Magnesium uptake by Al-stressed maize plants with special emphasis on cation interactions at root exchange sites

As aluminium (Al) severely inhibits magnesium (Mg) uptake by many plant species, Mg uptake and Mg-Al interactions in maize (Zea mays L.) were studied in a series of short and long-term experiments. A relationship between Mg uptake and the degree of Mg saturation of exchange or binding sites of the root apoplast (root-CEC) was studied by growing plants in solutions containing: (i) different concentrations of Al, calcium (Ca) and hydrogen (H) ions; and (ii) a number of organic complexes of Al. In short-term experiments, Ca had little effect on the Mg nutrition of maize plants. However, with increasing concentrations of Al and H ions in nutrient solution, there was a decrease in both the degree of Mg saturation of root-CEC and Mg uptake. Effects of pH on cation (H, Al, Mg, Ca) binding at the root apoplasm were pronounced and complicated because of a simultaneous change of H ion concentration, effective root-CEC and Al speciation. The behaviour of Al as organic Al complexes differed from that supplied as aluminium chloride (AlCl₃). In the presence of organo-Al complexes, less Mg was replaced from apoplastic binding sites and Mg uptake was inhibited less severely than with AlCl₃. In a long-term experiment, Al-citrate, in contrast with AlCl₃, was not phytotoxic to maize, expressed by the lack of any inhibition of shoot biomass production.     

Phosphate and calcium uptake in beech (Fagus sylvatica) in the presence of aluminium and natural fulvic acids

In the present study we examine the effects of Al on the uptake of Ca²⁺ and H₂PO^-₄ in beech (Fagus sylvatica L.) grown in inorganic nutrient solutions and nutrient solutions supplied with natural fulvic acids (FA). All the solutions used were chemically well characterized. The uptake of Al by roots of intact plants exposed to solutions containing 0, 0.15 or 0.3 mM AlCl₃ for 24 h, was significantly less if FA (300 mg l⁻¹) were also present in the solutions. The Ca²⁺(⁴⁵Ca²⁺) uptake was less affected by Al in solutions supplied with FA than in solutions without FA. There was a strong negative correlation between the Al and Ca²⁺ uptake (r²=0.98). When the Al and Ca²⁺ (⁴⁵Ca²⁺) uptake were plotted as a function of the Al³⁺ activity (or concentration of inorganic mononuclear Al), almost the same response curves were obtained for the -FA and +FA treatments. We conclude that FA-complexed Al was not available for root uptake and therefore could not affect the Ca²⁺ uptake. The competitive effect of Al on the Ca²⁺ uptake was also shown in a 5-week cultivation experiment, where the Ca concentration in shoots decreased at an AlCl₃ concentration of 0.3 mM. The effect of Al on H₂PO⁻₄ uptake was more complex. The P content in roots and shoots was not significantly affected, compared with the control, by cultivation for 5 weeks in a solution supplied with 0.3 mM AlCl₃, despite a reduction of the H₂PO⁻₄ concentration in the nutrient solution to about one-tenth. At this concentration Al obviously had a positive effect on H₂PO⁻₄ uptake. The presence of FA decreased ³²P-phosphate uptake by more than 60% during 24 h, and the addition of 0.15 or 0.3 mM AlCl₃ to these solutions did not alter the uptake of ³²P-phosphate.     

Elemental concentrations and correlations in winter micropopulations of Stephanodiscus rotula: an autecological study over a period of cell size reduction and restoration

The population of Stephanodiscus rotula in a temperate eutrophic lake was studied over a 2 month period (January to early March). Although during the study period nutrient concentrations in the lake water remained far in excess of phytoplankton requirements, no notable increase in chlorophyll levels was recorded. This suggests that algae were limited by shortage of light and low temperatures. Frequency distribution analysis of cell diameters showed a dramatic size reduction at the end of winter, followed by restoration of higher values by early spring. Electron probe X-ray microanalysis spectra from Stephanodiscus cells routinely showed peaks of Ca, K, Si, P, S, Fe, Al, Mn, Mg, Na and Cl, with substantial variation in elemental concentrations both between and within samples. End-of-winter reduction in the cell size coincided with a considerable depletion of intracellular chemical levels of Si, P, Cl and K and could be related to the concurrent decrease in dissolved organic C and increase in intracellular Al. Correlation and factor analysis of intracellular elemental concentrations showed that statistical elemental associations within Stephanodiscus cells were mainly determined by three factors, with P, Cl, Si and K showing higher loadings on the first, Ca, Mn and S on the second, and Fe, Ca and Al on the third factor. Significant correlations among the elements of the first association may indicate the importance of P (ATP), K (through involvement in P metabolism) and Cl (possibly charge balance) in the active Si uptake during the study period.     

Response of honelocust (Gleditsia triacanthos L.) to soil solution aluminium

Honeylocust (Gleditsia triacanthos L.) seedlings were grown for 72 days in soil from a BC horizon of a Spodosol altered by adding four levels of AlCl₃. Saturated paste extracts from controls to the highest AlCl₃ treatment contained, respectively, 85 to 831 M Al, 834 to 163 M Ca and 316 to 35 M Mg and had a pH of 4.4 to 4.0 Leaf, stem, and root concentrations of Al and P increased while those of Mg, Ca, and Zn decreased with increasing levels of Al. Growth decreased as Al, Al/Ca, and Al/Mg ratios in the extract increased. Growth was negatively related to tissue concentrations of Al, P, and Zn and positively related to tissue Mg and Ca. Growth was more closely correlated to elemental concentrations in the saturated paste extracts than in the SrCl₂ extracts (1 part 0.01M SrCl₂: 1 part moist soil).The research was supported by EPRI grant RD 2365-01 and by the University of Minesota College of Forestry and Minnesota Agricultural Experiment Station Project 074; listed as Minnesota Agricultural Experiment Station Scientific Series Paper.     

The Nutrition of the Freshwater Dinoflagellate Ceratium hirundinella*

A defined medium was devised for a freshwater isolate of the dinoflagellate Ceratium hirundinella. Highest cell yields were produced at 7,700–10,000 lux. The optimum pH range was between 7.0 and 7.5: the optimum temperature 21°C. Ceralium hirundinella tolerated a wide range (per liter) of Ca (0.1–100 mg) and Mg (0.1–50 mg) ion concentrations. The optimum range for growth was 20–30 rns Ca and 10–30 mg Mg. Cells cultured in media lacking Ca often became teratological yet motilp and viable. Variations in the Ca:Mg ratio had little effect on cell yield if the sum of the concentrations of the 2 ions remained the same. Organic as well as inorganic sources of N and P were utilized. NH₄ sources became toxic at elevated levels (7 mg N liter^-1). Methionine was not used as N source. Cells could not be completely depleted of P, but concentrations ≤ 0.01 mg P liter^-1 resulted in poor growth. Vitamin B₁₂, but not thiamine or biotin, was required. Highest cell yields were at a PII-metals concentration of 30 ml liter^-1; a t 100-ml liter^-1 cell yield was very low. Additions (per liter) of Fe (0.5 mg) and Mo (0.1 mg) to the basal medium produced higher cell yields, but Cu (0.1 mg) and V (0.1 mg) inhibited growth.     

Monitoring uptake and contents of Mg,Ca and K in Norway spruce as influenced by pH and Al,using microprobe analysis and stable isotope labelling

In a model system using intact spruce trees (Picea abies [L.] Karst.) we followed the path of magnesium, calcium and potassium during uptake into the root and during long-range transport into the shoot, by multiple stable isotope labelling. The roots of two- and three-year-old spruce trees originating from soil culture were removed from the soil and, in part or in toto, exposed to labelling solutions containing the stable isotopes ²⁵Mg or ²⁶Mg, ⁴¹K and ⁴²Ca or ⁴⁴Ca. Optical-emission-spectroscopy (ICP-OES) of plant fractions and labelling solutions was combined with the quantitative analysis of stable isotope ratios in sections of shock frozen, cryosubstituted material using the laser-microprobe-mass-analyser (LAMMA). This combination allowed us to distinguish, both in bulk samples and on the cellular level between (i) the fraction of elements originally present in the plant before the start of the labelling, (ii) the material taken up from the labelling solution into the plant and (iii) any material released by the plant into the labelling solution.In single-root labelling experiments, roots of three-year-old spruce trees, grown in nursery soil, were exposed to various pH conditions. The exchange of Mg and Ca with the labelling solution was nearly 100% in the cell walls of the mycorrhized finest roots. This exchange was only slightly affected by a step down to pH 3.5. The absolute Mg and Ca content in the cell walls was moderately reduced by incubation at pH 3.5 and strongly reduced in the presence of Al at this pH. After a pH 3.5 and 2 mM Al treatment we found Al in the xylem cell walls and the cortex cell lumina at elevated concentrations. To analyse the combined effect of high Al and high proton concentrations on the long-range transport, we used a split-root system. The root mass of an intact two-year-old spruce tree, grown in mineral soil, was divided into even parts and both halves incubated in solutions with two sets of different stable isotopes of Mg and Ca (side A: no Al, ²⁵Mg and ⁴²Ca; side B: +Al, ²⁶Mg and ⁴⁴Ca) and ⁴¹K on both sides. We observed a large uptake of Mg, Ca and K into the plant and a pronounced release. The net uptake of all three elements was lower from the Al-doted solution. In cross-sections of the apical shoot we found after seven-day labelling period about 60–70% of the Mg and Ca and 30% of the K content in the xylem cell walls originating from both labelling solutions. The clear majority of the Mg and Ca label originated from the Al-doted side.     

Influence of aluminium and nitrogen on uptake and distribution of minerals in beech roots (Fagus sylvatica)

Beech seedlings (Fagus sylvatica L. provenance Västra Torup) were grown in nutrient solution at low pH (4.2) and exposed to AlCl₃ and different concentrations of nitrogen. The effects of AlCl₃ and nitrogen on uptake of Ca²⁺ (⁴⁵Ca) and H₂PO₄ ^- (³²P) in roots of intact beech were studied. Crossections of roots were analyzed with respect to element concentrations, by use of Mikro-PIXE (particle induced X-ray emission). The distribution of Al, Ca, P, Mg, K, and S was analysed. The experiments were designed to evaluate the effects of aluminium on localization of elements in plant root tissue.Aluminium reduced the concentration of Ca in plants and increased that of K. High nitrogen levels in the solution further decreased the concentration of Ca in the roots. Aluminium (1.0 mM) effectively reduced the Ca²⁺ (⁴⁵Ca) uptake in short time experiments. Aluminium accumulated in high concentration (up to 500 mol/g dry weight in areas of 30×30 m²) on the root surface, epidermis and outer layers of cortex. Corresponding areas had an extremely low Ca concentration (ca 5 mol/g dry weight) which could be harmful for regulation of mineral uptake and development of roots.It is concluded that the calcium concentration in roots was reduced by aluminium. The combination with high nitrogen levels further reduced calcium changing the mineral balance which could result in deficiency conditions of calcium in the root.     

The pinus scrub community as an indicator of soils in Hong Kong

Summary Consisting ofPinus massoniana, Rhodomyrtus tomentosa, Baeckea frutescens andDicranopteris linearis, thePinus scrub community is widespread and representative of the vegetation in Hong Kong. Three areas, with soils derived separately from granite, sedimentary and volcanic rocks but of the same pine community were selected for the present study. Soil samples were collected and analysed for pH, texture, organic carbon, total nitrogen, cation exchange capacity, and exchangeable K, Na, Ca, Mg, Fe, Mn, Al and H. Plant samples were also collected for the analysis of K, Na, Ca, Mg, Mn, Al, Fe and SiO₂.While variations in chemical and physical properties exist among the soils of different geology, they are invariably acidic with high exchangeable Al and H ions whereas the base saturation is exceedingly low. Intra- and inter-species variations in chemical composition are equally notable. While K, Mg and Ca are the dominant elements of uptake and accumulation, the fernD. linearis also stands out as a strong accumulator of SiO₂, Al and to some extent, Mn and Fe.     

Retention of added K,Ca and P by Pseudoscleropodium purum growing under an oak canopy

Abstract

Retention of K, Ca and Pby Pseudoscleropodium purum growing under oak in Windsor Forest was examined following treatment, over 9 days, with 10 mol m^?3 CaCl₂ or KH₂PO₄ Concentrations of the added elements and Mg were determined in the intercellular, exchangeable (cell wall) and intracellular fractions of the green tissues before nutrient addition and at intervals (0–205 days) afterwards.

Increases of cations in the intercellular fraction of treated shoots were transient. Addition of K and Ca markedly increased levels of these cations in the exchangeable fraction and significantly reduced the concentration of exchangeable Mg. The changes in exchangeable cations were progressively reversed under field conditions indicating that their levels are in dynamic equilibrium with element concentrations in precipitation and/or throughfall rather than the result of a continuousaccumulation process.

Net uptake of K and Ca into the protoplasts of treated P. purum was slight but substantial net gain (+178%) of P occurred in KH₂PO₄ treated plants. One-third of the additional P was lost within 15 days due, either, to redistribution within the shoot, or, to leakage. Intracellular Mg fell significantly below controls 2 weeks after treatment with CaCl₂ suggesting that Mg uptake involves prior adsorption onto the cell wall exchange sites. Fluctuations in K, Ca and Mg levels of untreated P. purum indicated that appreciable net uptake of natural inputs occurred, particularly during autumn when leachates from the senescing tree canopy may be received.

Element concentrations, including Mg, were highest at a shaded site where the moss remained moist for long periods suggesting that either ion absorption is favoured by protracted contact times or that metabolic nutrient requirement increases with increasingly mesic conditions.     

LUXURY PHOSPHATE UPTAKE AND VARIATION OF INTRACELLULAR METAL CONCENTRATIONS IN HETEROSIGMA AKASHIWO (RAPHIDOPHYCEAE)1

The effectr of phosphate starvation and subsequent uptake on distribution and concentration of phosphate metabolic intermediates and metals were studied in Heterosigma akashiwo (Hada) Hada by ³¹P-NMR spectroscopy, neutron activation analysis and ESR spectroscopy. Excess orthophosphate (4.5 μM P_i, as NaH₂PO₄) added to a medium with P-depleted H. akashiwo cells was rapidly taken up resulting in an increase in P cell quota (q_p)from 68.2 to 99.6 fmol. cell-¹in 2 h and to 156.3 fmol. cell-¹in 6 h. After three days, q_p approached about 190 fmol. cell^?1. Polyphosphate (PP_i) rapidly increased from 0 to 11.4 fmol· cell^?1in 2 h and to 24.7 fmol·cell^?1in 6 h. Diel variation of cell quota indicated that cellular P_i increase was synchronized with cellular PP_i decrease and vice versa. The average chain length of PP_i increased from ca. 0 to ca. 10.2 phosphate residues in 2 h after addition of P_i and one day later, from ca. 9.8 to ca. 12.5. The cell quota of Mn (q_Mn), and to a lesser extent Co, increased rapidly from 4.87 fg. cell^?1in the P- starved condition to 50.48 fg·cell^?12 h afer addition of P_i but decreased to 8.63 fg. Cell^?1by 6 h. Concentrations of Zn, As, Hf, Cu and sometimes Al, Mg, K, and Ca changed in a manner opposite to that of Mn and Co. The excretion of these cations, which was synchronized with the uptake of Mn and Co, may be important for a charge balancing in the cells. The ESR spectra showed that the high cellular Mn observed at 2 h after P addition was Mn²⁺which was taken up by the cells rather than adsorbed on the cell surface. These data combined with PP_i data suggested that the behavior of q_Mn is synchronized with the behavior of average chain length of PP_i.     

丛枝菌根真菌和施加不同形态氮肥对杉木幼苗养分吸收的影响

为了解丛枝菌根真菌(AMF)和不同形态氮对杉木(Cunninghamia lanceolata)生长和养分吸收的影响,以1 a生杉木幼苗接种摩西球囊霉(Glomus mosseae)和添加不同形态氮(NH₄⁺-N和NO₃^–-N),对其养分元素和生长状况的变化进行研究。结果表明,AMF显著提高了杉木的苗高和生物量,促进了杉木对N、P、K、Ca、Mg、Fe和Na的吸收,AMF对微量元素Fe、Na的促进作用总体上要强于大量元素K、Ca。与NO₃^–-N相比,AMF显著提高了NH₄⁺-N处理杉木的生物量、总C和N、Ca、Mg、Mn含量,而且这种显著性在叶中普遍高于根和茎。接种AMF可以促进杉木幼苗的生长和对养分元素的吸收,且添加NH₄⁺-N处理的促进作用要强于NO₃^–-N。     

Effects of Aluminum Exposure on Bone Mineral Density,Mineral, and Trace Elements in Rats

The purpose of the study was to investigate the effects of aluminum (Al) exposure on bone mineral elements, trace elements, and bone mineral density (BMD) in rats. One hundred Wistar rats were divided randomly into two groups. Experimental rats were given drinking water containing aluminum chloride (AlCl₃, 430 mg Al³⁺/L), whereas control rats were given distilled water for up to 150 days. Ten rats were sacrificed in each group every 30 days. The levels of Al, calcium (Ca), phosphorus (P), magnesium (Mg), zinc (Zn), iron (Fe), copper (Cu), manganese (Mn), selenium (Se), boron (B), and strontium (Sr) in bone and the BMD of femur were measured. Al-treated rats showed lower deposition of Ca, P, and Mg compared with control rats. Levels of trace elements (Zn, Fe, Cu, Mn, Se, B, and Sr) were significantly lower in the Al-treated group than in the control group from day 60, and the BMD of the femur metaphysis in the Al-treated group was significantly lower than in the control group on days 120 and 150. These findings indicate that long-term Al exposure reduces the levels of mineral and trace elements in bone. As a result, bone loss was induced (particularly in cancellous bone).     

A comparison of the kinetics of aluminum (Al) uptake and distribution in roots of wheat (Triticum aestivum) using different aluminum sources. A revision of the operational definition of symplastic Al

The lack of information about the movement of aluminum (Al) across the plasma membrane presents a significant barrier to the elucidation of resistance mechanisms which may involve exclusion of Al from the symplast. An understanding of mechanistic aspects of exclusion requires the estimation of symplastic Al levels. Such measurements may be achievable through the use of a kinetic approach. A kinetic protocol was developed to characterize the accumulation and distribution of Al in various cellular compartments in roots of wheat (Triticum aestivum L.). The kinetics of uptake and desorption were similar when Al was supplied as AIK(SO₄)₂ or as AlCl₃. When both salts were supplied at low concentration (50 μM), Al bound to a purified cell wall fraction could be reduced to less than 10–20% of non-exchangeable Al, if roots were washed for 30 min in citric acid following exposure. In contrast, when AlK(SO₄)₂ was supplied at a high concentration (200 μM), a strong linear phase of uptake into cell wall material was observed, which accounted for approximately 48% of non-exchangeable Al in roots. These results suggest that the use of low concentrations of Al in simple salt solutions is required to minimize accumulation of non-exchangeable Al in the apoplasm. A series of multiple-desorption experiments confirmed that citric acid was effective in removing Al from the cell wall compartment of roots exposed to Al for short periods (3 h). However, long exposures (48 h) appeared to create conditions conducive to the accumulation of non-exchangeable Al in the cell wall. In experiments where uptake from solutions containing 50 μM AlCl₃ was followed by desorption in citric acid, non-exchangeable Al in microsomal membrane fractions represented less than 4% of total non-exchangeable Al. Thus, we can exclude the plasma membrane and cell wall as major sites for accumulation of non-exchangeable Al in short exposure studies. Although we cannot provide unequivocal evidence for the localization of Al within the symplast, use of simple salt solutions followed by desorption in citric acid provides the best kinetic technique currently available for the quantitation of Al in the symplasm.     

Aluminium effects on transmembrane potential in cells of fibrous roots of sugar beet

The effect of aluminium (Al) on the electrical transmembrane potential of epidermal and outer cortical root cells of intact seedlings of sugar beet (Beta vulgaris L. cv. Monohill) was studied. The potential difference to the surrounding medium was recorded with microelectrodes inserted into the vacuoles (PD_v) and cytoplasm (PD_c) of intact roots. Both long-term effects of AlCl₃ (100, μM present during cultivation) and immediate effects of AlCl₃ (10, 50, or 100 μM present in the assay medium), were measured. The effect of Al was measured at pH 4.0, 5.0 and 6.5 in order to obtain information on the toxicity of different Al forms existing at different pH values. Low pH and/or the presence of AlCl₃ during cultivation caused large depolarizations of the PD_v. Since the immediate effect of 2,4-dinitrophenol (DNP) on the resting potential of cells from Al-cultivated plants was negligible, it is likely that Al affects the metabolic component of the transmembrane potential. Aluminium also had an immediate effect on the PD in root cells of plants cultivated without Al. Addition of 10 or 50 μM Al to the assay medium caused hyperpolarization of PD_v in the presence of 0.5 mM Ca²⁺ at all pH values studied, depolarization of PD_c at pH 6.5, and hyperpolarization of PD_c at lower pH. At 1 mM Ca²⁺, or in the presence of K⁺ (≥ 2 mM), however, the same Al concentrations had little effect on PD_c. The strongest depolarizing effects of 10 or 50 μM Al in short-term treatments were obtained at pH 6.5, and were probably due to the soluble species Al(OH)₃, which is more frequent at pH 6.5 than at a lower pH. Addition of 50 μM Al caused alkalinization of the root medium at pH 6.5, but not at pH 4.0. Therefore, it is possible that Al at pH 6.5 is bound to, or translocated across, the membrane without the accompanying hydroxide ions. It is likely that most of the Al is bound to the root cells, since removal of Al from the buffer surrounding the roots did not cause the changed PD values to return to the original values. Aluminium also interacts with effects of Ca²⁺ and K⁺ on the membrane potential, since changes in PD, induced by changes in concentrations of Ca²⁺ and K⁺ are different in the absence and presence of Al.     

Effects of six trace metals on calcium fluxes in brown trout (Salmo trutta L.) in soft water

Summary Calcium fluxes were measured simultaneously in brown trout fry maintained in an artificial soft water medium of [Ca] 20 mol·l^-1 and pH 5.6, and exposed to each of six trace metals (Al, Cu, Fe, Ni, Pb, and Zn). The trace metal concentrations represented typical and maximum levels found in acid waters experiencing declining fishery status. In the absence of trace metals, evidence is presented which suggests that ca. 91% of Ca taken up from the external medium was by extraintestinal active transport. Calcium efflux was stimulated by both concentrations of Al, Cu, Fe, and Pb. Efflux was also stimulated by [Ni] 170 nmol·l^-1 and [Zn] 3000 nmol·l^-1. In some cases, response to increased efflux was stimulation of influx. Lack of stimulation of influx resulted in negative net Ca fluxes. Net Ca losses were recorded at both concentrations of Al, Pb, and Ni, lower concentrations only of Fe, and higher concentrations only of Cu and Zn.Abbreviations J _in influx - J _net net flux - J _out efflux Henceforward in this paper, chemical elements are referred to by their chemical symbols rather than by full names     

Uptake of aluminium into Arabidopsis root cells measured by fluorescent lifetime imaging

Background and Aims

Measuring the Al³⁺ uptake rate across the plasma membrane of intact root cells is crucial for understanding the mechanisms and time-course of Al toxicity in plants. However, a reliable method with the sufficient spatial and temporal resolution to estimate Al³⁺ uptake in intact root cells does not exist.

Methods

In the current study, fluorescent lifetime imaging (FLIM) analysis was used to quantify Al³⁺ uptake in the root-cell cytoplasm in vivo. This was performed via the estimation of the fluorescence lifetime of Al–lumogallion {5-chloro-3[(2,4-dihydroxyphenyl)azo]-2-hydroxybenzenesulfonic acid} complexes and measurements of intracellular pH while exposing arabidopsis seedlings to acidic and Al³⁺ stresses.

Key Results

The lifetime of Al–lumogallion complexes fluorescence is pH-dependent. The primary sites for Al³⁺ entry are the meristem and distal elongation zones, while Al³⁺ uptake via the cortex and epidermis of the mature root zone is limited. The maximum rates of Al uptake into the cytoplasm (2–3 µmol m⁻³ min⁻¹ for the meristematic root zone and 3–7 µmol m⁻³ min⁻¹ for the mature zone) were observed after a 30-min exposure to 100 µm AlCl₃ (pH 4·2). Intracellular Al concentration increased to 0·4 µm Al within the first 3 h of exposure to 100 µm AlCl₃.

Conclusions

FLIM analysis of the fluorescence of Al–lumogallion complexes can be used to reliably quantify Al uptake in the cytoplasm of intact root cells at the initial stages of Al³⁺ stress.Key words: Acid stress, Al³⁺, aluminium toxicity, Arabidopsis thaliana, low pH, fluorescent lifetime imaging (FLIM), lumogallion     

Mineral nutrient economy in competing species of Sphagnum mosses

Bog vegetation, which is dominated by Sphagnum mosses, depends exclusively on aerial deposition of mineral nutrients. We studied how the main mineral nutrients are distributed between intracellular and extracellular exchangeable fractions and along the vertical physiological gradient of shoot age in seven Sphagnum species occupying contrasting bog microhabitats. While the Sphagnum exchangeable cation content decreased generally in the order Ca²⁺ ≥ K⁺, Na⁺, Mg²⁺ > Al³⁺ > NH₄ ⁺, intracellular element content decreased in the order N > K > Na, Mg, P, Ca, Al. Calcium occurred mainly in the exchangeable form while Mg, Na and particularly K, Al and N occurred inside cells. Hummock species with a higher cation exchange capacity (CEC) accumulated more exchangeable Ca²⁺, while the hollow species with a lower CEC accumulated more exchangeable Na⁺, particularly in dead shoot segments. Intracellular N and P, but not metallic elements, were consistently lower in dead shoot segments, indicating the possibility of N and P reutilization from senescing segments. The greatest variation in tissue nutrient content and distribution was between species from contrasting microhabitats. The greatest variation within microhabitats was between the dissimilar species S. angustifolium and S. magellanicum. The latter species had the intracellular N content about 40% lower than other species, including even this species when grown alone. This indicates unequal competition for N, which can lead to outcompeting of S. magellanicum from mixed patches. We assume that efficient cation exchange enables Sphagnum vegetation to retain immediately the cationic nutrients from rainwater. This may represent an important mechanism of temporal extension of mineral nutrient availability to subsequent slow intracellular nutrient uptake.     

Mass flow to the root system and mineral uptake of a beech stand calculated from 3-year field data

Summary Mass flow to the root surface is defined here as the concentration of an element in the bulk soil solution times the transpirational water uptake of the plant stand. The ratio of uptake of a mineral element to mass flow is called Mass Flow Coefficient (MFC). From an ecosystem study in a beech forestMFCs for 11 elements have been calculated from 3 years of monthly measurements. They amounted to 0.076, 0.086, 0.34, 0.77, 1.5, 1.7, 2.2, 2.9, 8.3, 11, and 120 for Al, Cl, Na, S, Fe, Mg, Mn, Ca, K, N and P respectively. It is concluded that this stand discriminates against Al, Cl and Na in ion uptake and takes up selectively Mn, Ca, K, N and P while for S, Fe and Mg mass flow transports almost the same amount to the root system as is taken up by the above ground stand.     

Active uptake of aluminium,copper and manganese by the freshwater amphipod Paramelita nigroculus in acidic waters

Experiments were performed on the freshwater amphipod Paramelita nigroculus to determine the route of uptake for Al, Cu and Mn. The extent of correlation between the concentrations of Al, Cu and Mn and those of macro-cations Na, Ca and Mg was investigated in order to determine appropriate strategies of water quality management. Indeed, active uptake of toxicants can be controlled by disturbing the active pump used. After 21 days of exposure to different combined concentrations, survivors were analysed chemically by ICP-S after depuration, drying, ashing and digestion with concentrated nitric acid.The results showed significant correlations between the concentrations of major cations and the three metals under study (i.e. Al, Cu and Mn) at p < 0.05. These are Ca vs Al, Ca vs Mg, Na vs Mg, Na vs Mn, Al vs Mg, Al vs Cu, and Mg vs Mn. No other combination showed significant correlation. High r-values for Na vs Mg (r=0.7194) and for Na vs Mn (r=0.6253), as well as low concentrations of Mg and Mn, suggest interactions between the active uptake of Mn and Mg, although there may be interferences due to the use of Na pump. Additional experiments examined the type of interaction occurring when Mn and Mg were present in 1:1 mixtures in water. The Student's t test showed that observed differences in bioaccumulation of Mn, when alone and when combined, were not statistically significant at p < 0.05. These differences may be attributed to chance but not to the presence of Mg in the medium; while differences in bioaccumulation of Mg, when alone and when combined, were statistically significant at p < 0.002. These were attributed to Mn, which lowers Mg uptake by P. nigroculus.