Phosphate adsorption and availability plant of phosphate

Summary The effects of phosphate buffer capacity on the plant-availability of labile soil phosphate, when measured as intensity (I) or quantity (Q), are described and tested using results from a greenhouse experiment on 24 Sherborne soils. In multiple regression studies, phosphate buffer capacity with I or Q measurements as independent variables accounted for up to 94% of the variance in P uptake by ryegrass, the maximum buffer capacity being generally more useful than the equilibrium buffer capacity.When the quantity of soil P is measured (Q), its availability (i.e. ease of desorption) to plant roots is inversely related to the Langmuir bonding energy parameter and the buffer capacity. When the intensity of soil P is measured (I), its availability (i.e. resistance to change) is directly related to the adsorption and buffer capacities. The levels of Q or I, therefore, which are optimal for plant uptake vary with the buffer capacity of the soil. There is little or no correlation between the adsorption capacity and the bonding energy in many soils and consequently phosphate buffer capacity is only poorly correlated with the total adsorption capacity.     

Iron content of sediment and phosphate adsorption properties

Phosphorus can occur in sediments in different forms and accordingly its availability varies. The distinction between the phosphorus fractions is made with two chemical extraction methods; an ammonium oxalate-oxalic acid extraction and an extraction according to Hieltjes & Lijklema (1980).The iron and aluminum liberated with the ammonium oxalate-oxalic acid extraction method is linearly correlated (r ² = 0.73) with the phosphorus liberated in the first two steps of the Hieltjes and Lijklema extraction by: P = 0.035 (Fe + Al) + 0.001 (P, Fe and Al in mmol g^–1).The iron and aluminum (hydr)oxides are very important fractions in the sediment adsorption capacity for phosphorus. The phosphorus sorption capacity (PSC) is 0.080 mol P (mol (Fe + Al))^–1 and the adsorption constant (k) is 11.9 µmol P l^–1. Here it is assumed that iron and aluminum (hydr)oxide have the same affinity for phosphorus.     

磷酸盐在土壤中的竞争吸附与解吸机制

本文概述了近年来国内外有关磷酸盐的竞争吸附与解吸的研究成果。土壤中许多阴离子都能与磷竞争吸附点位,使得磷的吸附下降。有机质可促进或抑制磷的吸附,pH是影响竞争吸附的主要因子。磷被吸附后大多固持在表面而难于解吸,往往呈现明显的滞后现象。通常只有拟物理吸附的磷能被解吸,化学吸附的磷因与表面金属离子作用形成双齿配位而极难被淋洗下来。解吸受多种因素的影响,其中解吸剂的类型是主要因子之一。     

Prediction of fertilizer phosphate requirement using the Langmuir adsorption maximum

The phosphate adsorption maximum as calculated by the Langmuir equation was used to predict the fertilizer P requirement of wheat (Triticum aestivium, cv. Caldwell) on both virgin and cultivated Decatur clay loam (clayey, kaolinitic, thermic, Rhodic Paleudult) and Hartsells sandy loam soils (fine-loamy, siliceous, thermic, Typic Hapludult). Soils with higher adsorption maximum were found to require more fertilizer P than soils with lower adsorption maximum. For soils 25% saturation of the adsorption maximum gave the optimum dry matter yield. This corresponded to equilibrium P concentration of 0.45 mg L⁻¹ for Decatur cultivated and 0.31 mg L⁻¹ for Decatur and Hartsells virgin soils for optimum dry matter yield. These values are within the range of those reported previously by other investigators working with different soils.     

光照对水环境变化和沉积物吸收磷酸盐的影响

在富氧和缺氧环境下室内模拟研究光照对清洁湖区沉积物吸收磷酸盐和对上覆水质变化的影响.结果表明,光照使缺氧环境上覆水体中的pH值显著提高,并增加其溶解氧的含量.上覆水体中磷酸盐浓度的变化在实验初期主要受水-沉积物界面溶解氧含量的影响,表现为富氧组磷酸盐的浓度下降迅速,但随实验时间的推移,光照逐渐起主要作用,表现为实验结束时有光条件下的磷酸盐浓度明显低于无光条件,磷酸盐的减少量和减少速度明显高于无光条件.无论是富氧、缺氧,还是有光、无光,当上覆水体中磷酸盐的浓度很高时,沉积物都能够吸收磷酸盐,但吸收量各不相同.光照对沉积物吸收上覆水中溶解性无机磷酸盐(DIP)的影响受缺氧和富氧环境的限制.     

Study on adsorption of Cu(II) by water-insoluble starch phosphate carbamate

Crosslinked starch phosphate carbamates were prepared and used to adsorb Cu(II) ions from an aqueous solution. Scanning electron microscopy (SEM) was used to investigate the changes in the starch granule structure before and after adsorption. Batch adsorption experiments were carried out as a function of adsorption time, adsorbents dose, pH, substitute groups' content, initial Cu(II) ions concentrations, and temperature. The results reveal that 20 min of adsorption time is sufficient for reaching the adsorption equilibrium, the adsorption of Cu(II) ions on crosslinked starch phosphate carbamate is endothermic in nature, and the adsorption equilibrium data correlate well with the Langmuir isotherm model with the maximum adsorption capacity of 1.60 mmol/g. Moreover, the adsorbed Cu(II) ions can be desorbed by treating with HCl solution and the desorption percentage reached above 96% when desorbing with 1 N HCl solution for 1 h.     

Water level fluctuations may decrease phosphate adsorption capacity of the sediment in oligotrophic high mountain lakes

The effect of sediment desiccation and re-wetting on phosphate adsorption and desorption properties was examined in two oligotrophic high mountain lakes (La Caldera and Río Seco, altitude ~3000 m) in the Sierra Nevada National Park, Spain. Decrease in phosphate sorption properties was observed in transects from the littoral zone to dry land (up to the high water mark) in both lakes concomitantly with loss of amorphous oxides of iron and aluminum as revealed by oxalate and dithionite extractions. X-ray diffraction did not indicate increased amounts of crystalline metal oxides, but there was a loss of fine particles (<20 μm) with distance from the shore, probably due to wind erosion. Likely this explains the loss of amorphous metal oxides as they are often enriched in the fine sediment fraction. Changes in P-speciation toward less available pools were also observed as a result of desiccation. When re-wetted under oxic conditions, the sediments, especially those closest to the shore, released phosphate to the overlying water. The loss of adsorption capacity for phosphate upon re-wetting was associated with loss of amorphous iron oxides, and the changes appear to be non-reversible. Thus, both desiccation and re-wetting will lead to a decrease in sediment phosphate sorption capacity and increased water level fluctuations, a possible scenario in climate change, can therefore increase P availability in the water column of these oligotrophic systems.     

Specific adsorption of phosphate ions on proteins evidenced by capillary electrophoresis and reversed-phase high-performance liquid chromatography

Specific adsorption of phosphate ions at pH=7.0 was studied on different proteins, either counter-ions of phosphate (lysozyme, lactoferrin) or co-ion of phosphate (α-lactalbumin). The theoretical electrophoretic mobility of globular proteins lysozyme and α-lactalbumin (apo and holo (+1 calcium per molecule) forms) was compared with those measured by capillary electrophoresis in phosphate at pH 7.0, versus the ionic strength (I) in the range 0–0.775 mol L⁻¹. The specific adsorption of phosphate ions was evidenced by difference. From the experimental charge number (Z^eff) of protein in phosphate medium, a phosphate content per protein molecule was determined at pH=7.0.

• •For lactoferrin (pI=8–9), the electrophoretic mobility (μ) was constant and negative, highlighting a charge reversal due to phosphate adsorption.
• •For α-lactalbumin (holo form) experimental μ was roughly constant and more negative than predicted. Z^eff increased continuously from −4 to −11 in the ionic strength range from 0.005 to 0.775 mol l⁻¹, respectively. Accordingly, one to six phosphates were bound per molecule, respectively.
• •For lysozyme, experimental electrophoretic mobility was positive but lower than predicted. Z^eff was only discrete values +5 for I in the range 0.001–0.020 mol l⁻¹ and about +3 in the range 0.050–0.500 mol l⁻¹, whereas the theoretical Z value was +7 at pH=7.0. Lysozyme bounds one phosphate at low ionic strength and about two — three at higher ionic strength.

Reversed-phase HPLC confirms that adsorption of phosphate is different for the three proteins.     

<Superscript>1</Superscript>H NMR metabonomic study of rat response to tri-phenyl phosphate and tri-butyl phosphate exposure

The industrial application of organophosphates provides the opportunity for environmental exposure. While the toxicity of organophosphate compounds has been the target of significant work, studies directed towards the identification of metabolite markers to assess phosphate exposure are more limited. In this study the urine metabolite profiles for rats following single dose exposure to either tributyl phosphate (TBP, 15 mg/kg body weight) or triphenyl phosphate (TPP, 2 and 20 mg/kg body weight) were characterized using proton nuclear magnetic resonance (¹H NMR) and orthogonal-partial least squares discriminate analysis (O-PLSDA). Using the developed O-PLSDA models it was possible to clearly identify TBP or TPP exposed animals. The performance of these models was validated using cross validation and permutation testing. Utilizing the variable importance in projection (VIP) coefficients from the O-PLSDA the metabolites that were most responsible for the classification of TBP or TPP exposure were determined. This initial study demonstrates the potential for NMR metabonomic studies for the identification and separation of environmental exposure to organophosphates.     

The phosphate transporter gene OsPht1;8 is involved in phosphate homeostasis in rice

Plant phosphate transporters (PTs) are active in the uptake of inorganic phosphate (Pi) from the soil and its translocation within the plant. Here, we report on the biological properties and physiological roles of OsPht1;8 (OsPT8), one of the PTs belonging to the Pht1 family in rice (Oryza sativa). Expression of a β-glucuronidase and green fluorescent protein reporter gene driven by the OsPT8 promoter showed that OsPT8 is expressed in various tissue organs from roots to seeds independent of Pi supply. OsPT8 was able to complement a yeast Pi-uptake mutant and increase Pi accumulation of Xenopus laevis oocytes when supplied with micromolar (33)Pi concentrations at their external solution, indicating that it has a high affinity for Pi transport. Overexpression of OsPT8 resulted in excessive Pi in both roots and shoots and Pi toxic symptoms under the high-Pi supply condition. In contrast, knockdown of OsPT8 by RNA interference decreased Pi uptake and plant growth under both high- and low-Pi conditions. Moreover, OsPT8 suppression resulted in an increase of phosphorus content in the panicle axis and in a decrease of phosphorus content in unfilled grain hulls, accompanied by lower seed-setting rate. Altogether, our data suggest that OsPT8 is involved in Pi homeostasis in rice and is critical for plant growth and development.