Possible method of aluminium speciation in forest soils

Labile Al forms and species can be a threat in acid soils due to their potential toxicity to plants. However, there is no universally accepted extraction method. Several extraction reagents for Al release from soil have been tested. KCl (0.5 or 1 M) is recommended for extraction of exchangeable Al, while 0.5 or 0.3 M CuCl(2) is suggested for extraction of 'weakly organically bound Al'. Both 0.1 and 0.05 M Na(4)P(2)O(7) are shown to be suitable for the extraction of 'total organically bound Al'. These extractions are relatively simple, robust, and applicable to different soils and soil horizons. In the second part of the paper, detailed speciation of exchangeable soil Al by means of an HPLC instrument equipped with an ion column (IC) is presented. An experimental set-up is described and tested on a set of samples. Interpretation of the speciation results is proposed, based on the separation of Al ions and Al complexes according to their charge. Speciation is shown to be dependent mainly on soil pH and organic matter quality. A general scheme of Al fractionation and speciation in soil is proposed.     

Comparison of Al speciation and other soil characteristics between meadow, young forest and old forest stands

The aim of this paper is to describe the influence of spruce (Picea abies) afforestation on soil chemical properties, especially on soil acidity and aluminium (Al) mobilization and speciation in soil. For our study we used a unique set of three adjacent plots, including a meadow and two spruce forest stands of different age, in otherwise comparable conditions. The plots were located in the region of Giant Mountains, north-eastern Czech Republic. In general, pH values decreased and Al concentrations increased significantly after afforestation. Speciation of KCl-extractable and water-soluble Al in soil samples was done by means of HPLC/IC method. The concentrations of Al(X)¹⁺ and Al(Y)²⁺ forms (in both extracts) are higher in humic and organically enriched (Bhs) horizons. The highest concentration of Al³⁺ in both extracts is in the B horizons of old forest.Generally, in all studied stands majority of Al in aqueous extract is in the Al(X)¹⁺ form, which indicates that a large amount of mobile Al is bound in organic complexes. It suggests that actual toxicity is rather low. On the other hand, we have proved that majority of KCl-extractable Al exists in Al³⁺ form. Thus we can conclude that disturbance of existing equilibrium may cause massive release of highly toxic Al³⁺ from soil sorption complex to the soil solution, and consequently it can endanger the whole ecosystem. Moreover, continuous soil acidification accelerated by anthropogenic factors leading to Al mobilization represents a chemical time bomb.     

Factors controlling spatial distribution of soil acidification and Al forms in forest soils

Soil acidification and Al release in forest soils is controlled by a number of factors, like acid deposition, forest type, parent rock, altitude, etc. This paper studies the principal stand factors affecting spatial distribution of the content of KCl-extractable Al (Al(KCl), mainly exchangeable), Na4P2O7-extractable Al (Al(Na4P2O7), mainly organically bound), and other soil characteristics related to acidification in surface organic (O) and subsurface mineral (B) horizons in the Jizera Mountains region. Geostatistical methods were exploited. The highest Al(KCl) contents in the O horizons were related to high S and N content, low pH and low Ca and Mg content in soil. Liming decreased Al(KCl) contents in the O horizons. Al(Na4P2O7) in the O horizons was more abundant under spruce than under beech; in both horizons it was increased on the immission clear-cut areas populated by grass. Surface horizons are more sensitive to external influence (acid deposition, liming) and their spatial variation is stronger. In the mineral horizons, the effect of pedogenetic processes is more important. The effect of stand factors on Al behaviour is complex and often indirect, mediated for example by organic matter or soil reaction. It is difficult to clearly distinguish the effects of the particular factors.     

Seasonal variation of water extractable aluminium forms in acidified forest organic soils under different vegetation cover

The Jizera Mountains area is affected by natural and anthropogenic acidification processes. The effect of acidification is reflected by presence of elevated amount of different Al forms in soil horizons. Changes of water extractable forms of Al (total $ {\text{Al}}_{{{\text{H}}_{2} {\text{O}}}} $ , species: Al(X)¹⁺, Al(Y)²⁺ and Al³⁺) and other soil characteristics (e.g. DOC, pH) were investigated in forest soils from April to October 2008. Seasonal changes of Al forms were identified in organic F and H soil horizons. No significant effect of the soil type on Al forms was documented. Nevertheless, influence of vegetation cover (beech and spruce forest, clear-cut area) on Al(X)¹⁺, Al(Y)²⁺ forms was proved. The results show that binding and mobility of Al forms are controlled mostly by pH and dissolved organic carbon (DOC).     

Assessment of soil aluminium pools along three mountainous elevation gradients

Anthropogenic soil acidification in mountain forests and consequent Al release still present a significant problem in many regions. The effect of deposition may differ according to stand conditions, including altitude. This contribution is focused on three elevation transects, two in the Jizera Mountains strongly influenced by acid deposition, one in the less affected Novohradske Mountains. Quantification of pools of different Al forms and related soil characteristics (organic carbon, exchangeable hydrogen cations, sorption characteristics, etc.) is evaluated. In the Novohradske Mountains, the pool of both organically bound and water-soluble Al increases with increasing altitudes. In the Jizera Mountains, the distribution is more complicated; it is strongly affected by different forest type (beech vs. spruce), deforestation, and other local differences. Higher amounts of Al are bound in the mineral horizons compared to the surface organic horizons, even in the case of organically bound Al pools. Further differences between different altitudes and between soil horizons in Al distribution were revealed by detailed Al speciation using HPLC/IC method.     

The uptake and speciation of various Al species in the Brassica rapa pekinensis

An investigation was carried out on the uptake and speciation of Al species in Al tolerant Chinese cabbage (Brassica rapa L. ssp. pekinensis). Plants were exposed to 10 microg cm(-3) of Al in the chemical forms of Al3+, Al-citrate and Al-malate in a time span from 1 up to 24 h. In each experiment the nutrient solution and stem sap were analysed by a combination of FPLC ICP AES and ES MS MS techniques. Speciation analysis enabled determination of particular chemical forms of Al present in the nutrient solution or in stem sap. The results indicate that Al3+ added to the nutrient solution remained as Al3+ in the solution during the experiments, but in the roots transformation to Al-malate occurred. Al was transported from roots to the upper parts of the plant as Al-malate (70%) and Al3+ (30%). Al-citrate or Al-malate added to the nutrient solution were transferred to the upper parts of the plant without transformation of their chemical forms.     

Aluminium speciation in the Vienne river on its upstream catchment (Limousin region, France)

The aim of this study was to investigate the speciation of aluminium in the river Vienne on its upstream catchment (Limousin region, France) over a period of seven years (May 1998-September 2004) in order to assess harmful effects on aquatic life. Two sampling points were selected: the first at 4 km from the spring (Peyrelevade), and the second one at 89 km from the spring (Royères). The aluminium speciation was computed with Mineql+ 4.5 speciation software. Organic matter and phosphorous play a major role in aluminium speciation. If we consider the free aluminium ion (Al3+) as being the only toxic form of aluminium, the concentrations of toxic forms recorded at Peyrelevade and Royères were always below the toxic values for fish. However, if the sum of the concentrations of Al3+, Al(OH)2+, Al(OH)2+ and Al(OH)4- is taken into consideration, the concentration of aluminium recorded may have adverse effects on aquatic life in the upstream catchment of the river Vienne. Al(OH)4- is the major contributor to the concentration in toxic aluminium recorded. In general, Al(OH)4- forms appears in water during the summer with water alkalinisation due to an increase in photosynthetic activities.     

Grass cover on forest clear-cut areas ameliorates some soil chemical properties

Clear-cut areas formed after forest decline due to acid deposition, pest attacks, or wind-breaks in temperate mountainous regions are often populated by grass (mainly Calamagrostis villosa). This study focused on the changes of soil chemical characteristics under the grass cover replacing the forest, focusing mainly on aluminium (Al) speciation. Clear-cut area due to strong acid deposition in the Jizera Mountains (Northern Bohemia) was studied. The soils under grass cover exhibit higher pH values and lower exchangeable Al content compared to adjacent surviving forest. Mobile Al species under the grass have larger proportion of non-toxic organic complexes. The content of exchangeable base cations is slightly higher under the grass. The positive effect of grass on soil chemistry was enhanced by liming. The temporary grass cover can therefore improve soil chemical quality for following reforestation. However, the differences are generally limited to surface organic horizons. Similar results were found also on a bark-beetle clear-cut area in the Bohemian Forest (Southern Bohemia) with smaller acid deposition; nevertheless, most differences were not significant there.     

The content of organic carbon and its water-soluble fraction in the soils of Central Evenkia’s post-fire larch associations

The peculiarities of organic carbon water soluble fraction content in the litters and soil profile in burned forests of different age under the cryolithozone conditions have been revealed. It has been shown that surface fires cause a decrease in the content of water-extractable organic carbon (WEOC) in the litters and upper 5 cm deep layer of soil. At the same time in microelevations these differences are more pronounced and the WEOC content in the upper organogenic horizons in burnt-out places is 2 times lower. In the deeper soil horizons there have been no differences detected in the WEOC content between intact plantations and postpyrogenic areas.     

Interactions Between α-Latrotoxin and Trivalent Cations in Rat Striatal Synaptosomal Preparations

The interactions between alpha-latrotoxin (alpha-LTx), a neurosecretagogue purified from the venom of the black widow spider, and the trivalent cations Al3+, Y3+, La3+, Gd3+, and Yb3+ were investigated in rat striatal synaptosomal preparations. All trivalent cations tested were inhibitors of alpha-LTx-induced [3H]dopamine [( 3H]DA) release (order of potency: Yb3+ greater than Gd3+ approximately Y3+ greater than La3+ greater than Al3+). Only with Al3+ could inhibition of [3H]DA release be attributed to a block of 125I-alpha-LTx specific binding to synaptosomal preparations. The inhibitory effect of trivalent ions was reversible provided synaptosomes were washed with buffer containing EDTA. Trivalent ions also inhibited alpha-LTx-induced [3H]DA release at times when alpha-LTx-stimulated release was already evident. alpha-LTx-induced synaptosomal membrane depolarization was blocked by La3+, but not affected by Gd3+, Y3+, and Yb3+. alpha-LTx-stimulated uptake of 45Ca2+ was inhibited by all trivalent cations tested. These results demonstrate that there exist at least three means by which trivalent cations can inhibit alpha-LTx action in rat striatal synaptosomal preparations: (1) inhibition of alpha-LTx binding (Al3+); (2) inhibition of alpha-LTx-induced depolarization (La3+); and (3) inhibition of alpha-LTx-induced 45Ca2+ uptake (Gd3+, Y3+, Yb3+, La3+).     

缙云山森林土壤速效N、P、K时空特征研究

研究了缙云山森林生态系统内4个演替阶段群落的土壤速效N、P、K的时空特性,结果表明：①除灌草丛的速效K外,速效N、P、K含量在不同群落的土壤剖面上均具有明显的层次性,即腐殖质层（A）＞沉积层（B）＞母质层（C）。②A、B两层的速效N、K含量随群落演替方向升高,即灌草丛＜针叶林＜针阔混交林＜常绿阔叶林,速效P含量则为：针叶林＜针阔混交林＜灌草林＜常绿阔叶林。C层速效N、P、K含量似乎与群落演替规律无必然联系。③各群落内A、B层土壤速效N、P、K含量均表现出明显的季节动态,动态规律因元素类型和土壤层次而有差别。     

Geochemical aspects of aluminium in forest soils in Galicia (N.W. Spain)

The aqueous speciation of Al was studied in acid forest soils in N.W. Spain. Aluminum concentrations were 10–70 mol L^–1, with variable proportions oflabile, nonlabile, andacid-soluble Al. Almost all thelabile Al was found complexed with F^–, Al³⁺ concentrations being low. The importance of organic matter was seen in the formation of Al-organic complexes in the solid soil fraction and the presence of aqueous alumino-organic complexes in superficial horizons (umbric epipedons) rich in organic matter.     

Arachidonic acid inhibits thyrotropin-releasing hormone-induced elevation of cytoplasmic free calcium in GH3 pituitary cells

We have shown that arachidonic acid stimulates 45Ca2+ efflux from prelabeled rat pituitary mammotropic (GH3) cells resuspended in "Ca2+-free" medium (Kolesnick, R. N., Mussachio, I., Thaw, C., and Gershengorn, M. C. (1984) Am. J. Physiol. 246, E458-E462). In this study, we further characterize the effects of arachidonic acid on Ca2+ homeostasis in GH3 cells and demonstrate its antagonism of changes induced by thyrotropin-releasing hormone (TRH). At below 5 microM, arachidonic acid stimulated intracellular for extracellular Ca2+ exchange without affecting cell Ca2+ content. Above 5 microM, arachidonic acid decreased membrane-bound Ca2+, as monitored by chlortetracycline, and decreased total cell 45Ca2+ content by depleting nonmitochondrial and mitochondrial pools. However, arachidonic acid did not elevate cytoplasmic free Ca2+ concentration ([Ca2+]i). Arachidonic acid inhibited TRH-induced 45Ca2+ efflux, loss of membrane-bound Ca2+, mobilization of nonmitochondrial Ca2+, and elevation of [Ca2+]i. Arachidonic acid also lowered elevated [Ca2+]i caused by release of mitochondrial Ca2+ with an uncoupler or by influx of extracellular Ca2+ stimulated with K+ depolarization. Hence, arachidonic acid stimulates Ca2+ extrusion from and depletes Ca2+ stores within GH3 cells. We suggest that arachidonic acid may be an important regulator of cellular Ca2+ homeostasis which may inhibit TRH-induced elevation of [Ca2+]i.     

鼎湖山主要森林类型土壤交换性阳离子含量及其季节动态特征

研究鼎湖山自然保护区马尾松林、马尾松荷木混交林和季风常绿阔叶林三种代表性森林类型表层土壤(0~20cm)交换性阳离子含量及其季节动态。结果表明:土壤交换性阳离子含量因元素种类、森林类型和季节不同而异。三种森林土壤交换性阳离子含量都表现为:Al3+>H+>K+>Ca2+、Mg2+、Na+。几乎所有调查的阳离子含量在阔叶林显著高于马尾松林和混交林,但后两者之间大多数阳离子含量差异不显著。鼎湖山森林土壤可交换性阳离子含量虽然较高,但盐基饱和度却很低。马尾松林、混交林和阔叶林土壤可交换性阳离子含量在1997年6月份分别为:58.3、84.5和118.7mmolc/kg,盐基饱和度分别为:5.5%、3.2%和4.5%。三种森林土壤交换性Ca2+、Mg2+、K+和H+含量季节差异极显著(P<0.001),但交换性Al3+含量只在马尾松林土壤存在极显著的季节性差异(P<0.001)。同一元素季节变化大小程度趋向马尾松林>混交林>阔叶林。森林土壤交换性Ca2+、Na+和H+含量与土壤pH值相关关系不明显,但交换性Mg2+、K+和Al3+与土壤pH值间呈极显著负相关。     

Tree Species Effects on Soil Organic Matter Dynamics: The Role of Soil Cation Composition

Abstract We studied the influence of tree species on soil carbon and nitrogen (N) dynamics in a common garden of replicated monocultures of fourteen angiosperm and gymnosperm, broadleaf and needleleaf species in southwestern Poland. We hypothesized that species would influence soil organic matter (SOM) decomposition primarily via effects on biogeochemical recalcitrance, with species having tissues with high lignin concentrations retarding rates of decomposition in the O and A horizons. Additionally, because prior work demonstrated substantial divergence in foliar and soil base cation concentrations and soil pH among species, we hypothesized that species would influence chemical stabilization of SOM via cation bridging to mineral surfaces in the A-horizon. Our hypotheses were only partially supported: SOM decomposition and microbial biomass were unrelated to plant tissue lignin concentrations, but in the mineral horizon, were significantly negatively related to the percentage of the cation exchange complex (CEC) occupied by polyvalent acidic (hydrolyzing) cations (Al and Fe), likely because these cations stabilize SOM via cation bridging and flocculation and/or because of inhibitory effects of Al or low pH on decomposers. Percent CEC occupied by exchangeable Al and Fe was in turn related to both soil clay content (a parent material characteristic) and root Ca concentrations (a species characteristic). In contrast, species influenced soil N dynamics largely via variation in tissue N concentration. In both laboratory and in situ assays, species having high-N roots exhibited faster rates of net N mineralization and nitrification. Nitrification:mineralization ratios were greater, though, under species with high exchangeable soil Ca²⁺. Our results indicate that tree species contribute to variation in SOM dynamics, even in the mineral soil horizons. To our knowledge the influence of tree species on SOM decomposition via cation biogeochemistry has not been demonstrated previously, but could be important in other poorly buffered systems dominated by tree species that differ in cation nutrition or that are influenced by acidic deposition.     

Effect of anion channel antagonists and La3+ on citrate release, Al content and Al resistance in maize roots

The correlation between organic acid anion release and Al content was examined in two maize (Zea mays L.) inbred lines, Cat 100-6 (Al-resistant) and S 1587-17 (Al-sensitive) treated with anion channel antagonists and La3+, a cation channel blocker. In the intact roots of Al-resistant maize, the Al-induced excretion of citrate was inhibited by the anion channel antagonists niflumic acid, anthracene-9-carboxylic and ethacrinic acid. Citrate release in excised root apices was reduced by 60% in the presence of 15 microM niflumic acid, while the Al content increased by 42%. Nevertheless, Cat 100-6 accumulated less Al than S 1587-17 when the rate of citrate release was similar in both lines, indicating that other mechanisms of Al-resistance are operating in Cat 100-6. The presence of 60 microM La3+ did not change the rate of citrate release, but the Al content in excised root apices of Al-resistant plants was reduced by 70%. These results suggest that the Al distributed uniformly in the roots does not contribute to citrate release and possibly the activity of anion channels is correlated with the free activities of extracellular Al3+ close to anion channels.     

ATP receptor. A putative receptor-operated channel in PC-12 cells.

External ATP induces [3H] dopamine [( 3H]DA) release in rat pheochromocytoma cells (PC-12 cells). The ATP-induced release is a saturable process with half-effective concentration of EC50 = 80 microM. ADP is a poor secretagogue of [3H]DA (one-sixth of ATP) and AMP is devoid of secretory capabilities. Adenosine and the non-hydrolyzable analogues of ATP, AppNHp and AppCp are ineffective as inducers of [3H]DA, release, or as inhibitors of the ATP-induced [3H]DA release. The most potent antagonist of ATP-induced release is Coomassie Blue (IC50 = 25 microM), compared to ADP beta S (IC50 = 500 microM). The overall rank order of potency is ATP greater than ADP much greater than AMP greater than adenosine, which is characteristic of the P2-purinergic receptor. ATP-induced secretion is absolutely Ca2+ dependent, indicating an exocytotic process and is independent of Mg2+ (up to 2 mM) suggesting that the active species is not ATP4-. (a) The ATP-induced 45Ca2+ influx into the cells is in good correlation to ATP induction of release (IC50 = 80 and 90 microM, respectively) and is carried over to ADP which has a diminished ability to induce both release and 45Ca2+ influx. (b) Divalent cations (Ba2+ greater than Sr2+ greater than Ln3+ greater than Mn2+) replace Ca2+ and support ATP-induced release similar to their effectiveness in supporting bradykinin- and K+ (50 mM)-induced release in PC-12 cells (Weiss, C., Sela, D., and Atlas, D. (1990) Neurosci. Lett. 119, 241-245). Combined together the absolute requirement of [Ca2+]ex for release, inhibition of release by Gd3+ (IC50 = 100 microM), Ni2+, and Co2+ (IC50 = 1 mM), and support of release by Ba2+, Sr2+, and Mn2+, we suggest that ATP induces Ca2+ entry via ligand-operated Ca2+ channels as previously suggested for ATP in smooth muscle cells (Benham, C.D., Bolton, T.B., Byren, N.G., and Large, W.A. (1987) J. Physiol. (Lond.) 387, 473-488). No significant inhibition by 1 microM verapamil, 10 microM nifedipine, or 2 mM Cd2+ argues against ATP activation of voltage-dependent Ca2+ channels as similarly shown for ATP-induced [3H]noradrenaline release (Inoue, K., Nakazawa, K., Fujimoro, K., and Takanaka, A. (1989) Neurosci. Lett. 106, 294-299). Thus, the widely distributed ATP receptor might play an essential role in Ca2+ homeostasis of the cell by introducing Ca2+ into the cell via specific ligand-gated Ca2+ channels.     

Computer simulation of the distribution of aluminum speciation in soil solutions in equilibrium with the mineral phase imogolite.

The speciation of aluminum (Al) is a critical issue when evaluating the environmental and biological significance of elevated Al concentrations in soil solutions caused by acidic precipitation. Numerous studies have revealed that, with increased concentrations of silica acid in soil, the activity of Al species in soil solutions is greatly modified by SiO(4)(2-). However, thus far there has been little thorough theoretical modeling of this subject. This paper reports a computer simulation of the distribution of Al speciation in soil solutions in equilibrium with the mineral phase imogolite based on a chemical equilibrium calculation. The unique characteristic associated with imogolite reported by previous researchers can be explained theoretically by the proposed model. The dissolved silica has a remarkable influence on Al speciation: increasing concentrations of silica acid may effectively inhibit the formation of polymeric alumino-hydroxo species, and, furthermore, detoxify Al toxicity to plants.     

Soil Solution Chemistry Controlling the Field Distribution of Melica ciliata L.

Germination, establishment and growth of Melica ciliata L.,an 'acidifuge' species of rocky habitats in Europe, were studiedexperimentally and related to chemical properties of the soilsolution, including pH, base cation composition, Al concentrationand speciation, and Mn concentration. M. ciliata failed to establishin acid leptite soil. However, it was able to grow in solutionat pH 3·6 and exhibited vigorous growth at pH 3·9,a typical soil solution pH of leptite sites, which Melica isunable to colonize. Higher concentrations of Mn than those measuredin any leptite soil solutions did not influence growth. Exposureto 0·037 mmol l^-1 (1 mg l^-1) of Al³⁺, a concentrationusually exceeded in the soil solution of leptite sites, severelyretarded root growth. Speciation technique applied to Al insoil solutions obtained by centrifugation demonstrated a closerelationship between H⁺ and Al concentrations and, in particular,between H⁺ and free ionic (quickly reacting) Al species. Soilsolution concentrations of free ionic Al proved to be < 0·002mmol l^-1 in sites lacking Melica , but often > 0·10mmol l^-1 in site lacking Metalica . It is concluded that theinability of M. ciliata to establish in acid soils is not primarilydue to the high H⁺ concentration but to the high soil solutionconcentrations of Al, especially free Al ionic species at lowsoil pH.Copyright 1993, 1999 Academic Press Melica ciliata, distribution, soil solution, pH, aluminium speciation, manganese, base cations, iron     

Characterisation of Ca- and Al-pectate gels by thermal analysis and FT-IR spectroscopy

Thermal analysis (TG-DTA) and FT-IR spectroscopy have been performed on calcium-pectate membranes to investigate their structure and the consequent variation caused by aluminium sorption. Calcium-polygalacturonate (Ca-PG) membranes, model systems of the soil-root interface, were exposed to aluminium solutions at different concentrations (25-800 microM). Three different pHs (3.50, 4.00 and 4.50) were chosen to study the influence of different aluminium species, such as [Al(H2O)6]3+, [Al(OH)(H2O)5]2+ and [Al(OH)2(H2O)(4)]+, on the structure of the Ca-PG membrane. The DTA profiles and FT-IR spectra showed how aluminium sorption induces structural modifications leading to a reorganisation of the chain aggregates and a weakening of the structure. Higher pH, that is, 4.00 and 4.50, and thus hydrolytic aluminium species and related higher calcium content maintain a more regular structure than at pH 3.50. At pH 3.50, both the effect of [Al(H2O)6]3+ and a major calcium release had a greater impact and thus induced a greater weakening of the structure.