydroponics supplied with different concentrations (0.32, 50.0, 100.0 and 200.0 μM) of Cu for 8 days. Cu at 100 and 200 μM significantly decreased the root dry weight, but had no significant effect on shoot dry weight. The plants grown in the presence of 200 μM Cu accumulated 288 and 7626 μg g⁻¹ DW total Cu in the shoots and roots, respectively. A greater proportion of accumulated Cu was water-soluble accounting for 42–93% of the total Cu content in the shoots. The concentrations of reduced glutathione (GSH) and protein thiols were significantly enhanced under excess Cu supply. However, the concentrations of these compounds, particularly protein thiols, were much higher in the leaves than that in the roots. Three UV-absorbing peaks could be eluted out through gel filtration chromatography on Sephadex G-50. A large amount of Cu was detected in the UV-absorbing peaks in 40–50 and 70–90 ml elution fractions of the root extract, and in 40–50 and 120–140 ml elution fractions of the leaf extract. The results suggested that the adaptive Cu tolerance mechanism in E. haichowensis might involve the active participation of protein thiols which had a more important role in the leaves than in the roots.     

Manipulation of the morphogenetic pathways of Lilium longiflorum transverse thin cell layer explants by auxin and cytokinin

Summary Excised tissues from transverse young stem sections of Lilium longiflorum were cultured on Murashige and Skoog medium supplemented with growth regulators at various concentrations. After 45 d in culture, the presence of α-naphthaleneacetic acid (NAA) in the culture medium at 5.4 μM resulted in bulblet formation while 2,4-dichlorophenoxyacetic acid (2,4-D) at 2.2 μM resulted in root formation. The presence of IBA (indole-3-butyric acid) in the culture medium at 1.0 μM resulted in shoot formation while plantlet formation occurred when IBA was added at a concentration of 2.0 μM. When 1-phenyl-3-(1,2,3-thiadiazol-5-yl)-urea (TDZ) was added to the culture medium at 1.1 μM, protocorm-like bodies (PLBs) formed, while 2.2 μM resulted in shoot formation (on abaxial and adaxial surfaces). The presence of NAA and TDZ in the culture medium at 5.4 μM and 0.4, 1.1 or 2.2 μM, respectively, resulted in somatic embryo formation while NAA- and 6-benzylaminopurine-(BA) containing culture medium formed callus or bulblets. The establishment of different regeneration systems when explants are exposed to various growth regulators demonstrates that the choice of growth regulator combinations and concentrations are of significance in determining the morphogenetic response and plant regeneration capacity.     

Manganese dynamics in the rhizosphere and Mn uptake by different crops evaluated by a mechanistic model

Understanding of the mechanisms of Mn supply from the soil and uptake by the plants can be improved by using simulation models that are based on basic principles. For this, a pot culture experiment was conducted with a sandy clay loam soil to measure Mn uptake by summer wheat (Triticum aestivum L. cv. Planet), maize (Zea mays L. cv. Pirat) and sugar beet (Beta vulgaris L. cv. Orbis) and to simulate Mn dynamics in the rhizosphere by means of a mechanistic model. Seeds of three crops were sown in pots containing 2.9 kg soil in a controlled growth chamber. Root and shoot weight, Mn content of plants, root length and root radius were determined 8 (13 days in case of sugar beet) and 20 days after germination. Soil and plant parameters were determined to run nutrient uptake model calculations. Manganese content of the shoot varied from 25 mg kg^-1 for sugar beet to 34 mg kg^-1 for maize. Sugar beet had the lowest root length/shoot weight ratio but the highest relative shoot growth rate, resulting in the highest shoot demand on the root. This is reflected by the Mn influx which was 0.9 × 10^-7, 1.7 × 10^-7 and 2.5 × 10^-7 nmol cm^-1 s^-1 for wheat, maize and sugar beet, respectively. Nutrient uptake model calculations predicted similar influx values. Initial Mn concentration of 0.2 μM in the soil solution decreased to only 0.16 μM for wheat, 0.13 μM for maize and 0.11 μM for sugar beet at the root surface. This shows that manganese transport to the root was not a limiting step. This was confirmed by the fact that an assumed 20 times increase in maximum influx (I_max) increased the calculated Mn influx by 3.7 times. Sensitivity analysis demonstrated that for controlling Mn uptake the initial soil solution concentration (C _Li), the root radius (r₀), I_max and the Michaelis constant (K _m) were the most sensitive factors in the listed order. This revised version was published online in August 2006 with corrections to the Cover Date.     

Plant growth and nutrient uptake characteristics of Fe-deficiency chlorosis susceptible and resistant subclovers

The objective of this study was to evaluate the growth and nutrient-uptake characteristics of Fe-deficiency resistant and susceptible subclover (Trifolium subterraneum L., T. yanninicum Katzn. and Morley, T. brachcalycinum Katzn. and Morley) cultivars on a calcareous soil. Ten subclover cultivars showing varying susceptibilities to Fe-deficiency chlorosis (Karridale, Nangeela, Geraldton, Mt. Barker, Woogenellup, Larisa, Trikkala, Rosedale, Koala and Clare) were grown on a low-Fe, calcareous soil (Petrocalcic Paleustoll) under moist (18% water content, 85% of water holding capacity) and water-saturated conditions using a Cone-tainer^® culture system. Chlorosis and its correlation with growth traits and mineral nutrition of the 10 cultivars were examined. The Fe-deficiency susceptibilities of the 10 cultivars decreased in the above order under the moist condition, but in slightly different order under the saturated condition. Shoot and root dry weights, total dry weight, and root-to-shoot ratio were each negatively correlated with chlorosis under both soil-moisture conditions, as was total shoot content of P, Ca, Fe, Mn and Zn. Shoot P and Fe concentrations were each positively correlated with chlorosis under the moist soil condition. Iron and Cu utilization efficiencies (biomass per unit weight of nutrient) in the shoot were each negatively correlated with chlorosis under the moist soil condition. These results suggest that there may be several characteristics of Fe-deficiency chlorosis resistance in subclovers, such as a more effective soil-Fe mobilizing mechanism(s), more balanced nutrition, lower required Fe concentration in the shoot, higher shoot-Fe utilization efficiency, and higher root/shoot ratio under Fe-deficiency stress conditions.