Soluble Ca Research Articles

Bioaccessibility of As and Pb in orchard and urban soils amended with phosphate, Fe oxide and organic matter

Soils historically contaminated in urban and orchard environments by Pb and As were amended separately with organic matter, soluble Ca phosphate, and Fe oxide to determine whether these materials could lower Pb or As bioaccessibility. After 5 years of equilibration in the laboratory, the amended soils and control were tested for bioaccessibility using the standard physiologically based extraction test (PBET). Bioaccessibilities of Pb and As were not substantially reduced relative to the unamended controls after the 5-year period by any of the soil amendments. Gastric bioaccessibility (GB) of Pb was in all cases much greater than gastrointestinal bioaccessibility (GIB) regardless of soil treatment, whereas GB and GIB of As were similar in magnitude for all soils. Both GB and GIB of Pb were greater in the orchard than the urban soil. Electron microprobe investigations identified discrete particulate forms of Pb in the soils by elemental mapping, and energy dispersive spectrometry (EDS) revealed a frequent spatial association of Pb-rich particles with phosphorus. It is suggested that Pb-rich particles in anthropogenically contaminated soils resist chemical transformation into less labile forms despite thermodynamic favorability because of their low surface area and low solubility. This kinetic effect could explain the observed ineffectiveness of amendments in reducing metal bioaccessibility.

Distribution of Halophyte Plants in Relation to Properties of Salt-Affected Soils of District Thatta

The main objective of this study was to survey and collect some halophyte species capable of growing in highly salt affected soils and their distribution in relation to some soil properties of district Thatta. Sueda fruticosa, Tamarix aphylla, Ceriops candoleana, Cynodon dactylon, and Chenopodum album species were collected form Thatta. Soil samples were collected from the vicinity of each halophyte and were analyzed for pH, organic matter (OM), electrical conductivity (EC), soluble Na+, Ca2+, Mg2+, HCO3-, Cl-, sodium absorption ratio (SAR), and exchangeable sodium percentage (ESP). Halophytes species collected were analyzed for ion (Na+, K+, Ca2+, Mg2+and Cl-) contents. Data regarding plant ionic composition showed that contents of Na+ ranged between 3.7-6.9 %, K+0.7-1.9 ,Ca+2 0.4--1.2 %, Mg2+ 0.6-2.2 and Cl- contents between 0.1-0.8 in species collected from Thatta, respectively. Data further revealed that maximum Na+ (6.9 and %) was recorded in Sueda fruticosa and Salsola indica, highest K+(1.9 %) was noted in Chenopodium album species, greatest Ca+2 (1.2 %) was documented in Sueda fruticosaspecies, highest Mg2+ (2.2 %) was observed in Sueda fruticosa whereas, maximum Cl- (0.8 %) was noted in Sueda fruticosa collected from district Thatta, respectively. Data pertaining to soil properties indicated that EC of studied soils ranged between 7.0-18.4dS m-1, pH 7.5-8.0. O.M 0.82-0.94 % , soluble Ca2+ 17.3-33.3 meq L-1, Mg2+ 15.5-24.6 meq L-1, Na+ 43.6-83.4 meq L-1 , Ka+ 3.20-4.50 meq L-1, HCO3? 2.4-5.3 meq L-1, Cl- 55.6-145.4 meq L-1, SAR 10.2-17.1 whereas, ESP ranged between 12.2-19.6 % in soil samples collected from Thatta, respectively. It was concluded that halophyte species Sueda fruticosa, Tamarix aphylla, gallica, Salsola indica, Cyperus irria accumulate significant amounts of salt (Na+ and Cl-)from salt-affected soil and, therefore, may remediate land to the point where native plants could invade and become established, or the site could be returned to agricultural productivity. These halophytes species have an excellent potential for rehabilitation of degraded salt affected soils.

Vitality fertilization balanced tree nutrition and mitigated severity of Sirococcus shoot blight on mature Norway spruce

The effects of vitality fertilization on needle nutrient status and symptom development of Sirococcus shoot blight (SSB) were examined in a long-term, single-tree fertilization experiment in a 90-yr old Norway spruce stand on acidic soil. Trees showing severe symptoms of SSB (“symptomatic trees”, N=72) and trees with less than 5% of the current-year shoots symptomatic of SBB (“asymptomatic trees”, N=72) were selected among the dominant and co-dominant trees within the stand and randomly assigned to three fertilization treatments: unfertilized control, dolomitic liming and gypsum & kieserite fertilization. Concentrations of macronutrients were determined in healthy current year needles of symptomatic and asymptomatic trees 3 and 6years after fertilization and compared with the status in autumn prior to fertilizer treatment. Severity of SSB was rated yearly from 2001 to 2006 by estimating the percentage of affected current-year shoots in the crown in order to assess evolution of disease severity due to changes of nutritional status of the host.Both fertilizer treatments significantly increased foliar Ca and Mg concentrations, and as a result the primary differences in nutrient status between symptomatic and asymptomatic trees disappeared. Thus, vitality fertilization mitigated insufficient Ca and Mg supply that characterized symptomatic trees prior to fertilization, and balanced tree nutrition. Application of the water soluble Ca- and Mg-fertilizer (gypsum & kieserite-variant) induced a quick but only short-term fertilization effect whereas dolomitic liming resulted in significantly higher Ca and Mg concentrations compared to control 3 as well as 6years after fertilization. In contrast, Ca- and Mg-deficiencies further intensified in the unfertilized trees.Balanced tree nutrition also mitigated disease severity of the fertilized trees and promoted tree recovery, indicating that the elements Ca and Mg are putatively involved in disease tolerance. Best results were achieved by fertilization with a water soluble Ca- and Mg-fertilizer which resulted in an 18.9% reduction of disease severity, assessed by the number of diseased shoots per tree, within five years. While dolomitic liming also promoted tree recovery (reduction in disease severity was 11.8%), in the unfertilized control variant a 3.5% increase was observed in the same period. Reduction in disease severity differed significantly from the control for both fertilizer treatments whereas differences between fertilizer treatments were not significant.Results of this study revealed that balanced nutritional status of mature Norway spruce due to vitality fertilization was associated to reduced symptom development of Sirococcus shoot blight.

Preparation of Dicalcium Phosphate Anhydrous (Monetite) Biological Coating on Titanium by Spray-Drying Method

Titanium and its alloys have been widely used in the manufacture of endosseous implants due to excellent biocompatibility, low elastic modulus, and good chemical stability. However, the titanium based metals are essentially bioinert materials. In order to improve their bioactivity, biological coatings are usually applied. Recent studies found that, compared with hydroxyapatite coating, dicalcium phosphate anhydrous (DCPA, Monetite) coating maybe more bioactive due to higher solubility and release of Ca and P ions. In this work, DCPA coating was prepared through a novel and simple method. Briefly, high concentration DCPA solution was sprayed onto superhydrophilic titanium and the specimens were dried fast in an air-circulating oven. After repeating the process over 100 times, a compact coating was fabricated. The microstructure, chemical composition, wettability, and in vitro bioactivity of the coating were analyzed and evaluated. Results showed that the coating fully covered the substrate and consisted of a large number of uniformly sized DCPA granules that packed together closely. The coating showed good wettability and could keep the property for a long time. After immersion in simulated body fluid for 2 weeks, a large amount of bone-like apatite with low crystallinity was induced implying a good bioactivity.

Physiological, anatomical and antioxidant responses to salinity in the Mediterranean pastoral grass plant Stipa lagascae

Soil and water salinity is a major environmental problem in the dry Mediterranean regions, affecting rangeland production. This study investigated the effects of salinity on the wild perennial grass (Poaceae) species Stipa lagascae R. & Sch., a potential forage plant that could be used to rehabilitate degraded rangelands in dry areas. In a laboratory, 3-month-old S. lagascae seedlings were subjected to increasing salt treatments (0–400 mm NaCl) for 45 days. Physiological and biochemical parameters such as leaf water potential (Ψw), leaf relative water content (RWC), proline, total soluble sugars, Na+, K+ and Ca2+ contents, and catalase, ascorbate peroxidase and glutathione reductase activities were measured. Total soluble sugars and proline concentrations increased and Ψw and RWC decreased with increasing salt concentrations. Lower salt concentrations induced a non-significant degradation of chlorophyll pigments. Shoot Na+ content increased with a salinity level, whereas shoot K+ and Ca2+ concentrations decreased and the K+ : Na+ ratio was lower. The salinity threshold, above which S. lagascae showed signs of damage, occurred at 300 mm. Plants have evolved reactive oxygen species (ROS) scavenging enzymes including catalase, ascorbate peroxidase and glutathione reductase, which provide cells with an efficient mechanism to neutralise ROS. The tolerance strategies of S. lagascae to moderate salinity seem to include osmotic adjustment through total soluble sugars and proline accumulation, and highly inducible antioxidative defence. Further investigations are necessary to study the effect of salt stress on distribution of ions (Na+, K+, Ca2+, Mg2+, Cl–, NO3–, SO42–) and osmotic adjustment. Photosynthesis and water-use efficiency parameters could be also useful tools.

Chemical Bonds of Cations in Grapevine Berries and Stems of Some Important Cultivars of Vitis vinifera (L.) and Their Relevance for Viticulture and Enology

Cations are essential for plant growth, tissue build-up and its stabilization. Divalent cations are necessary for cell wall stability and other interstitial tissues. They may be cross-linked with pectins or form looser ionic bindings. This is of importance for grape processing during the technical operations of juice extraction. Monovalent ions are more involved in vacuolar homeostasis and pH stabilization.With a specific extraction procedure H2O-soluble, 1N NaCl-soluble, 2% CH3COOH-soluble, and 5% HCl-soluble fractions as well as the total content of K, Ca, and Mg were analyzed in grapevine berries and stems. The monovalent K is only found in the water and the NaCl fraction; both in berries and stems. But only 50-60% of the total K can be extracted with both solutes. The divalent cation Ca is found in all four fractions with differing amounts, but water soluble Ca is in most cases highest. Ca may also have an indicator value for BSN, because the water soluble fraction is lowest in the most susceptible variety. Mg is not found in HCl fraction.An analysis of variance shows that the varieties have a significant influence on nutrient distribution in different tissues. It seems that the relation Ca/Mg (NaCl fraction) in stems is a good indicator for BSN because susceptible varieties show lower ratios than resistant ones. Some more research is necessary to clear up this possible relationship.

The effect of waterlogging on electrochemical properties and soluble nutrients in paddy soils

This study was conducted to investigate the influence of waterlogging on availability of nutrients in paddy soils. The five soils were incubated under a waterlogged condition at 30 °C for 12 weeks. The EC, Eh, pH, NH4, K, Na, Ca, Mg, Cl, P, Fe, and Mn of soil solutions were monitored over the waterlogged period. The Eh values generally dropped to the lowest point within 14 days of waterlogging, then increased, and reached equilibrium after 8 weeks of waterlogging. The soil pH decreased in the first 2–4 weeks of waterlogging. The EC values increased partly due to dissolution of soluble salts in the first 2 weeks. The concentrations of soluble NH4 were significantly increased with waterlogging, reached maximum values at week 4–6, and then declined to the initial level. Waterlogging increased the concentration of soluble K, Ca, Mg, Fe, and Mn ions, the magnitudes of changes were greatly affected by soil properties. Increases in soluble Na, K, Ca, and Mg were attributed to the increase in solubility of insoluble salts and increase in competition for the exchange sites. Increases in soluble Fe and Mn induced by waterlogging were attributed to the dissolution of Fe and Mn oxides under reduced conditions.

Acid transformation of bauxite residue: Conversion of its alkaline characteristics

Bauxite residue (BR) is a highly alkaline solid hazardous waste produced from bauxite processing for alumina production. Alkaline transformation appears to reduce the environmental risk of bauxite residue disposal areas (BRDAs) whilst potentially providing opportunities for the sustainable reuse and on-going management of BR. Mineral acids, a novel citric acid and a hybrid combination of acid-gypsum treatments were investigated for their potential to reduce residue pH and total alkalinity and transform the alkaline mineral phase. XRD results revealed that with the exception of andradite, the primary alkaline solid phases of cancrinite, grossular and calcite were transformed into discriminative products based on the transformation used. Supernatants separated from BR and transformed bauxite residue (TBR) displayed distinct changes in soluble Na, Ca and Al, and a reduction in pH and total alkalinity. SEM images suggest that mineral acid transformations promote macro-aggregate formation, and the positive promotion of citric acid, confirming the removal or reduction in soluble and exchangeable Na. NEXAFS analysis of Na K-edge revealed that the chemical speciation of Na in TBRs was consistent with BR. Three acid treatments and gypsum combination had no effect on Na speciation, which affects the distribution of Na revealed by sodium STXM imaging.

Dynamics of soil organic and inorganic carbon in the cropland of upper Yellow River Delta, China.

Soil inorganic carbon (SIC) and organic carbon (SOC) are important carbon reservoirs in terrestrial ecosystems. However, little attention was paid to SIC dynamics in cropland. We conducted a survey in the upper Yellow River Delta of North China Plain. We collected 155 soil samples from 31 profiles, and measured SOC, SIC and soluble Ca2+ and Mg2+ contents. Our results showed that mean SOC content decreased from 9.30 g kg−1 near the surface to 2.36 g kg−1 in 80–100 cm whereas mean SIC content increased from 10.48 to 12.72 g kg−1. On average, SOC and SIC stocks over 0–100 cm were 5.73 kg C m−2 and 16.89 kg C m−2, respectively. There was a significantly positive correlation (r = 0.88, P < 0.001) between SOC and SIC in the cropland. We also found that SIC had a significantly positive correlation with both soluble Ca2+ (r = 0.57, P < 0.01) and Mg2+ (r = 0.43, P < 0.05). Our study suggested that increasing SOC might lead to an increase in SIC stocks in the cropland of North China Plain. This study highlights the importance of SIC in the carbon cycle of China’s semi-arid region.

Dissolution and storage stability of nanostructured calcium carbonates and phosphates for nutrition

Rapid calcium (Ca) dissolution from nanostructured Ca phosphate and carbonate (CaCO3) powders may allow them to be absorbed in much higher fraction in humans. Nanosized Ca phosphate and CaCO3 made by flame-assisted spray pyrolysis were characterized by nitrogen adsorption, X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy. As-prepared nanopowders contained both CaCO3 and CaO, but storing them under ambient conditions over 130 days resulted in a complete transformation into CaCO3, with an increase in both crystal and particle sizes. The small particle size could be stabilized against such aging by cation (Mg, Zn, Sr) and anion (P) doping, with P and Mg being most effective. Calcium phosphate nanopowders made at Ca:P ≤ 1.5 were XRD amorphous and contained γ-Ca2P2O7 with increasing hydroxyapatite content at higher Ca:P. Aging of powders with Ca:P = 1.0 and 1.5 for over 500 days gradually increased particle size (but less than for CaCO3) without a change in phase composition or crystallinity. In 0.01 M H3PO4 calcium phosphate nanopowders dissolved ≈4 times more Ca than micronsized compounds and about twice more Ca than CaCO3 nanopowders, confirming that nanosizing and/or amorphous structuring sharply increases Ca powder dissolution. Because higher Ca solubility in vitro generally leads to greater absorption in vivo, these novel FASP-made Ca nanostructured compounds may prove useful for nutrition applications, including supplementation and/or food fortification.

Managing land application of coal seam water: A field study of land amendment irrigation using saline-sodic and alkaline water on a Red Vertisol

Coal seam (CS) gas operations coproduce water with gas from confined CS aquifers. This CS water represents a potential agricultural resource if the water is able to be chemically amended to comply with management guidelines. Stoichiometric quantities of sulphur and gypsum amendments can be used to neutralise the alkalinity and reduce the sodicity of CS water respectively. These amendments can either be mixed in-line at a water treatment plant or applied directly to land prior to the application of CS water (a practice termed land amendment irrigation - LAI). This study compared the efficacy of LAI with in-line chemical amendment of CS water and irrigation with non-saline, non-sodic and non-alkaline (good quality) water under field conditions in southern Queensland. Soil chemical properties, soluble Ca, Mg, K, Na, electrical conductivity (EC), pH, chloride and alkalinity, as well as saturated hydraulic conductivity were measured to determine the impact of the irrigation treatments on soil chemical and physical conditions. Irrigation of lucerne pasture using solid-set sprinklers applied a total of 6.7 ML/ha of each treatment irrigation water to the experimental plots over a 10-month period. Alkalinity was neutralised using LAI, with no increase in soil alkalinity observed. Soil sodicity did not exceed threshold electrolyte concentration values under either CS water irrigation treatment. Soil chemical and physical properties were comparable for both LAI and in-line chemical amendment of CS water. Soil saturated hydraulic conductivity was maintained under all irrigation treatments. Results showed that the constrained capacity of the irrigation system was unable to meet crop evapotranspiration demand. This resulted in accumulation of salt within the root-zone under the CS water treatments compared to the good quality water treatment. LAI successfully chemically amended Bowen Basin CS water facilitating its beneficial use for agricultural irrigation.

Thermodynamic analysis on calcium dissolution in the system of Ca(II)-NH3-NH4Cl-H2O

ABSTRACTBased on the principles of ionic balance, electro-neutrality and the existing thermodynamic data, the thermodynamics equilibrium on calcium dissolution in the system of Ca(II)-NH3-NH4Cl-H2O was theoretically calculated. The results show that the equilibrium pH values in the system vary from 11.43 to 12.59, and the solubility of Ca(II) is significant in the system of NH4Cl-NH3-H2O. The c(NH4OH) has little influence on c(Ca2+)T and when the ammonia concentration is kept constant, the total calcium concentration (c(Ca2+)T) with a maximum concentration of 2.03 mol/L increases linearly with the increase of concentration of c(NH4Cl). Calcium mainly presents in the form of calcium-bearing complexes instead of calcium ion in the system. The reaction degrees of Ca2+ with ammonium hydroxide and H2O are less in the system. The absolute average error of calcium equilibrium concentration between the experimental and theoretical calculated values is 7.07% in confirmatory experiments. The results are helpful to clarify the leaching behaviour of calcium ions in the system of Ca(II)-NH3-NH4Cl-H2O and provide the theoretical foundation to improve the calcium yield and remove impurities in the leaching stage of the indirect aqueous CO2 sequestration process.

Arrested Sugar Accumulation and Altered Organic Acid Metabolism in Grape Berries Affected by Berry Shrivel Syndrome

Berry samples were collected over four growing seasons from field-grown Cabernet Sauvignon grapevines in the Columbia Valley of southeastern Washington. Shoots were tagged prior to veraison and berries were sampled weekly from the same clusters. Symptoms of berry shrivel (BS) and bunch-stem necrosis (BSN) were monitored through harvest and berry samples were categorized as “healthy,” BS, or BSN for analysis of sugars, organic acids, potassium, and calcium. The vines of four adjacent rows were geolocated using GPS over three years to determine if BS was associated with specific vines or specific locations within the vineyard. Like BSN, the BS syndrome was seemingly restricted to individual clusters rather than individual vines and was spatially unpredictable from year to year. Vines propagated from BS-afflicted shoots only rarely displayed BS symptoms. Ripening-associated changes in berry solutes began simultaneously in healthy and BS clusters at veraison, but accumulation of sugars, K+, and oxalate ceased before shriveling symptoms became apparent on BS clusters. While BS did not affect tartrate, it was associated with slightly faster malate catabolism and slower decrease in soluble Ca2+ than in healthy berries. BS was not only associated with a cessation of phloem inflow into the berries, but also with altered organic acid metabolism and metal cation use.

A preliminary approach of the spatio-temporal distribution of cationic aerosol components in the ambient atmosphere of Kochi, India

Kochi City, situated in the vicinity of the industrial hub and marine niche, is significantly loaded with ionic compounds and get into the atmospheric aerosols which deteriorate the health status of the environment. The distribution of both acid and water extractable cations (Na+, NH4+, K+, Mg2+ and Ca2+) with respect to time and space, in the two phases (I and II) were performed at distinct sites of Kochi, Kerala, India. The study revealed that the water soluble Na+ ion is highlighted in the estuarine site (E1) with momentous load at the coastal site (C1) implying the sea salt influence at these two sites. The average NH4+ and K+ concentration (acid and water soluble fractions) recorded is mostly at the industrial site (R2) which may be endorsed due to the application of NPK fertilizers and also from the process of wood burning sources. Further, K+ is the prominent acid and water soluble cation recorded in the study. Mg2+ ion having both oceanic and anthropogenic origin contributes the present observed pollution load. Average acid soluble Ca2+ content is noted maximum at the estuarine spot E1, where as the hike with respect to water soluble fraction of this ion is noticed at the industrial site, R2. These inferences justify the influence of point sources such as industrial, crustal and construction related activities affecting in and around this metropolis.

Physicochemical parameters, bioactive compounds and microbial quality of sonicated pear juice

SummaryThis study was carried out to investigate the effect of sonication on physicochemical parameters and microorganisms of pear juice. Ultrasound processing of fresh pear juice was done at fixed amplitude [70% (500 W) and frequency (25 kHz) for 0, 15, 30, 45 and 60 min at 25 °C. Total soluble solids, pH, titratable acidity and Ca and Mn remained stable, while the cloud value, ascorbic acid, total phenols, total flavonoids, total antioxidant capacity, sugar contents and Na, K, Fe and Mg showed a significant increase. Decreases in microbial population and P and Cu were also observed. It may be inferred that ultrasound processing for 60 min exhibited optimum results in terms of physicochemical and microbial quality.

Effect of heavy metals on pH buffering capacity and solubility of Ca, Mg, K, and P in non-spiked and heavy metal-spiked soils.

In many parts of the world, soil acidification and heavy metal contamination has become a serious concern due to the adverse effects on chemical properties of soil and crop yield. The aim of this study was to investigate the effect of pH (in the range of 1 to 3 units above and below the native pH of soils) on calcium (Ca), magnesium (Mg), potassium (K), and phosphorus (P) solubility in non-spiked and heavy metal-spiked soil samples. Spiked samples were prepared by cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn) as chloride salts and incubating soils for 40days. The pH buffering capacity (pHBC) of each sample was determined by plotting the amount of H(+) or OH(-) added (mmolkg(-1)) versus the related pH value. The pHBC of soils ranged from 47.1 to 1302.5mmolkg(-1) for non-spiked samples and from 45.0 to 1187.4mmolkg(-1) for spiked soil samples. The pHBC values were higher in soil 2 (non-spiked and spiked) which had higher calcium carbonate content. The results indicated the presence of heavy metals in soils generally decreased the solution pH and pHBC values in spiked samples. In general, solubility of Ca, Mg, and K decreased with increasing equilibrium pH of non-spiked and spiked soil samples. In the case of P, increasing the pH to about 7, decreased the solubility in all soils but further increase of pH from 7, enhanced P solubility. The solubility trends and values for Ca, Mg, and K did not differed significantly in non-spiked and spiked samples. But in the case of P, a reduction in solubility was observed in heavy metal-spiked soils. The information obtained in this study can be useful to make better estimation of the effects of soil pollutants on anion and cation solubility from agricultural and environmental viewpoints.

Water-soluble cations in shoot dry weight of common bean and balance of ions in the soil in response to the magnesium application

ABSTRACTThe increased magnesium (Mg) concentration in vegetables may be reduced due to inter-ionic inhibition caused by the concentration of other water-soluble cations that are mainly associated to low molecular weight organic anions. However, it is not known whether the levels of these compounds in crop residues are modified by increasing the Mg soil application. This study aimed to assess the effects of the Mg application on the contents of water soluble cations [potassium (K+), calcium (Ca2+), magnesium (Mg2+), cooper (Cu2+), iron (Fe2+), manganese (Mn2+), and zinc (Zn2+)] on common bean plant residues. The experiment was conducted under greenhouse conditions with Ustoxix Quatzipsamment in completely randomized design in 4×5 factorial scheme, with three replicates. The treatments consisted of four rates of Mg [0, 50, 100 and 200 mg kg−1, source magnesium chloride (MgCl2)] and five varieties of common bean of the carioca group [BRS Estilo, BRS Ametista, IPR Campos Gerais (CG), IPR Tangará and IAPAR 81]. The Mg rates affected the contents of water soluble Ca2+, Mg2+, Cu2+, Fe2+ and Mn2+ in the extracts of bean residue. The soluble Mg2+ showed a significant correlation with foliar Mg content, indicating the need for further research on the method used to assess nutrient availability in vegetables. The bean varieties showed different responses regarding balance of ions in cation exchange capacity (CEC) and in the Ca/Mg, Ca/K and Mg/K ratios in the soil.

Chemical transformation of CO2 during its capture by waste biomass derived biochars

Biochar is a porous carbonaceous material with high alkalinity and rich minerals, making it possible for CO2 capture. In this study, biochars derived from pig manure, sewage sludge, and wheat straw were evaluated for their CO2 sorption behavior. All three biochars showed high sorption abilities for CO2, with the maximum capacities reaching 18.2–34.4 mg g−1 at 25 °C. Elevating sorption temperature and moisture content promoted the transition of CO2 uptake from physical to chemical process. Mineral components such as Mg, Ca, Fe, K, etc. in biochar induced the chemical sorption of CO2 via the mineralogical reactions which occupied 17.7%–50.9% of the total sorption. FeOOH in sewage sludge biochar was transformed by sorbed CO2 into Fe(OH)2CO3, while the sorbed CO2 in pig manure biochar was precipitated as K2Ca(CO3)2 and CaMg(CO3)2, which resulted in a dominant increase of insoluble inorganic carbon in both biochars. For wheat straw biochar, sorbed CO2 induced CaCO3 transformed into soluble Ca(HCO3)2, which led to a dominant increase of soluble inorganic carbons. The results obtained from this study demonstrated that biochar as a unique carbonaceous material could distinctly be a promising sorbent for CO2 capture in which chemical sorption induced by mineralogical reactions played an important role.

Direct Quantitative Detection of Doc2b-Induced Hemifusion in Optically Trapped Membranes

Ca2+-sensor proteins control the secretion of many neuroendocrine substances. Calcium-secretion coupling may involve several mechanisms. First, Ca2+-dependent association of their tandem C2 domains with phosphatidylserine may induce membrane curvature and thereby enhance fusion. Second, their association with SNARE complexes may inhibit membrane fusion in absence of a Ca2+ trigger. Here we present a method using two optically trapped beads coated with SNARE-free synthetic membranes to elucidate the direct role of the C2AB domain of the soluble Ca2+-sensor Doc2b. Contacting membranes are often coupled by a Doc2b-coated membrane stalk that resists forces up to 600 pN upon bead separation. Stalk formation depends strictly on Ca2+ and phosphatidylserine. Real-time fluorescence imaging shows phospholipid but not content mixing, indicating membrane hemifusion. Thus, Doc2b acts directly on membranes and stabilizes the hemifusion intermediate in this cell-free system. In living cells this mechanism may co-occur with progressive SNARE complex assembly, together defining Ca2+-secretion coupling.

Mobilization of soil-borne arsenic by three common organic acids: Dosage and time effects

A batch experiment was conducted to investigate the mobilization of soil-borne arsenic by three common low-molecular-weight organic acids with a focus on dosage and time effects. The results show that oxalic acid behaved differently from citric acid and malic acid in terms of mobilizing As that was bound to iron compounds. At an equivalent molar concentration, reactions between oxalic acid and soil-borne Fe were kinetically more favourable, as compared to those between either citric acid or malic acid and the soil-borne Fe. It was found that reductive dissolution of soil-borne Fe played a more important role in liberating As, as compared to non-reductive reactions. Prior to the 7th day of the experiment, As mobility increased with increasing dose of oxalic acid while there was no significant difference (P > 0.05) in mobilized As among the treatments with different doses of citric acid or malic acid. The dosage effect on soil-borne As mobilization in the citric acid and malic acid treatments became clear only after the 7th day of the experiment. Soluble Ca present in the soils could cause re-immobilization of As by competing with solution-borne Fe for available organic ligands to form practically insoluble organic compounds of calcium (i.e. calcium oxalate). This resulted in transformation of highly soluble organic complexes of iron (i.e. iron oxalate complexes) into slightly soluble organic compounds of iron (i.e. iron oxalate) or free ferric ion, which then reacted with the solution-borne arsenate ions to form practically insoluble iron arsenates in the latter part of the experiment.