Partitioning Of Ca Research Articles

Structural Properties of Casein Micelles with Adjusted Micellar Calcium Phosphate Content.

Micellar calcium phosphate (MCP) content of skim milk was modified by pH adjustment followed by dialysis. Turbidity, casein micelle size and partitioning of Ca and caseins between the colloidal and soluble phases of milk were determined. Protein structure was characterised by Fourier transform infrared (FTIR) spectroscopy and proton nuclear magnetic resonance (1H NMR), whereas organic and inorganic phosphorus were studied by phosphorus-31 nuclear magnetic resonance (31P NMR). The sample with the lowest MCP content (MCP7) exhibited the smallest particle size and turbidity, measuring 83 ± 8 nm and 0.08 ± 0.01 cm-1, respectively. Concentrations of soluble caseins increased with decreasing MCP levels. At ~60% MCP removal, FTIR analysis indicated a critical stage of structural rearrangement and 31P NMR analysis showed an increase in signal intensity for Ca-free Ser-P, which further increased as MCP concentration was further reduced. In conclusion, this study highlighted the importance of MCP in maintaining micellar structure and its impact on the integrity of casein micelle.

Differentiation of Chemical Components in Basaltic Melts During Eruptions: An Example from Tolbachik–Hawaiian Fissure Zones and Etna Vent

The study on differentiation of chemical components in quenched volcanics from the Etna, Tolbachik and Hawaiian fissure zones was carried out under simulated temperature/pressure (T/P) conditions reflecting real-time conditions in the early stages of magmatic eruptions. The simulation was performed under high-pressure chamber apparatus, and the rocks were then subjected to high T/P conditions resulting in basaltic melts. Various temperature and pressure conditions were adjusted from the apparatus to allow for different rates of magmatic cooling and crystallization. The scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS-microanalysis) was then used to study the quenched glasses with the aim of identifying major element partitioning based on micro-heterogeneity of melts structures. The microscopic study of the experimental melts and their comparisons with natural melts under the electron microscopes indicate the existence of two distinct liquids which fractionated during cooling on the basis of their chemical composition (compositional melts): Fe, Mg liquids concentrated in the poorly polymerized and mobile parts of the melt and K, Na and Al liquids were concentrated in more highly polymerized parts of the melts. Partitioning of Ca and Si appears to be changeable and more dependent on bulk melt composition. Fractionation of non-crystalline melts was evident under post-explosion sharp quenching and high-pressure conditions.

Partitioning of Ca to Metastable Precipitates in a Mg-Rare Earth Alloy

Partitioning of Ca to Metastable Precipitates in a Mg-Rare Earth Alloy

Calcium: A comprehensive review on quantification, interaction with milk proteins and implications for processing of dairy products.

Calcium (Ca) is a key micronutrient of high relevance for human nutrition that also influences the texture and taste of dairy products and their processability. In bovine milk, Ca is presented in several speciation forms, such as complexed with other milk components or free as ionic calcium while being distributed between colloidal and serum phases of milk. Partitioning of Ca between these phases is highly dynamic and influenced by factors, such as temperature, ionic strength, pH, and milk composition. Processing steps used during the manufacture of dairy products, such as preconditioning, concentration, acidification, salting, cooling, and heating, all contribute to modify Ca speciation and partition, thereby influencing product functionality, product yield, and fouling of equipment. This review aims to provide a comprehensive understanding of the influence of Ca partition on dairy products properties to support the development of kinetics models to reduce product losses and develop added-value products with improved functionality. To achieve this objective, approaches to separate milk phases, analytical approaches to determine Ca partition and speciation, the role of Ca on protein-protein interactions, and their influence on processing of dairy products are discussed.

Specific arbuscular mycorrhizal fungal–plant interactions determine radionuclide and metal transfer into Plantago lanceolata

Societal Impact StatementIndustrial activity has left a legacy of pollution by radionuclides and heavy metals. The exposure of terrestrial environments to increased levels of ionising radiation and toxic elements is of concern, not only because of the immediate effects to biota but also because of the potential risk of mobilisation into higher levels of a food chain. Here, we present a study that extends our knowledge of how arbuscular mycorrhizal fungi contribute to the mobilisation of non‐essential elements in environments such as former mine sites, and provides a perspective that will be of interest for the management and remediation of such sites.Summary Accumulation and transfer of long‐lived radionuclides and toxic metals in terrestrial environments is of major concern because of potential mobilisation into food chains. In this study, we aimed to compare the role of four different arbuscular mycorrhizal fungal (AMF) cultures on the transfer of non‐essential elements into Plantago lanceolata from a naturally contaminated soil source. Soil from an abandoned uranium (238U) mine was collected as a natural source of 238U, thorium (232Th), arsenic (As) and lead (Pb). P. lanceolata was inoculated with four AMF cultures (Rhizophagus irregularis DAOM181602, Acaulospora longula BEG8, Scutellospora calospora BEG245 and Funneliformis mosseae BEG12) to compare the uptake and transfer from root to shoot. Inductively coupled plasma (ICP) mass spectroscopy and ICP‐absorption emission spectroscopy analyses provided quantification of total elemental concentrations in soil and plant tissues. Two of the AMF cultures, A. longula and F. mosseae, had contrasting roles in toxic element partitioning in plant tissue of P. lanceolata. F. mosseae increased the accumulation of 238U, 232Th, Pb, As and Cu in shoots whereas A. longula induced increased partitioning of 232Th, Ca, Fe and Zn in roots. The inoculation treatments and the differential accumulation of these elements had no significant effect on plant biomass. The use of different AMF cultures in enhancing phytoremediation of contaminated environments requires a wider understanding of the contribution of different AMF cultures to non‐essential element acquisition as well as to plant nutrition.

Global variations of Earth's 520- and 560-km discontinuities

We investigate seismic discontinuities in the mantle transition zone (MTZ) by analyzing SS precursors recorded at global seismic stations. Our observations confirm the global existence of the 520-km discontinuity. Although substantial regional depth variations in the 520-km discontinuity are generally correlated with temperature in the mid-MTZ, they cannot be fully explained by the Clapeyron slope of the wadsleyite-ringwoodite phase transition, suggesting both thermal and compositional heterogeneities in the MTZ. A second discontinuity at ∼560-km depth, previously interpreted as splitting of the 520-km discontinuity, is most commonly detected in cold subduction zones and hot mantle regions. The depth separation between the 520- and 560-km discontinuities varies from ∼80 km in cold regions to ∼40 km in hot areas. The exsolution of calcium-perovskite (Ca-pv) from majorite garnet has been proposed to explain the velocity and density changes across the 560-km discontinuity. However, the gradual exsolution of perovskite and partitioning of Ca and Al between perovskite and garnet appear inconsistent with the relatively “sharp” discontinuity in seismic observations and thus need to be revisited in the future. Nevertheless, because the only known transition in major minerals at this depth in the MTZ is the formation of Ca-pv, the existence of the 560-km discontinuity may imply localized high calcium concentrations in the mid-MTZ possibly related to the recycling of oceanic crust.

Emissions of PM10 from the co-combustion of high-Ca pyrolyzed biochar and high-Si coal under air and oxyfuel atmosphere

The single or co-combustion experiments of high-Ca pyrolyzed biochar and high-Si coal were carried out on a drop tube furnace (DTF) at 1300 °C under air and oxyfuel (CO2:O2=50:50, oxy50) conditions. The produced PM10 (of an aerodynamic diameter of 10 µm or less) was analyzed to investigate the interactions during co-combustion. Due to the characteristics of the selected samples (low S and Cl), the PM1 emissions including PM0.1 and PM0.1–1 are very low during single combustion, except for the PM0.1–1 emission during the combustion of biochar under oxy50 condition because of the massive partitioning of Mg, Ca and Fe. The interaction during co-combustion was observed to mainly occur in the generation of PM1–10, and also slightly occur in the formation of PM0.1–1 under oxy50 condition. The capture of Mg, Ca, and Fe from biochar by the Si-containing minerals in coal under the oxy50 condition results in a slight decrease in PM0.1–1 during co-combustion. The higher the proportion of coal blended, the more obvious the reduction of elements. As for the formation of PM1–10 during co-combustion, high-melting minerals of biochar would weaken the coalescence of minerals in coal to cause more PM10, while the large mineral grains of coal would capture the minerals in biochar to generate more PM10+. Under the competition of the above two types of interactions, the experimental value of PM1–10 yields was almost consistent with the theoretically calculated value, except for blended ratio of 80:20 (coal: biochar, air) or 50:50 (oxy50) with prior interaction predominating.

Emission Behaviors of Inorganic Ultrafine Particles during Zhundong Coal Oxy-Fuel Combustion with Characterized Oxygen Input Fractions Comparable to Air Combustion

Zhundong low-rank coal is very likely to be utilized extensively in oxy-fired boilers in the near future. Its PM10 (particulate matter with an aerodynamic diameter of ≤10 μm) emission behaviors during oxy-fuel combustion need to be carefully studied before its large-scale use. The present study examines the emission behaviors of inorganic ultrafine particles (PM0.5, with an aerodynamic diameter of ≤0.5 μm), as well as PM10 during the combustion of Zhundong coal in air and oxy-fuel conditions (O2/CO2) at three characterized O2 input fractions, i.e., 21, 27 and 32 vol.%. The combustion experiments were carried out in a high-temperature drop-tube furnace (HDTF) at a combustion temperature of 1500 °C. The results show that PM0.5 is composed of Na, S, Mg and Ca, with total fractions of ~90%, while PM0.5–10 (with an aerodynamic diameter between 0.5 and 10 μm) predominantly contains Ca (~50–65%). At three characterized oxygen fractions during oxy-fuel combustion (OXY21, 27 and 32), the promoted O2 fraction was found to increase the yields of both PM0.5 and PM0.5–10. A higher particle-burning temperature and a lower CO2 fraction promote the reactions of both organically bound elements and inorganic minerals, increasing the partitioning of Mg and Ca and causing an increased yield of PM0.5. The yield of PM0.5 from air is high and similar to that from OXY32 while the yield of PM0.5–10 from air is similar to that from OXY27. The high yield of PM0.5 from air is mainly generated by the highest yields of Ca in four conditions.

Assessment of the Tessier and BCR sequential extraction procedures for elemental partitioning of Ca, Fe, Mn, Al, and Ti and their application to surface sediments from Chinese continental shelf

Surface sediments can integrate a wide variety of information of seawater in marginal seas, e.g., the Quaternary sedimentary shelf such as the East China Sea (ECS) and Yellow Sea (YS). The Tessier and BCR sequential extraction procedures (SEPs) have been widely applied for extraction of various geochemical phases from sediments. To choose a suitable SEP for phase extraction of sediments from the above Quaternary sedimentary shelf, efficiency and selectivity experiments were conducted on typical individual minerals and the applicability of each SEP was assessed for natural sediments (the natural sediment standard GSD-9 and three surface sediment samples). The geochemical represented elements (Ca, Fe, Mn, Al, and Ti) were measured using both SEPs. Both SEPs have good dissolution efficiency and selectivity for the targeted geochemical phases; the optimized extractant volume for each fraction was determined. The Tessier SEP is particularly recommended for the study of adsorption-desorption process. The application of the Tessier SEP to surface sediments can furnish valuable information, including the productivity conditions (via the reducible fraction Mn) and sedimentary environments (via the carbonate fraction Ca). These results confirm that the Tessier SEP is suitable for elemental fractionation in sediments from the Chinese continental shelf.

In vitro synthesis of amorphous Mg-, Ca-, Sr- and Ba-carbonates: What do we learn about intracellular calcification by cyanobacteria?

Some cyanobacteria, including Candidatus Gloeomargarita lithophora, which was isolated from Lake Alchichica (Mexico), can form intracellular carbonates. This contradicts the common paradigm that cyanobacterial calcification is always extracellular and suggests that calcification might be controlled by these cyanobacterial species. Intracellular carbonates have several peculiar characteristics: they are relatively small (between 60 and 500nm), they are poorly crystalline, and they have Sr/Ca and Ba/Ca ratios much higher than the solution in which the cells grow. It is therefore crucial to understand whether these unique features may indicate the involvement of specific biological processes. Here, in vitro abiotic syntheses were performed to synthesize Mg-, Ca-, Sr- and Ba-containing carbonates with compositions, crystallinities and sizes close to those observed in intracellularly calcifying cyanobacteria. Precipitates were characterized by scanning and transmission electron microscopies coupled with energy dispersive X-ray spectroscopy, thermogravimetric analysis and X-ray diffraction. The size and the poor crystallinity of cyanobacterial intracellular carbonates could be mimicked under these abiotic conditions. It was shown that similarly to Mg, elements such as Sr and Ba can favor stabilization of poorly crystalline carbonates. In contrast, the differential partitioning of Sr, Ba and Ca between the solution and the solids as observed in cyanobacteria could not be mimicked in vitro. This provides keys to a better understanding of biological processes involved in the formation of intracellular carbonates by some cyanobacteria, including the involvement of membrane transporters.

The role of liquid–liquid immiscibility and crystal fractionation in the genesis of carbonatite magmas: insights from Kerimasi melt inclusions

We have reconstructed the compositional evolution of the silicate and carbonate melt, and various crystalline phases in the subvolcanic reservoir of Kerimasi Volcano in the East African Rift. Trace element concentrations of silicate and carbonate melt inclusions trapped in nepheline, apatite and magnetite from plutonic afrikandite (clinopyroxene–nepheline–perovskite–magnetite–melilite rock) and calciocarbonatite (calcite–apatite–magnetite–perovskite–monticellite–phlogopite rock) show that liquid immiscibility occurred during the generation of carbonatite magmas from a CO2-rich melilite–nephelinite magma formed at relatively high temperatures (1,100 °C). This carbonatite magma is notably more calcic and less alkaline than that occurring at Oldoinyo Lengai. The CaO-rich (32–41 wt%) nature and alkali-“poor” (at least 7–10 wt% Na2O + K2O) nature of these high-temperature (>1,000 °C) carbonate melts result from strong partitioning of Ca (relative to Mg, Fe and Mn) in the immiscible carbonate and the CaO-rich nature (12–17 wt%) of its silicate parent (e.g., melilite–nephelinite). Evolution of the Kerimasi carbonate magma can result in the formation of natrocarbonatite melts with similar composition to those of Oldoinyo Lengai, but with pronounced depletion in REE and HFSE elements. We suggest that this compositional difference results from the different initial parental magmas, e.g., melilite–nephelinite at Kerimasi and a nephelinite at Oldoinyo Lengai. The difference in parental magma composition led to a significant difference in the fractionating mineral phase assemblage and the element partitioning systematics upon silicate–carbonate melt immiscibility. LA-ICP-MS analysis of coeval silicate and carbonate melt inclusions provides an opportunity to infer carbonate melt/silicate melt partition coefficients for a wide range of elements. These data show that Li, Na, Pb, Ca, Sr, Ba, B, all REE (except Sc), U, V, Nb, Ta, P, Mo, W and S are partitioned into the carbonate melt, whereas Mg, Mn, Fe, Co, Cu, Zn, Al, Sc, Ti, Hf and Zr are partitioned into the silicate melt. Potassium and Rb show no preferential partitioning. Kerimasi melt inclusions show that the immiscible calcic carbonate melt is strongly enriched in Sr, Ba, Pb, LREE, P, W, Mo and S relative to other trace elements. Comparison of our data with experimental results indicates that preferential partitioning of oxidized sulfur (as SO4 2−), Ca and P (as PO4 3−) into the carbonate melt may promote the partitioning of Nb, Ta, Pb and all REE, excluding Sc, into this phase. Therefore, it is suggested that P and S enrichment in calcic carbonate magmas promotes the genesis of REE-rich carbonatites by liquid immiscibility. Our study shows that changes in the partition coefficients of elements between minerals and the coexisting melts along the liquid line of descent are rather significant at Kerimasi. This is why, in addition to the REE, Nb, Ta and Zr are also enriched in Kerimasi calciocarbonatites. We consider significant amounts of apatite and perovskite precipitated from melilite–nephelinite-derived carbonate melt as igneous minerals can have high LREE, Nb and Zr contents relative to other carbonatite minerals.

Exogenous Foliar and Root Applications of Abscisic Acid Increase the Influx of Calcium into Tomato Fruit Tissue and Decrease the Incidence of Blossom-end Rot

Plants encounter various environmental stress factors that can potentially impact nutritional requirements and fruit quality. Adequate levels of calcium (Ca) in tomato (Solanum lycopersicum) fruit have positive effects on fruit quality, specifically firmness. One of the results of insufficient Ca uptake and movement in tomato is the physiological disorder blossom-end rot (BER), which is associated with a Ca deficiency in the distal fruit tissue. Previous research has demonstrated that foliar abscisic acid (ABA) applications decreased the incidence of BER and increased the uptake of Ca into fruit tissue. This study examined how root and foliar spray ABA applications, individually and in combination, affect the partitioning of Ca between the leaves and fruit of tomato plants, especially in the distal tissue, and how ABA affects the incidence of BER in the distal tissue of tomato fruit. ‘Mt. Fresh Plus’ tomato were grown in the greenhouse at 25/20 °C (day/night) under a 16-hour photoperiod. Plants were treated with different Ca concentrations in the fertilizer solution. Plants were also treated with foliar spray ABA applications weekly. Calcium was applied through the irrigation lines at 60, 90, or 180 mg·L−1. ABA treatments were applied as a combination of foliar sprays and root applications. Foliar ABA applications, treatments consisted of deionized (DI) water control (0.0 mg ABA/L) or 500 mg ABA/L. For ABA root applications, treatments consisted of a DI water control (0.0 mg ABA/L) or 50 mg ABA/L applied through the irrigation lines. ABA spray treatments were applied once weekly until dripping from the foliage (tops of pots were covered to prevent spray drip into the pot), whereas root applications were applied four times per day through the irrigation system. Fruit tissues were harvested 84 to 90 days after seeding. Fruit tissue was harvested at red ripe maturity and evaluated for yield, BER, and Ca concentrations. Leaves were harvested at the time of fruit and were analyzed for Ca concentrations. The results indicate that a combination of the spray and root applications of ABA resulted in the greatest decrease in BER. The foliar spray application of ABA combined with the Ca treatment of 180 mg·L−1 decreased the incidence of BER. Results also demonstrate that ABA treatments are effective in increasing fruit Ca and preventing BER in the early stages of plant development but are less effective in preventing Ca deficiency in the later stages of growth.

Internal versus external control of calcium nutrition in kiwifruit

AbstractHigher calcium (Ca) concentration in several fleshy fruit including kiwifruit is a pre‐requisite for lower incidence of Ca‐related diseases and improved fruit nutritional value. This review examines the internal and external factors operating along the soil‐to‐fruit pathway that are involved in the uptake and partitioning of Ca in kiwifruit vines. After a brief description of fruit growth and the dynamic of nutrient accumulation during fruit development, the review considers the role of soil Ca concentration and availability, root elongation, mass flow in the apoplast, fruit transpiration, competition between fruit and highly transpiring leaves, weather variables and soil moisture. How fruit morphological and anatomical traits, including skin anatomy, xylem development and hydraulic resistance, influence physiological processes such as transpiration and impact on Ca accumulation is also discussed. The review highlights that approximately 80% of the total Ca content of fruit is accumulated during the early weeks after fruit‐set, suggesting that failure of good fruit Ca nutrition at that time may lead to poor fruit Ca content at harvest. Therefore, based on the analysis of the internal and external factors that influence Ca accumulation, recommendations are made for orchard practices that maximize Ca accumulation in the kiwifruit berry, including optimal pollination, nutrient and irrigation management, and manipulation of canopy architecture.

Further work on experimental plagioclase equilibria and the Skaergaard liquidus temperature

Equilibria between plagioclase and ferrobasaltic melt in low-pressure, dry melting experiments can be demonstrated near the liquidus. Further analyses of melting experiments using optimized beam conditions reveals that previous data for understanding the Skaergaard intrusion potentially suffered from the analytical inclusion of non-equilibrated components in the average plagioclase compositions. New reversal experiments demonstrate convergence between plagioclase rim compositions in melting and crystallization products for a ferrobasaltic melt and thus support equilibrium relations. The new data set provides tighter bounds on experimental plagioclase composition and documents composition-dependent partitioning of Na and Ca between plagioclase and melt. Application of the results to modeling the Skaergaard requires only minor adjustments to the previously proposed liquidus temperatures and liquid line of descent

Flowering dogwood (Cornus florida L.) as mediator of calcium cycling: new insights are revealed by analysis of foliar partitioning

Flowering dogwood (Cornus florida L.) is an important understory tree species that is thought to enhance ecological calcium (Ca) cycling and soil Ca availability through high foliar Ca concentrations and rapid leaf litter decomposition. Calcium is an essential macronutrient in plants, important for stabilizing cell walls and plasma membranes. It is also an ubiquitous intracellular second messenger, helping plants sense and physiologically respond to numerous environmental cues. Analyses of total foliar Ca can be dominated by chemically sequestered Ca, which is not readily available for cellular processes. Thus, analyses of specific foliar partitions of Ca are more closely tied to Ca-dependent processes such as signal transduction. To further develop our understanding of the role of flowering dogwood in ecological Ca cycling, we evaluated foliar Ca partitioning via sequential acidic extractions. We compared Ca partitioning in flowering dogwood to that of white oak (Quercus alba L.), and found significantly more labile Ca in dogwood and a much greater proportion of Ca sequestration in oak. We compared foliar Ca partitioning in white oak at sites with dogwood to that of oaks at dogwood-absent sites, and found significantly greater labile Ca in oaks where dogwood was present. We also investigated the phenological patterns of Ca partitioning and sequestration in flowering dogwood foliage, and found preferential partitioning of Ca into the more labile and physiologically accessible pools throughout the growing season, with minimal Ca sequestration. This work helps elucidate the mechanisms and consequences associated with Ca cycling by flowering dogwood in forested systems.

Liquid immiscibility between silicate, carbonate and sulfide melts in melt inclusions hosted in co-precipitated minerals from Kerimasi volcano (Tanzania): evolution of carbonated nephelinitic magma

The evolution of a carbonated nephelinitic magma can be followed by the study of a statistically significant number of melt inclusions, entrapped in co-precipitated perovskite, nepheline and magnetite in a clinopyroxene- and nepheline-rich rock (afrikandite) from Kerimasi volcano (Tanzania). Temperatures are estimated to be 1,100°C for the early stage of the melt evolution of the magma, which formed the rock. During evolution, the magma became enriched in CaO, depleted in SiO2 and Al2O3, resulting in immiscibility at ~1,050°C and crustal pressures (0.5–1 GPa) with the formation of three fluid-saturated melts: an alkali- and MgO-bearing, CaO- and FeO-rich silicate melt; an alkali- and F-bearing, CaO- and P2O5-rich carbonate melt; and a Cu–Fe sulfide melt. The sulfide and the carbonate melt could be physically separated from their silicate parent and form a Cu–Fe–S ore and a carbonatite rock. The separated carbonate melt could initially crystallize calciocarbonatite and ultimately become alkali rich in composition and similar to natrocarbonatite, demonstrating an evolution from nephelinite to natrocarbonatite through Ca-rich carbonatite magma. The distribution of major elements between perovskite-hosted coexisting immiscible silicate and carbonate melts shows strong partitioning of Ca, P and F relative to FeT, Si, Al, Mn, Ti and Mg in the carbonate melt, suggesting that immiscibility occurred at crustal pressures and plays a significant role in explaining the dominance of calciocarbonatites (sovites) relative to dolomitic or sideritic carbonatites. Our data suggest that Cu–Fe–S compositions are characteristic of immiscible sulfide melts originating from the parental silicate melts of alkaline silicate–carbonatite complexes.

Direct Determination of the Total Concentrations of Magnesium, Calcium, Manganese, and Iron in Addition to their Chemical and Physical Fractions in Dark Honeys

The present work demonstrates a very simple and rapid method for the reliable determination of total concentrations of Mg, Ca, Mn, and Fe in dark honeys by means of flame atomic absorption spectrometry without any special sample pretreatment except for dissolution in water. An analytical scheme for the partitioning of Mg, Ca, Mn, and Fe in analyzed honeys was proposed as well. For a complementary evaluation of fractionation patterns for studied metals, a two linked column solid phase extraction procedure with a nonionic adsorbing resin Amberlite XAD-16 and a strong cation exchange resin Dowex 50 W × 8–200 in addition to an ultrafiltration procedure with five membranes having molecular weight cut-offs of 5, 10, 30, 50, and 100 kDa were used. In the course of the fractionation analysis, it was found that the most dominant group of species is the one containing cationic forms of metals bound to low molecular weight (<5 kDa, 5–10 kDa) natural honey bioligands and is mostly the case of simple ions and labile species of Mg, Ca, Mn, and Fe. Correspondingly, the contribution of the cationic fraction for these metals in analyzed dark honeys was up to 96% (Mg), 95% (Ca), 90% (Mn), and 86% (Fe). A significant contribution of the hydrophobic fraction was also established; it was maximally 10, 18, 20, and 25% for Mg, Ca, Mn, and Fe, respectively.

Impacts of drought on mineral macro- and microelements in provenances of beech (Fagus sylvatica L.) seedlings

Beech seedlings originating from 11 German provenances with different climatic conditions were grown in pots and cultivated in a greenhouse. The composition of macro- and microelements in roots, axes and leaves was measured after half of the seedlings were subjected to a simulated summer drought. The recently described sensitivity of these provenances to drought was compared with drought-mediated changes in the elemental and ionic composition in organs of the seedlings; in addition, partitioning between roots and shoots was evaluated. A number of element concentrations were decreased in roots due to drought (K 94% of control, Mg 94%, Mn 75% and Zn 85%). However, chloride concentration increased in all organs (115-125%) and was the only element affected in leaves. Some changes in ionome can be related to sensitivity of provenances, but it is difficult to decide whether these changes are a result of, or a reason for, drought tolerance or sensitivity. Observed increases in chloride concentration in all plant parts of drought-treated beech seedlings can be explained by its function in charge balance, in particular since the level of phosphate was reduced. As a result of chloride accumulation, the sum of added charges of anions (and cations) in water extracts of leaf and root material was similar between drought and control plants. Since only the partitioning of Ca and Al (both only in axis) as well as Mn was affected and other elements (together with previously observed effects on C, N, S and P) remained unaffected by drought in all provenances, it can be concluded that direct effects by means of mass flow inhibition in xylem and phloem are unlikely. Secondary effects, for example on the pH of transport sap and the apoplastic space, cannot be excluded from the present study. These effects may affect partitioning between the apoplast and symplast and therefore may be significant for drought sensitivity.

Partitioning of Solute to the Primary α-Mg Phase in Creep-Resistant Mg-Al-Ca–Based Cast Alloys

The partitioning of elements during solidification of ternary and quaternary Mg-Al-Ca alloys has been measured by an electron microprobe segregation mapping technique. Differences in the degree of partitioning of Al and Ca to the α-Mg phase in as-solidified MRI230D, AX44, AXJ530, and MRI153M alloys was observed. MRI230D has a higher level of Al and Ca in the primary α-Mg phase, while only a higher level of Al is observed in MRI153M, compared with AX44 and AXJ530. While the increased levels of Al in the MRI alloys may be due in part to higher bulk Al concentrations, the higher level of Ca in the primary phase of MRI230D is attributable to the presence of Sn in this alloy. The differences in the partitioning of Al and Ca to the primary α-Mg phase during solidification influence both solid solution and precipitation strengthening, which can explain observed differences in creep behavior.

Determination of Sr and Ba partition coefficients between apatite from fish ( Sparus aurata) and seawater: The influence of temperature

The Sr/Ca and Ba/Ca ratios in inorganic apatite are strongly dependent on the temperature of the aqueous medium during precipitation. If valid in biogenic apatite, these thermometers would offer the advantage of being more resistant to diagenesis than those calibrated on biogenic calcite and aragonite. We have reared seabreams ( Sparus aurata) in tanks with controlled conditions during experiments lasting for more than 2 years at 13, 17, 23 and 27 °C, in order to determine the variations in Sr and Ba partitioning relative to Ca ( D Sr and D Ba, respectively) between seawater and fish apatitic hard tissues (i.e. teeth and bones), as a function of temperature. The sensitivity of the Sr and Ba thermometers (i.e. ∂ D Sr/∂ T and ∂ D Ba/∂ T, respectively), are similar in bone ( ∂ D b – w Sr /∂ T = 0.0036 ± 0.0003 and ∂ D b – w Ba /∂ T = 0.0134 ± 0.0026, respectively) and enamel ( ∂ D e – w Sr /∂ T = 0.0037 ± 0.0005 and ∂ D e – w Ba /∂ T = 0.0107 ± 0.0026, respectively). The positive values of ∂ D Sr/∂ T and ∂ D Ba/∂ T in bone and enamel indicate that D Sr and D Ba increase with increasing temperature, a pattern opposite to that observed for inorganic apatite. This distinct thermodependent trace element partitioning between inorganic and organic apatite and water highlights the contradictory effects of the crystal-chemical and biological controls on the partitioning of Ca, Sr and Ba in vertebrate organisms. Taking into account the diet Sr/Ca and Ba/Ca values, it is shown that the bone Ba/Ca signature of fish can be explained by Ca-biopurification and inorganic apatite precipitation, whereas both of these processes fail to predict the bone Sr/Ca values. Therefore, the metabolism of Ca as a function of temperature still needs to be fully understood. However, the biogenic Sr thermometer is used to calculate an average seawater temperature of 30.6 °C using the Sr/Ca compositions of fossil shark teeth at the Cretaceous/Tertiary boundary, and a typical seawater Sr/Ca ratio of 0.02. Finally, while the present work should be completed with data obtained in natural contexts, it is clear that Sr/Ca and Ba/Ca ratios in fossil biogenic apatite already constitute attractive thermometers for marine paleoenvironments.