Determination of neo- and D-chiro-inositol hexakisphosphate in soils by solution 31P NMR spectroscopy

Myo-Inositol and D-Chiro-Inositol as Modulators of Ovary Steroidogenesis: A Narrative Review

Myo-inositol is a natural polyol, the most abundant among the nine possible structural isomers available in living organisms. Inositol confers some distinctive traits that allow for a striking distinction between prokaryotes and eukaryotes, the basic clusters into which organisms are partitioned. Inositol cooperates in numerous biological functions where the polyol participates or by furnishing the fundamental backbone of several related derived metabolites, mostly obtained through the sequential addition of phosphate groups (inositol phosphates, phosphoinositides, and pyrophosphates). Overall myo-inositol and its phosphate metabolites display an entangled network, which is involved in the core of the biochemical processes governing critical transitions inside cells. Noticeably, experimental data have shown that myo-inositol and its most relevant epimer D-chiro-inositol are both necessary to permit a faithful transduction of insulin and of other molecular factors. This improves the complete breakdown of glucose through the citric acid cycle, especially in glucose-greedy tissues, such as the ovary. In particular, while D-chiro-inositol promotes androgen synthesis in the theca layer and down-regulates aromatase and estrogen expression in granulosa cells, myo-inositol strengthens aromatase and FSH receptor expression. Inositol effects on glucose metabolism and steroid hormone synthesis represent an intriguing area of investigation, as recent results have demonstrated that inositol-related metabolites dramatically modulate the expression of several genes. Conversely, treatments including myo-inositol and its isomers have proven to be effective in the management and symptomatic relief of a number of diseases associated with the endocrine function of the ovary, namely polycystic ovarian syndrome.

Regulations of myo-inositol homeostasis: Mechanisms, implications, and perspectives

Phosphorylation is the most common module of cellular signalling pathways. The dynamic nature of phosphorylation, which is conferred by the balancing acts of kinases and phosphatases, allows this modification to finely control crucial cellular events such as growth, differentiation, and cell cycle progression. Although most research to date has focussed on protein phosphorylation, non-protein phosphorylation substrates also play vital roles in signal transduction. The most well-established substrate of non-protein phosphorylation is inositol, whose phosphorylation generates many important signalling molecules such as the second messenger IP₃, a key factor in calcium signalling. A fundamental question to our understanding of inositol phosphorylation is how the levels of cellular inositol are controlled. While the availability of protein phosphorylation substrates is known to be readily controlled at the levels of transcription, translation, and/or protein degradation, the regulatory mechanisms that control the uptake, synthesis, and removal of inositol are underexplored. Potentially, such mechanisms serve as an important layer of regulation of cellular signal transduction pathways. There are two ways in which mammalian cells acquire inositol. The historic use of radioactive ³H-myo-inositol revealed that inositol is promptly imported from the extracellular environment by three specific symporters SMIT1/2, and HMIT, coupling sodium or proton entry, respectively. Inositol can also be synthesized de novo from glucose-6P, thanks to the enzymatic activity of ISYNA1. Intriguingly, emerging evidence suggests that in mammalian cells, de novo myo-inositol synthesis occurs irrespective of inositol availability in the environment, prompting the question of whether the two sources of inositol go through independent metabolic pathways, thus serving distinct functions. Furthermore, the metabolic stability of myo-inositol, coupled with the uptake and endogenous synthesis, determines that there must be exit pathways to remove this extraordinary sugar from the cells to maintain its homeostasis. This essay aims to review our current knowledge of myo-inositol homeostatic metabolism, since they are critical to the signalling events played by its phosphorylated forms.

Insight into phytase-producing microorganisms for phytate solubilization and soil sustainability

The increasing demand for food has increased dependence on chemical fertilizers that promote rapid growth and yield as well as produce toxicity and negatively affect nutritional value. Therefore, researchers are focusing on alternatives that are safe for consumption, non-toxic, cost-effective production process, and high yielding, and that require readily available substrates for mass production. The potential industrial applications of microbial enzymes have grown significantly and are still rising in the 21st century to fulfill the needs of a population that is expanding quickly and to deal with the depletion of natural resources. Due to the high demand for such enzymes, phytases have undergone extensive research to lower the amount of phytate in human food and animal feed. They constitute efficient enzymatic groups that can solubilize phytate and thus provide plants with an enriched environment. Phytases can be extracted from a variety of sources such as plants, animals, and microorganisms. Compared to plant and animal-based phytases, microbial phytases have been identified as competent, stable, and promising bioinoculants. Many reports suggest that microbial phytase can undergo mass production procedures with the use of readily available substrates. Phytases neither involve the use of any toxic chemicals during the extraction nor release any such chemicals; thus, they qualify as bioinoculants and support soil sustainability. In addition, phytase genes are now inserted into new plants/crops to enhance transgenic plants reducing the need for supplemental inorganic phosphates and phosphate accumulation in the environment. The current review covers the significance of phytase in the agriculture system, emphasizing its source, action mechanism, and vast applications.

Biochar fertilization effects on soil bacterial community and soil phosphorus forms depends on the application rate

Biochar plays a key role in soil phosphorus (P) forms and distribution by affecting soil biochemical characteristics with relevant effects on the microbial community. In this study, we aimed to study the role of biochar in the variation of microbial community and P forms, and the relationships between soil properties, microbial community, and P forms. Here, we conducted a five-year field experiment NPK minerally fertilized with different application rates of biochar; control (B0, 0 kg ha^-1 yr^-1), low rate (B1500, 1500 kg ha^-1 yr^-1), medium rate (B3000, 3000 kg ha^-1 yr^-1), high rate (B6000, 6000 kg ha^-1 yr^-1). Our study showed that the highest increases in bacterial diversity and abundances coincided with increases in P forms typically retained in bacterial cells (β-glucosidase, adenosine monophosphate-AMP, choline phosphate, and glucose-6 phosphate) and occurred at medium application rates. At low application rates, N₂-fixing and P solubilizing and mineralizing bacteria (Sphingomonas, Haliangium, and Bradyrhizobium) increased. P forms retained in bacterial cells decreased at the highest application rates while the most stable forms such as DNA and inositol hexaphosphate (IHP), steadily increased. Stereoisomers of IHP derived from soil microbes (scyllo-IHP and D-chiro-IHP) accounted for the total IHP increases at high application rates. pH and available P and K and total P were highest at high biochar application rates whereas the proportion of organic P was reduced. The most relevant genus in such soils was Gemmatimonas, a polyphosphate accumulating and pyrogenic material degrading bacterium. Therefore, it appears that applying biochar at higher rates reduced the abundance of plant growth promoting bacteria while enhancing the abundance of P accumulating and pyrogenic degrading types.

Direct observation of humic acid-promoted hydrolysis of phytate through stabilizing a conserved catalytic domain in phytase

As a potential phosphorus (P) pool, the enzymatic hydrolysis of organic phosphorus (P_o) is of fundamental importance due to the release of bioavailable inorganic phosphate (P_i) for agronomic P sustainability. However, little is known about the role of soil organic matter (SOM) in the hydrolysis process of phytate by phytase and the subsequent chemical behaviors involving the hydrolysis product (P_i) at different soil interfaces. Here, by using liquid-cell atomic force microscopy (AFM), we present a model system to in situ quantify the nucleation kinetics of phytase-released P_i when precipitating with representative soil multivalent cations (Ca²⁺/Fe³⁺) on typical soil mineral/organic interfaces in the presence/absence of humic acid (HA), which involves complex phytase-interface-HA interactions. We observed that a higher HA concentration resulted in a faster nucleation rate of amorphous calcium/iron phosphate (ACP/AIP) on bare and organically-coated (-OH/-COOH) mica surfaces compared with the HA-free control. Besides, the nucleation rate of ACP/AIP induced by organic interfaces was much more significant than that induced by clay mineral interfaces. By combining enzyme activity/stability experiments and AFM-based PeakForce quantitative nanomechanical mapping (PF-QNM) measurements, we directly quantified the contribution of noncovalent phytase-HA interaction to the increase in enzymatic activity from complex phytase-interface-HA interactions. Furthermore, the direct complexation of phytase-HA resulted in the stabilization of a conserved active catalytic domain (ACD) in phytase through the enhanced formation of both an ordered, stereochemically-favored catalytic domain and an unordered non-catalytic domain, which was revealed by Raman secondary structure determination. The results provide direct insights into how HA regulates the catalytic activity of phytase controlling P_o fates and how soil interfaces determine the behaviors of released P_i to affect its availability, and thereby contribute to P sustainability in soils.

Enhancing Phytate Availability in Soils and Phytate-P Acquisition by Plants: A Review

Phytate (myo-inositol hexakisphosphate salts) can constitute a large fraction of the organic P in soils. As a more recalcitrant form of soil organic P, up to 51 million metric tons of phytate accumulate in soils annually, corresponding to ∼65% of the P fertilizer application. However, the availability of phytate is limited due to its strong binding to soils via its highly-phosphorylated inositol structure, with sorption capacity being ∼4 times that of orthophosphate in soils. Phosphorus (P) is one of the most limiting macronutrients for agricultural productivity. Given that phosphate rock is a finite resource, coupled with the increasing difficulty in its extraction and geopolitical fragility in supply, it is anticipated that both economic and environmental costs of P fertilizer will greatly increase. Therefore, optimizing the use of soil phytate-P can potentially enhance the economic and environmental sustainability of agriculture production. To increase phytate-P availability in the rhizosphere, plants and microbes have developed strategies to improve phytate solubility and mineralization by secreting mobilizing agents including organic acids and hydrolyzing enzymes including various phytases. Though we have some understanding of phytate availability and phytase activity in soils, the limiting steps for phytate-P acquisition by plants proposed two decades ago remain elusive. Besides, the relative contribution of plant- and microbe-derived phytases, including those from mycorrhizas, in improving phytate-P utilization is poorly understood. Hence, it is important to understand the processes that influence phytate-P acquisition by plants, thereby developing effective molecular biotechnologies to enhance the dynamics of phytate in soil. However, from a practical view, phytate-P acquisition by plants competes with soil P fixation, so the ability of plants to access stable phytate must be evaluated from both a plant and soil perspective. Here, we summarize information on phytate availability in soils and phytate-P acquisition by plants. In addition, agronomic approaches and biotechnological strategies to improve soil phytate-P utilization by plants are discussed, and questions that need further investigation are raised. The information helps to better improve phytate-P utilization by plants, thereby reducing P resource inputs and pollution risks to the wider environment.

Preparation of nano-ferrous sulfide modified with phytate for efficient Cr(VI) removal in aqueous solutions

Phytate-modified nano-ferrous sulfide (IP₆-nano-FeS) was successfully prepared to overcome the low efficiency of heavy metal removal by nano-ferrous sulfide (nano-FeS) due to the agglomeration and easy oxidization of this reducing agent. The results showed that IP₆-nano-FeS improved the dispersion of nano-FeS particles, and the maximum Cr(VI) removal reached 436.94 ± 25.40 mg/g. A more novel contribution of this study is that Cr(VI) removal by IP₆-nano-FeS was enhanced in the presence of Mg²⁺, Ca²⁺, and O₂. The removal efficiency increased by ∼10% and ∼8.5% in the presence of conventional cations (Mg²⁺ and Ca²⁺: 2-10 g/L) and O₂, respectively. The application potential of IP₆-nano-FeS for the rapid removal of Cr(VI)-contamination in the presence of aerobic and coexisting cations was confirmed in this study.

Effect of phytic acid and morphology on Fe (oxyhydr)oxide transport under saturated flow condition

Phytic acid (myo-inositol hexaphosphate, IHP) is a dominant form of organic phosphate (OP) in organic carbon-rich surface soil. The IHP impact on Fe (oxyhydr)oxide transport is critical for iron and phosphorus (bio)geochemical processes in iron and phosphorus rich soil and subsurface systems. Three typical Fe (oxyhydr)oxides (ferrihydrite, hematite, and goethite) were studied in this research. The effects of IHP and morphology on Fe (oxyhydr)oxide transport and IHP cotransport had been investigated using saturated sand columns. The results showed that IHP significantly enhanced the mobility of Fe (oxyhydr)oxide by 30-90% due to the stronger electrostatic repulsion. At low IHP concentration (< 50 µM IHP), the rod-like goethite and goethite-facilitated IHP showed high mobility due to their orientation and motion along the water flow, which is 70% faster than ferrihydrite and hematite at pH 5 and 90% faster at pH 10. The mobility of amorphous ferrihydrite was slowest among three selected iron oxides (< 37% at pH 5 and < 72% at pH 10). At high IHP concentration (> 50 μM IHP), the surface precipitation might have occurred on ferrihydrite because of its poorly ordered crystallinity, contributing to its less negatively charged surface and weak transport. The new insight provided in this study is essential for evaluating the fate and transport behavior of iron and iron-facilitate OP in soil rich in iron and OP.

Land use and landscape position influence soil organic phosphorus speciation in a mixed land use watershed

Land use can significantly alter soil P forms, which will influence P loss in runoff. Organic P (P_o ) compounds are an important component of soil P, but their forms and cycling in soils with different land uses are still poorly understood. In addition, streambanks are potential sources of P loss; P forms and concentrations in streambank soils may vary with land use, affecting potential P loss to water. This study used solution ³¹ P nuclear magnetic resonance spectroscopy to characterize and quantify P in interior and streambank soils (0-10 cm) under duplicate sites from four different land uses along streams in the Missisquoi River basin (VT, USA): silage corn, hay meadow, emergent wetlands, and forest. Orthophosphate monoesters were the dominant P compound class regardless of land use or landscape position. Forest soils had the lowest P_o concentrations, less labile P forms than other soils, and significantly lower concentrations of total inositol hexakisphosphates and total orthophosphate monoesters compared with corn soils. Riparian buffer zones for agricultural soils lowered P concentrations in streambank soils for many soil P pools relative to interior soils. The wetland soils of this study had P concentrations and P forms that were similar to those for interior agricultural soils and generally showed no reduction in P concentrations in streambank soils relative to interior soils. This is consistent with the role of wetlands as P sinks in the landscape but also suggests these wetlands should be carefully monitored to minimize P accumulation, especially in streambank soils.

Role of plant growth promoting bacteria in driving speciation gradients across soil-rhizosphere-plant interfaces in zinc-contaminated soils

Inoculation of soil or seeds with plant growth promoting bacteria ameliorates metal toxicity to plants by changing metal speciation in plant tissues but the exact location of these changes remains unknown. Knowing where the changes occur is a critical first step to establish whether metal speciation changes are driven by microbial metabolism or by plant responses. Since bacteria concentrate in the rhizosphere, we hypothesised steep changes in metal speciation across the rhizosphere. We tested this by comparing speciation of zinc (Zn) in roots of Brassica juncea plants grown in soil contaminated with 600 mg kg^-1 of Zn with that of bulk and rhizospheric soil using synchrotron X-ray absorption spectroscopy (XAS). Seeds were either uninoculated or inoculated with Rhizobium leguminosarum bv. trifolii and Zn was supplied in the form of sulfide (ZnS nanoparticles) and sulfate (ZnSO₄). Consistent with previous studies, Zn toxicity, as assessed by plant growth parameters, was alleviated in B. juncea inoculated with Rhizobium leguminosarum. XAS results showed that in both ZnS and ZnSO₄ treatments, the most significant changes in speciation occurred between the rhizosphere and the root, and involved an increase in the proportion of organic acids and thiol complexes. In ZnS treatments, Zn phytate and Zn citrate were the dominant organic acid complexes, whilst Zn histidine also appeared in roots exposed to ZnSO₄. Inoculation with bacteria was associated with the appearance of Zn cysteine and Zn formate in roots, suggesting that these two forms are driven by bacterial metabolism. In contrast, Zn complexation with phytate, citrate and histidine is attributed to plant responses, perhaps in the form of exudates, some with long range influence into the bulk soil, leading to shallower speciation gradients.

Novel Substrates for Kinases Involved in the Biosynthesis of Inositol Pyrophosphates and Their Enhancement of ATPase Activity of a Kinase

IP6K and PPIP5K are two kinases involved in the synthesis of inositol pyrophosphates. Synthetic analogs or mimics are necessary to understand the substrate specificity of these enzymes and to find molecules that can alter inositol pyrophosphate synthesis. In this context, we synthesized four scyllo-inositol polyphosphates-scyllo-IP₅, scyllo-IP₆, scyllo-IP₇ and Bz-scyllo-IP₅-from myo-inositol and studied their activity as substrates for mouse IP6K1 and the catalytic domain of VIP1, the budding yeast variant of PPIP5K. We incubated these scyllo-inositol polyphosphates with these kinases and ATP as the phosphate donor. We tracked enzyme activity by measuring the amount of radiolabeled scyllo-inositol pyrophosphate product formed and the amount of ATP consumed. All scyllo-inositol polyphosphates are substrates for both the kinases but they are weaker than the corresponding myo-inositol phosphate. Our study reveals the importance of axial-hydroxyl/phosphate for IP6K1 substrate recognition. We found that all these derivatives enhance the ATPase activity of VIP1. We found very weak ligand-induced ATPase activity for IP6K1. Benzoyl-scyllo-IP₅ was the most potent ligand to induce IP6K1 ATPase activity despite being a weak substrate. This compound could have potential as a competitive inhibitor.

Phosphorus-based metabolic pathway tracers in surface waters

Trophic status in surface waters has been mostly monitored by measuring soluble reactive phosphorus (SRP) and total phosphorus (TP). Additional to these common parameters, a two-dimensional ion chromatography mass spectrometry (2D-IC-MS) method was used to simultaneously measure soluble phosphate (Pi), pyrophosphate (PPi), and eleven phosphate-containing metabolites (P-metabolites) in Lake Ontario and its tributaries. From the additional P species, PPi, adenosine 5'-monophosphate (AMP), glucose 6-phosphate (G-P), D-fructose 6-phosphate (F-P), D-fructose 1,6-biphosphate (F-2P), D-ribulose 5-phosphate (R-P), D-ribulose 1,5-bisphosphate (R-2P), and D-(-)-3-phosphoglyceric acid (PGA) were detected and quantified in the lake and river samples. The additional multivariate statistical analysis identified similarities between samples collected at different locations. The presence of R-P, R-2P, and F-2P in Lake Ontario tributaries seems to be mainly related to the Calvin cycle, while the lack of all these three P-metabolites and higher PGA levels than G-P in Toronto Harbour samples seems to be the result of depleted Calvin cycle, pentose phosphate, and glycolysis metabolic pathways.

Accessing Legacy Phosphorus in Soils

Repeated applications of phosphorus (P) fertilizers result in the buildup of P in soil (commonly known as legacy P), a large fraction of which is not immediately available for plant use. Long-term applications and accumulations of soil P is an inefficient use of dwindling P supplies and can result in nutrient runoff, often leading to eutrophication of water bodies. Although soil legacy P is problematic in some regards, it conversely may serve as a source of P for crop use and could potentially decrease dependence on external P fertilizer inputs. This paper reviews the (1) current knowledge on the occurrence and bioaccessibility of different chemical forms of P in soil, (2) legacy P transformations with mineral and organic fertilizer applications in relation to their potential bioaccessibility, and (3) approaches and associated challenges for accessing native soil P that could be used to harness soil legacy P for crop production. We highlight how the occurrence and potential bioaccessibility of different forms of soil inorganic and organic P vary depending on soil properties, such as soil pH and organic matter content. We also found that accumulation of inorganic legacy P forms changes more than organic P species with fertilizer applications and cessations. We also discuss progress and challenges with current approaches for accessing native soil P that could be used for accessing legacy P, including natural and genetically modified plant-based strategies, the use of P-solubilizing microorganisms, and immobilized organic P-hydrolyzing enzymes. It is foreseeable that accessing legacy P will require multidisciplinary approaches to address these limitations.

Purification of the phytase enzyme from Lactobacillus plantarum: The effect on pansy growth and macro-micro element content

In the present study, the phytase enzyme was purified from Lactobacillus plantarum with a 3.08% recovery, 9.57-purification fold, and with a specific activity of 278.82 EU/mg protein. Then, the effects of the 5 EU and 10 EU purified phytase was determined on the plant growth, quality, the macro-micro nutrient content of pansy (Viola × wittrockiana), which is of great importance in ornamental plants industry. The research was established under greenhouse conditions with natural light in 2017. The pansy seeds were coated with phytase enzyme solution, sown in a peat environment, and transferred to pots at the seedling period. In general, the 5 EU and 10 EU applications increase plant height, the number of leaves per plant, the number of side branches per plant, and flower height parameters compared to control. Also, micro- and macronutrient values in soil and plant samples were examined. According to the results, the phytase application on pansy cultivation positively affected the properties and yielded high quality of plants.

Effects of suspended particular matters, excess PO43-, and salinity on phosphorus speciation in coastal river sediments

Phosphorus (P) is an essential biogenic element in aquatic ecosystem, and its speciation in sediment may influence the water quality. The composition of P in suspended particular matters (SPM) and sediments were analyzed. Metal ions bonding PO₄^3- and chelating organic P (OP) were explored by Visual MINTEQ simulation and infrared spectroscopy. Inorganic P (IP) mainly comprises orthophosphate and pyrophosphate in SPM. OP mainly includes α-glycerol phosphate, β-Gly, monophosphate, and mononucleotides from aquatic plants in SPM. Cyclotella, Nitzschia, Amphiprore, and terrestrial C₃ plants are the main source of aquatic plants in JH, while they are from Oscillatoria and Merismopedia in JL. These aquatic plants directly determine whether OP or IP is taken to surface sediments during the setting of SPM. The bonding between PO₄^3- and Ca is more preferential than Al and Fe, so the excess PO₄^3- makes Ca compounds bonding IP (Ca-IP) and Al/Fe/Mn (hydr) oxides associated IP (Al/Fe/Mn-IP) dominant, but limited PO₄^3- preferentially contributes more Ca-IP. Metal ions in saline water can firmly cheat with OP via P-OH and/or P=O groups to promote the burial of OP.

Molecular-level investigations of effective biogenic phosphorus adsorption by a lanthanum/aluminum-hydroxide composite

Biogenic phosphorus (P), such as organic P and inorganic pyrophosphates, could substantially contribute towards eutrophication in aquatic systems by internal loading of P from sediment through P species transformation. Previous eutrophication management studies mainly focus on the removal of orthophosphate (Ortho-P), however, an effective approach for biogenic P control from water sources, prior to incorporation in sediment, is still lacking. In this study, a lanthanum/aluminum-hydroxide (LAH) composite was demonstrated to provide both superior removal of Ortho-P and biogenic P, employing myo-inositol hexakisphosphate (IHP) and pyrophosphate (Pyro-P) as model compounds. The maximum IHP and Pyro-P adsorption capacities by LAH attained 36.4 and 21.8 mg P g^-1, respectively. In order to understand the mechanisms of adsorption, zeta potential, ³¹P solid-state nuclear magnetic resonance (NMR) spectroscopy and P K-edge X-ray absorption near edge structure (XANES) techniques were used to characterize the LAH after adsorption. The results supported the hypothesis that the interaction between LAH and P species was through surface adsorption, by the formation of inner-sphere complexes. Linear combination fitting results of XANES data indicated that IHP and Pyro-P preferentially bonded with La-hydroxide in LAH. This study elucidates the adsorption properties and binding mechanisms of IHP and Pyro-P on lanthanum-bearing compounds at the molecular level, indicating that LAH is a promising material for the control of eutrophication.

Quantitative measures of myo-IP6 in soil using solution 31P NMR spectroscopy and spectral deconvolution fitting including a broad signal

Inositol phosphates, particularly myo-inositol hexakisphosphate (myo-IP6), are an important pool of soil organic phosphorus (P) in terrestrial ecosystems. To measure concentrations of myo-IP6 in alkaline soil extracts, solution 31P nuclear magnetic resonance (NMR) spectroscopy is commonly used. However, overlap of the NMR peaks of myo-IP6 with several other peaks in the phosphomonoester region requires spectral deconvolution fitting (SDF) to partition the signals and quantify myo-IP6. At present, two main SDF approaches are in use; the first fits a Lorentzian/Gaussian lineshape to the myo-IP6 peaks directly to the baseline without an underlying broad signal, and the second fits a Lorentzian/Gaussian lineshape to the myo-IP6 peaks simultaneously with an underlying broad peak. The aim of this study was to compare the recovery of added myo-IP6 to soil extracts using both SDF procedures for six soil samples of diverse origin and differing concentrations of organic P (112 to 1505 mg P per kgsoil). The average recovery of total added myo-IP6 was 95% (SD 5) and 122% (SD 32) using SDF with and without an underlying broad signal, respectively. The recovery of individual peaks of myo-IP6 differed, most notably, the C5 phosphate peak of myo-IP6 was overestimated by up to 213% when a broad peak was not included in SDF. Based on the SDF procedure that includes a broad peak, concentrations of myo-IP6 ranged from 0.6 to 90.4 mg P per kgsoil, which comprised 1-23% of total phosphomonoesters. Our results demonstrate that the SDF procedure with an underlying broad signal is essential for the accurate quantification of myo-IP6 in soil extracts.

Can soil phosphorus availability in tropical forest systems be increased by nitrogen-fixing leguminous trees?

Understanding the role of N-fixing leguminous trees for phosphorus (P) cycling in highly weathered tropical soils is relevant for the conservation of natural forests as well as the sustainable management of agroforests and forest plantations with low P input in the Brazilian Atlantic Forest region. We hypothesized that N-fixing leguminous trees can increase the availability of soil P by exploiting different P sources without causing a depletion of soil organic P due to efficient biogeochemical cycling, but empirical evidence remains scarce. For this purpose, ³¹P nuclear magnetic resonance spectroscopy (³¹P NMR) was used for quantifying soil P forms and the Hedley sequential extraction to determine soil P fractions. The studied sites were forestry systems with leguminous trees: mixed forest plantations with different proportions of fast-growing N-fixing leguminous trees; pure plantations, and agroforestry systems with leguminous trees. The results show that all N-fixing leguminous trees and N mineral fertilization positively affected the concentrations of available soil P in relation to the control treatments. There were increases of all P fractions through cycling in all forest sites. ³¹P NMR spectra clearly identified and quantified that a large amount of phosphomonoesters followed by phosphodiesters in the form of DNA, as well as high reserves of P_i species (ortho-P and pyrophosphate) in the first eleven years of growth at pure plantations, mixed plantations or agroforests. The relations between both ortho-P and DNA with the resin-P_i, NaHCO₃-P_i and NaOH-P_i fractions suggest that both analysis methods provide complementary information about the soil P transformations. Thus, the paper highlights the importance of the use of different N-fixing leguminous tree species under different environmental conditions, production systems and management practices for recovering heavily degraded areas, which may be a suitable strategy through efficient management of P in highly weathered tropical soils in the Brazilian Atlantic Forest biome.

Land use change from permanent rice to alternating rice-shrimp or permanent shrimp in the coastal Mekong Delta, Vietnam: Changes in the nutrient status and binding forms

Saline water intrusion has become a severe threat in the coastal areas of Mekong delta of Vietnam, though offering farmers the option to diversify their land use, and switching, for instance, from permanent rice to alternating rice-shrimp systems or even to permanent shrimp systems. The objective of this study was to evaluate the respective impacts on soil salinity, nutrient status and their binding forms. Hence, we sampled the topsoils (cultivation layer, 0-15 cm) from 10 permanent rice systems and the rice platforms of 10 alternating riceshrimp systems. Furthermore, the sludges and the soils 10 cm underneath of the sludges from the ditches of the alternating rice-shrimp as well as from ponds of the permanent shrimp systems were sampled in Bến Tre and Sóc Trăng provinces, Vietnam, respectively. The samples were analyzed regarding their electric conductivity, total and plant-available nutrient contents. To reveal possible changes in nutrient binding forms, sequential P and S extraction, 31P-nuclear magnetic resonance spectroscopy, and S and P X-ray absorption near edge structure spectroscopy were applied. The results showed that permanent and alternating shrimp cultivation lead to elevated salt concentrations but also improved the overall nutrient status relative to the permanent rice management and especially in the sludges relative to the soils underneath. The continued deposition of shrimp and feed debris promoted the accrual of stable, Ca- and Mg-associated P forms as well as of P-monoesters, whereas the S forms were depleted in thiophene S groups but enriched in sulfides relative to permanent rice fields. As effects by alternating rice-shrimp management were intermediate, this management has more potential to serve as a no-regret strategy for farmers to remain flexible in their response to climate changes and concurrent salinity intrusion relative to permanent shrimp production, which requires strict maintenance of adequate salinity levels also during the rainy season.

Effects of macro metals on alkaline phosphatase activity under conditions of sulfide accumulation

Alkaline phosphatase (AP) is commonly found in aquatic ecosystems as an extracellular enzyme closely related to the biogeochemical cycling of phosphorus. Although the AP activity (APA) is conventionally thought to be a main response to PO₄^3- starvation, significant effects of macro metal elements (Al, Fe, and Ca) and S on the APA were found in this study. The APA was reduced by Al primarily through the adsorption of the enzyme onto AlOOH colloids. Fe²⁺ inhibited the APA via a mechanism involving free radical oxidation. The main mechanism by which Ca²⁺ inhibited the APA was by competing with Mg²⁺ and Zn²⁺ for the active sites of the enzyme. Excessive S^2- could reduce the APA by removing Zn²⁺ from the active sites of the enzyme. The inhibition of APA could be reversed if some metal ions (e.g., Fe²⁺) were precipitated by S^2- under reducing conditions. Therefore, in anaerobic ecosystems, the effects of macro metals on APA under conditions of sulfide accumulation may have innovative implications for phosphorus management.

Redox-dependent phosphorus burial and regeneration in an offshore sulfidic sediment core in North Yellow Sea, China

Phosphorus (P) pollution can trigger severe marine eutrophication, which further leads to harmful algal blooms, and a deterioration of sea water quality. The P burial and regeneration in offshore sediments can directly affect the eutrophication levels of estuarine and coastal ecosystems. Although many researches on redox-dependent P burial and regeneration were studied, such process in the presence of silicate is still poorly understood, and the effects of pyrite formation on organic P (OP) burial and regeneration also remain unclear. In this study, a sulfidic sediment core was collected in the offshore of an estuary in the north Yellow Sea, China. Results indicated that indigenous biological input was found to be the primary source of organic matter in upper sediments. The regenerated P under reducing conditions was dominated by labile FeP and OP. The PO₄^3- released from FeP and OP that could be captured by Al/Fe/Mn (oxyhydr) oxides in surface sediments and Ca minerals in deep sediments. CaP, AlP, unreactive Al/Fe-Si-P and some stable metal chelated OP were the main burial P fractions. Sulfate reduction and formation of insoluble metal sulfides including the pyrite promoted OP decomposition by anaerobic decomposition, removing metal ions from the "metal-OP" chelates and restoring the phosphatase activity.

Isolation of Inositol Hexakisphosphate from Soils by Alkaline Extraction and Hypobromite Oxidation

Inositol hexakisphosphates are extracted from soil in strong alkali and isolated from other organic phosphates by hypobromite oxidation. The procedure yields the four stereoisomeric forms of inositol hexakisphosphate in a form suitable for spectroscopic or chromatographic identification.

Effects of myo-inositol hexakisphosphate, ferrihydrite coating, ionic strength and pH on the transport of TiO2 nanoparticles in quartz sand

Evaluating the fate and transport of nanoparticles (NPs) in the subsurface environment is critical for predicting the potential risks to both of the human health and environmental safety. It is believed that numerous environmental factors conspire to control the transport dynamics of nanoparticles, yet the effects of organic phosphates on nanoparticles transport remain largely unknown. In this work, we quantified the transport process of TiO₂ nanoparticle (nTiO₂) and their retention patterns in water-saturated sand columns under various myo-inositol hexakisphosphate (IHP) or phosphate (Pi) concentrations (0-180 μM P), ferrihydrite coating fractions (λ, 0-30%), ionic strengths (1-50 mM KCl), and pH values (4-8). The transport of nTiO₂ was enhanced at increased P concentration due to the enhanced colloidal stability. As compared with Pi at the equivalent P level, IHP showed stronger effect on the electrokinetic properties of nTiO₂ particles due to its relatively more negative charge and higher adsorption affinity, thereby facilitating the nTiO₂ transport (and thus reduced retention) in porous media. At the IHP concentration of 5 μM, the retention of nTiO₂ increased with increasing λ and ionic strength, while decreased with pH. In addition, the retention profiles of nTiO₂ showed a typical hyperexponential pattern for most scenarios mainly due to the unfavorable attachment, and can be well described by a hybrid mathematical model that coupled convection dispersion equations with a two-site kinetic model and DLVO theory. These quantitative estimations revealed the importance of IHP on affecting the transport of nTiO₂ typically in phosphorus-enriched environments. It provides new insights into advanced understanding of the co-transport of nanoparticles and phosphorus in natural systems, essential for both nanoparticle exposure and water eutrophication.

A synthetic cyclitol-nucleoside conjugate polyphosphate is a highly potent second messenger mimic

Reactions that form sec-sec ethers are well known, but few lead to compounds with dense functionality around the O-linkage. Replacement of the α-glucopyranosyl unit of adenophostin A, a potent d-myo-inositol 1,4,5-trisphosphate (IP3R) agonist, with a d-chiro-inositol surrogate acting substantially as a pseudosugar, leads to "d-chiro-inositol adenophostin". At its core, this cyclitol-nucleoside trisphosphate comprises a nucleoside sugar linked via an axial d-chiro-inositol 1-hydroxyl-adenosine 3'-ribose ether linkage. A divergent synthesis of d-chiro-inositol adenophostin has been achieved. Key features of the synthetic strategy to produce a triol for phosphorylation include a new selective mono-tosylation of racemic 1,2:4,5-di-O-isopropylidene-myo-inositol using tosyl imidazole; subsequent conversion of the product into separable camphanate ester derivatives, one leading to a chiral myo-inositol triflate used as a synthetic building block and the other to l-5-O-methyl-myo-inositol [l-(+)-bornesitol] to assign the absolute configuration; the nucleophilic coupling of an alkoxide of a ribose pent-4-ene orthoester unit with a structurally rigid chiral myo-inositol triflate derivative, representing the first sec-sec ether formation between a cyclitol and ribose. Reaction of the coupled product with a silylated nucleobase completes the assembly of the core structure. Further protecting group manipulation, mixed O- and N-phosphorylation, and subsequent removal of all protecting groups in a single step achieves the final product, avoiding a separate N6 protection/deprotection strategy. d-chiro-Inositol adenophostin evoked Ca2+ release through IP3Rs at lower concentrations than adenophostin A, hitherto the most potent known agonist of IP3Rs.

A Fluorescent Probe Identifies Active Site Ligands of Inositol Pentakisphosphate 2-Kinase

Inositol pentakisphosphate 2-kinase catalyzes the phosphorylation of the axial 2-OH of myo-inositol 1,3,4,5,6-pentakisphosphate for de novo synthesis of myo-inositol hexakisphosphate. Disruption of inositol pentakisphosphate 2-kinase profoundly influences cellular processes, from nuclear mRNA export and phosphate homeostasis in yeast and plants to establishment of left-right asymmetry in zebrafish. We elaborate an active site fluorescent probe that allows high throughput screening of Arabidopsis inositol pentakisphosphate 2-kinase. We show that the probe has a binding constant comparable to the K_m values of inositol phosphate substrates of this enzyme and can be used to prospect for novel substrates and inhibitors of inositol phosphate kinases. We identify several micromolar K_i inhibitors and validate this approach by solving the crystal structure of protein in complex with purpurogallin. We additionally solve structures of protein in complexes with epimeric higher inositol phosphates. This probe may find utility in characterization of a wide family of inositol phosphate kinases.

Long-Term Land Use Affects Phosphorus Speciation and the Composition of Phosphorus Cycling Genes in Agricultural Soils

Agriculturally-driven land transformation is increasing globally. Improving phosphorus (P) use efficiency to sustain optimum productivity in diverse ecosystems, based on knowledge of soil P dynamics, is also globally important in light of potential shortages of rock phosphate to manufacture P fertilizer. We investigated P chemical speciation and P cycling with solution ³¹P nuclear magnetic resonance, P K-edge X-ray absorption near-edge structure spectroscopy, phosphatase activity assays, and shotgun metagenomics in soil samples from long-term agricultural fields containing four different land-use types (native and tame grasslands, annual croplands, and roadside ditches). Across these land use types, native and tame grasslands showed high accumulation of organic P, principally orthophosphate monoesters, and high acid phosphomonoesterase activity but the lowest abundance of P cycling genes. The proportion of inositol hexaphosphates (IHP), especially the neo-IHP stereoisomer that likely originates from microbes rather than plants, was significantly increased in native grasslands than croplands. Annual croplands had the largest variances of soil P composition, and the highest potential capacity for P cycling processes based on the abundance of genes coding for P cycling processes. In contrast, roadside soils had the highest soil Olsen-P concentrations, lowest organic P, and highest tricalcium phosphate concentrations, which were likely facilitated by the neutral pH and high exchangeable Ca of these soils. Redundancy analysis demonstrated that IHP by NMR, potential phosphatase activity, Olsen-P, and pH were important P chemistry predictors of the P cycling bacterial community and functional gene composition. Combining chemical and metagenomics results provides important insights into soil P processes and dynamics in different land-use ecosystems.

Simple synthesis of 32P-labelled inositol hexakisphosphates for study of phosphate transformations

BACKGROUND AND AIMS

In many soils inositol hexakisphosphate in its various forms is as abundant as inorganic phosphate. The organismal and geochemical processes that exchange phosphate between inositol hexakisphosphate and other pools of soil phosphate are poorly defined, as are the organisms and enzymes involved. We rationalized that simple enzymic synthesis of inositol hexakisphosphate labeled with 32P would greatly enable study of transformation of soil inositol phosphates when combined with robust HPLC separations of different inositol phosphates.

METHODS

We employed the enzyme inositol pentakisphosphate 2-kinase, IP5 2-K, to transfer phosphate from [γ-32P]ATP to axial hydroxyl(s) of myo-, neo- and 1D-chiro-inositol phosphate substrates.

RESULTS

32P-labeled inositol phosphates were separated by anion exchange HPLC with phosphate eluents. Additional HPLC methods were developed to allow facile separation of myo-, neo-, 1D-chiro- and scyllo-inositol hexakisphosphate on acid gradients.

CONCLUSIONS

We developed enzymic approaches that allow the synthesis of labeled myo-inositol 1,[32P]2,3,4,5,6-hexakisphosphate; neo-inositol 1,[32P]2,3,4,[32P]5,6 - hexakisphosphate and 1D-chiro-inositol [32P]1,2,3,4,5,[32P]6-hexakisphosphate. Additionally, we describe HPLC separations of all inositol hexakisphosphates yet identified in soils, using a collection of soil inositol phosphates described in the seminal historic studies of Cosgrove, Tate and coworkers. Our study will enable others to perform radiotracer experiments to analyze fluxes of phosphate to/from inositol hexakisphosphates in different soils.

Simulated bioavailability of phosphorus from aquatic macrophytes and phytoplankton by aqueous suspension and incubation with alkaline phosphatase

Bioavailability of phosphorus (P) in biomass of aquatic macrophytes and phytoplankton and its possible relationship with eutrophication were explored by evaluation of forms and quantities of P in aqueous extracts of dried macrophytes. Specifically, effects of hydrolysis of organically-bound P by the enzyme alkaline phosphatase were studied by use of solution ³¹P-nuclear magnetic resonance (NMR) spectroscopy. Laboratory suspensions and incubations with enzymes were used to simulate natural releases of P from plant debris. Three aquatic macrophytes and three phytoplankters were collected from Tai Lake, China, for use in this simulation study. The trend of hydrolysis of organic P (P_o) by alkaline phosphatase was similar for aquatic macrophytes and phytoplankton. Most monoester P (15.3% of total dissolved P) and pyrophosphate (1.8%) and polyphosphate (0.4%) and DNA (3.2%) were transformed into orthophosphate (14.3%). The major forms of monoester P were glycerophosphate (8.8%), nucleotide (2.5%), phytate (0.4%) and other monoesters P (3.6%). Proportions of P_o including condensed P hydrolyzed in phytoplankton and aquatic macrophytes were different, with the percentage of 22.6% and 6.0%, respectively. Proportion of P_o hydrolyzed in debris from phytoplankton was approximately four times greater than that of P_o from aquatic macrophytes, and could be approximately twenty-five times greater than that of P_o in sediments. Thus, release and hydrolysis of P_o, derived from phytoplankton debris would be an important and fast way to provide bioavailable P to support cyanobacterial blooming in eutrophic lakes.

Diffusion-Ordered Nuclear Magnetic Resonance Spectroscopy (DOSY-NMR): A Novel Tool for Identification of Phosphorus Compounds in Soil Extracts

Liquid-state, one-dimension ³¹P nuclear magnetic resonance spectroscopy (NMR) has greatly advanced our understanding of the composition of organic phosphorus in the environment. However, the correct assignment of signals is complicated by overlapping and shifting signals in different types of soils. We applied therefore for the first time diffusion-ordered spectroscopy (DOSY) to soil extracts, allowing us to separate phosphorus components in the second domain based on their translational diffusion coefficients. After successful application to a mixture of 14 model compounds, diffusion rates correlated closely with the molecular weight of the individual compound in aqueous solution (R² = 0.97). The method was then applied to NaOH/EDTA extracts of a grassland soil, of which paramagnetic contaminations were removed with sodium sulfide following high-velocity centrifugation (21 500g, 45 min) at 4 °C. Diffusion rates in soil extracts were again closely related to molecular weight (R² = 0.98), varying from 163.9 to 923.8 Da. However, our DOSY application failed for a forest soil with low organic phosphorus content. Overall, DOSY did help to clearly identify specific NMR signals like myo- and scyllo-inositol hexakisphosphate. It thus provides a more confident signal assignment than 1D ³¹P NMR, although currently the ubiquitous use of this novel methodology is still limited to soils with high organic phosphorus content.

Overestimation of orthophosphate monoesters in lake sediment by solution 31P-NMR analysis

Solution ³¹P nuclear magnetic resonance spectroscopy (³¹P-NMR) is a useful method for analyzing organic phosphorus (P_o). Unfortunately, the extraction conditions, which are highly alkaline and require long extraction times, make this analysis less effective. In this research, according to the lability of orthophosphate monoesters (mono-P_o) and orthophosphate diesters (diesters-P_o), we verified the hypothesized overestimation of mono-P_o in lake sediment using solution ³¹P-NMR. We set three scenes to redistribute the mono-P_o and diesters-P_o. Six components, including eight mono-P_o species, were detected in the NaOH-EDTA extracts of sediment samples using ³¹P-NMR. The results showed that mono-P_o (212.7 mg kg^-1) was the dominant P_o in the surface sediment. In the three scenes, mono-P_o decreased from 212.7 to 112.0 mg kg^-1, and diesters-P_o increased from 31.9 to 132.7 mg kg^-1. The ratio of mono-P_o to diesters-P_o increased from 6.7 to 0.8. Therefore, we deduced that the concentration of mono-P_o was overestimated, while that of diesters-P_o was underestimated, in most research because of the high pH and long extraction process. Diesters-P_o might be an important labile P source during the P "exhausted" period.

Long-term Changes in Grassland Soil Phosphorus with Fertilizer Application and Withdrawal

Long-term phosphorus (P) applications can increase soil P concentrations in excess of agronomic optima, posing a risk to water quality. Once fertilization stops, however, it may take time for soil P concentrations to decline. Whereas P fertilization adds orthophosphate, little is known about changes in other soil P forms during P buildup and drawdown. This study examined changes in P pools (total P, Olsen P, Mehlich P, and water-extractable P) and P forms determined by P-nuclear magnetic resonance spectroscopy (P-NMR) in grazed grassland plots from Northern Ireland. Between 1994 and 1999, all plots received 8.3 kg P ha yr with variable rates of nitrogen (100-500 kg N ha yr). From 2000 to 2005, plots received 0, 20, 40, or 80 kg P ha yr and 250 kg N ha yr; from 2005 to 2010, no P fertilizer was applied to any plots. In 2005, soil P pool concentrations at the highest P fertilization rates were significantly elevated compared with those in 2000 but had decreased to 2000 concentrations by 2010. In soils receiving no P, soil P pool concentrations were significantly lower than those in 1994 only in 2010. There were few changes in P forms determined by P-NMR. Orthophosphate followed the same trend observed for the soil P pools; total organic P, total inositol phosphates, and total orthophosphate monoesters and diesters were highest in 2010 in the soil receiving no P fertilizer for 10 yr. For these soils, fertilizer application and cessation influenced inorganic P more than organic P.

The importance of catchment vegetation for alkalinity, phosphorus burial and macrophytes as revealed by a recent paleolimnological study in a soft water lake

The land use within a catchment may markedly affect the environmental conditions in a lake and the storage capability of its sediments. This study investigated how changes in the dominant catchment vegetation (from local stands of deciduous trees over extensive heathland with some agriculture to mainly coniferous forest) occurring during the last ca. 200years were reflected in the sediments of a soft water lake and how these changes influenced the lake ecosystem. Pollen, macrofossils, metals, different phosphorus (P) forms, organic matter, carbon and nitrogen contents were determined in short sediment cores. This novel combination of proxies revealed that 1) the reduction of deciduous trees in the watershed seemingly reduced the calcium (Ca) supply to the lake and thereby its buffering capacity. This development was accompanied by decreased abundances of Ca-dependent species and subsequent increases in acidophilic species. 2) The sedimentary contents of organic matter, non-reactive P and humic-bound P were evidently higher in sediments deposited during the time when deciduous trees were abundant, which is probably linked to a stabilising effect by Ca. 3) An erosion event clearly reduced the amounts of macrofossils of isoetid species and characeans, indicating a reduction in their maximum distribution depth because of lower water transparency. Overall, the results of our paleolimnological study are of importance within lake management by convincingly showing how land use changes may (irreversibly) affect environmental conditions and species composition in soft water lakes and the storage of organic matter and P in their sediments.

Imaging Organophosphate and Pyrophosphate Sequestration on Brucite by in Situ Atomic Force Microscopy

In order to evaluate the organic phosphorus (OP) and pyrophosphate (PyroP) cycle and their fate in the environment, it is critical to understand the effects of mineral interfaces on the reactivity of adsorption and precipitation of OP and PyroP. Here, in situ atomic force microscopy (AFM) is used to directly observe the kinetics of coupled dissolution-precipitation on cleaved (001) surfaces of brucite [Mg(OH)₂] in the presence of phytate, glucose-6-phosphate (G6P) and pyrophosphate, respectively. AFM results show that the relative order of contribution to mineral surface adsorption and precipitation is phytate > pyrophosphate > G6P under the same solution conditions and can be quantified by the induction time of OP/PyroP-Mg nucleation in a boundary layer at the brucite-water interface. Calculations of solution speciation during brucite dissolution in the presence of phytate or pyrophosphate at acidic pH conditions show that the solutions may reach supersaturation with respect to Mg₅H₂Phytate.6H₂O as a Mg-phytate phase or Mg₂P₂O₇ as a Mg-pyrophosphate phase that becomes thermodynamically stable before equilibrium with brucite is reached. This is consistent with AFM dynamic observations for the new phase formations on brucite. Direct nanoscale observations of the transformation of adsorption/complexation-surface precipitation, combined with spectroscopic characterizations and species simulations may improve the mechanistic understanding of organophosphate and pyrophosphate sequestration by mineral replacement reactions through a mechanism of coupled dissolution-precipitation occurring at mineral-solution interfaces in the environment.

A short history of inositol lipids

The diverse family of inositol lipids is now known to be central to many aspects of cell biology. The route from the first discovery of inositol to our present day knowledge of inositol lipids spans more than 150 years and is long and complex. This is a brief account of some of the most important stages along that route.

The C:N:P:S stoichiometry of soil organic matter

The formation and turnover of soil organic matter (SOM) includes the biogeochemical processing of the macronutrient elements nitrogen (N), phosphorus (P) and sulphur (S), which alters their stoichiometric relationships to carbon (C) and to each other. We sought patterns among soil organic C, N, P and S in data for c. 2000 globally distributed soil samples, covering all soil horizons. For non-peat soils, strong negative correlations (p < 0.001) were found between N:C, P:C and S:C ratios and % organic carbon (OC), showing that SOM of soils with low OC concentrations (high in mineral matter) is rich in N, P and S. The results can be described approximately with a simple mixing model in which nutrient-poor SOM (NPSOM) has N:C, P:C and S:C ratios of 0.039, 0.0011 and 0.0054, while nutrient-rich SOM (NRSOM) has corresponding ratios of 0.12, 0.016 and 0.016, so that P is especially enriched in NRSOM compared to NPSOM. The trends hold across a range of ecosystems, for topsoils, including O horizons, and subsoils, and across different soil classes. The major exception is that tropical soils tend to have low P:C ratios especially at low N:C. We suggest that NRSOM comprises compounds selected by their strong adsorption to mineral matter. The stoichiometric patterns established here offer a new quantitative framework for SOM classification and characterisation, and provide important constraints to dynamic soil and ecosystem models of carbon turnover and nutrient dynamics.

Enhanced Dissolution and Transformation of ZnO Nanoparticles: The Role of Inositol Hexakisphosphate

The toxicity, reactivity, and behavior of zinc oxide (ZnO) nanoparticles (NPs) released in the environment are highly dependent on environmental conditions. Myo-inositol hexakisphosphate (IHP), a common organic phosphate, may interact with NPs and generate new transformation products. In this study, the role of IHP in mediating the dissolution and transformation of ZnO NPs was investigated in the laboratory kinetic experiments using powder X-ray diffraction, attenuated total reflectance Fourier transform infrared spectroscopy, (31)P nuclear magnetic resonance spectroscopy, high-resolution transmission electronic microscopy, and synchrotron-based extended X-ray absorption fine structure spectroscopy. The results indicate that IHP shows a dissolution-precipitation effect, which is different from citrate and EDTA that only enhances Zn dissolution. The enhanced dissolution and transformation of ZnO NPs by IHP (<0.5 h) is found to be strikingly faster than that induced by inorganic phosphate (Pi, > 3.0 h) at pH 7.0, and the reaction rate increases with decreasing pH and increasing IHP concentration. Multitechnique analyses reveal that interaction of ZnO NPs with IHP induces rapid transformation of ZnO NPs into zinc phytate complexes initially and poorly crystalline zinc phytate-like (Zn-IHP) phase finally. Additionally, ZnO NPs preferentially react with IHP and transform to Zn-IHP when Pi and IHP concurrently coexist in a system. Overall, results from this study contribute to an improved understanding of the role of organic phosphates (e.g., IHP) in the speciation and structural transformation of ZnO NPs, which can be leveraged for remediation of ZnO-polluted water and soils.

Characterization of phosphorus forms in lake macrophytes and algae by solution (31)P nuclear magnetic resonance spectroscopy

Debris from aquatic macrophytes and algae are important recycling sources of phosphorus (P), which can result in continuing blooms of algae by recycling bioavailable P in the eutrophic lakes. However, knowledge of forms of P in aquatic macrophytes and algae and their contribution to internal loads of P in lakes is limited. Without such knowledge, it is difficult to develop appropriate strategies to remediate and or restore aquatic ecosystems that have become eutrophic. Therefore, in this work, P was extracted from six types of aquatic macrophytes and algae collected from Tai Lake of China and characterized by use of solution (31)P-nuclear magnetic resonance (NMR) spectroscopy. When extracted by 0.5 M NaOH-25 mM EDTA, extraction recovery of total P(TP) and organic P(Po) exceeded 90 %. Concentrations of Po in algae and aquatic macrophytes were 5552 mg kg(-1) and 1005 mg kg(-1) and accounted for 56.0 and 47.2 % of TP, respectively. When Po, including condensed P, was characterized by solution (31)P-NMR Po in algae included orthophosphate monoesters (79.8 %), pyrophosphate (18.2 %), and orthophosphate diester (2.0 %), and Po in aquatic macrophytes included orthophosphate monoesters (90.3 %), pyrophosphate (4.2 %), and orthophosphate diester (5.5 %). Additionally, orthophosphate monoesters in algal debris mainly included β-glycerophosphate (44.1 %), α-glycerophosphate (13.5 %), and glucose 6-phosphate (13.5 %). Orthophosphate monoesters in aquatic macrophytes mainly included β-glycerophosphate (27.9 %), α-glycerophosphate (24.6 %), and adenosine 5' monophosphate (8.2 %). Results derived from this study will be useful in better understanding nutrient cycling, relevant eutrophication processes, and pollution control for freshwater lakes.

Surface speciation of myo-inositol hexakisphosphate adsorbed on TiO2 nanoparticles and its impact on their colloidal stability in aqueous suspension: A comparative study with orthophosphate

Despite extensive research demonstrating the influence of organic matter and inorganic phosphate on the stability of TiO2 nanoparticles (NPs), far less research has assessed the impact of myo-inositol hexakisphosphate (IHP), a common organic phosphate widely present in the environment. In this study, the adsorption of IHP on TiO2 NPs and its impact on their colloidal stability were investigated using batch experiments, dynamic light scattering (DLS) techniques, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) and solid-state (31)P nuclear magnetic resonance (NMR) spectroscopy. Inorganic orthophosphate (Pi) adsorption was run for comparison. The ratio of the Pi/IHP adsorption density (1.528: 0.453) at pH5.0 suggested that IHP may complex on the TiO2 surface through three of its six phosphate groups. Zeta potential measurements, ATR-FTIR and NMR spectra indicated that IHP/Pi adsorbed onto TiO2 NPs by forming inner-sphere complexes and modified the surface charge of these NPs, which exerted a great impact on their colloidal stability. Interactions between NPs measured by sedimentation and aggregation size highly depended on the pH, surface phosphorus coverage, and surface phosphorus species. The impact of IHP on the aggregation and dispersion of TiO2 NPs was significantly larger than that of Pi, in agreement with the calculation from the DLVO theory. This study highlighted the impact of IHP relative to Pi on the colloidal stability of TiO2 NPs in phosphorus-enriched environments.

The "Other" Inositols and Their Phosphates: Synthesis, Biology, and Medicine (with Recent Advances in myo-Inositol Chemistry)

Cell signaling via inositol phosphates, in particular via the second messenger myo-inositol 1,4,5-trisphosphate, and phosphoinositides comprises a huge field of biology. Of the nine 1,2,3,4,5,6-cyclohexanehexol isomers, myo-inositol is pre-eminent, with "other" inositols (cis-, epi-, allo-, muco-, neo-, L-chiro-, D-chiro-, and scyllo-) and derivatives rarer or thought not to exist in nature. However, neo- and d-chiro-inositol hexakisphosphates were recently revealed in both terrestrial and aquatic ecosystems, thus highlighting the paucity of knowledge of the origins and potential biological functions of such stereoisomers, a prevalent group of environmental organic phosphates, and their parent inositols. Some "other" inositols are medically relevant, for example, scyllo-inositol (neurodegenerative diseases) and d-chiro-inositol (diabetes). It is timely to consider exploration of the roles and applications of the "other" isomers and their derivatives, likely by exploiting techniques now well developed for the myo series.

Complex Forms of Soil Organic Phosphorus-A Major Component of Soil Phosphorus

Phosphorus (P) is an essential element for life, an innate constituent of soil organic matter, and a major anthropogenic input to terrestrial ecosystems. The supply of P to living organisms is strongly dependent on the dynamics of soil organic P. However, fluxes of P through soil organic matter remain unclear because only a minority (typically <30%) of soil organic P has been identified as recognizable biomolecules of low molecular weight (e.g., inositol hexakisphosphates). Here, we use (31)P nuclear magnetic resonance spectroscopy to determine the speciation of organic P in soil extracts fractionated into two molecular weight ranges. Speciation of organic P in the high molecular weight fraction (>10 kDa) was markedly different to that of the low molecular weight fraction (<10 kDa). The former was dominated by a broad peak, which is consistent with P bound by phosphomonoester linkages of supra-/macro-molecular structures, whereas the latter contained all of the sharp peaks that were present in unfractionated extracts, along with some broad signal. Overall, phosphomonoesters in supra-/macro-molecular structures were found to account for the majority (61% to 73%) of soil organic P across the five diverse soils. These soil phosphomonoesters will need to be integrated within current models of the inorganic-organic P cycle of soil-plant terrestrial ecosystems.

Quantitative analysis of ³¹P NMR spectra of soil extracts--dealing with overlap of broad and sharp signals

Solution (31)P NMR analysis following extraction with a mixture of sodium hydroxide and ethylenediaminetetraacetic acid is the most widely used method for detailed characterization of soil organic P. However, quantitative analysis of the (31)P NMR spectra is complicated by severe spectral overlap in the monoester region. Various deconvolution procedures have been developed for the task, yet none of these are widely accepted or implemented. In this mini-review, we first describe and compare these varying approaches. We then review approaches to similar issues of spectral overlap in biomedical science applications including NMR-based metabolic profiling and analyzing (31)P magnetic resonance spectra of ex vivo and in vivo intact tissues. The greater maturity and resourcing of this biomedical research means that a wider variety of approaches has been developed. Of particular relevance are approaches to dealing with overlap of broad and sharp signals. Although the existence of this problem is still debated in the context of soil analyses, not only is it well-recognized in biomedical applications, but multiple approaches have been developed to deal with it, including T2 editing and time-domain fitting. Perhaps the most transferable concept is the incorporation of 'prior knowledge' in the fitting of spectra. This is well established in biomedical applications but barely touched in soil analyses. We argue that shortcuts to dealing with overlap in the monoester region (31)P NMR soil spectra are likely to be found in the biomedical literature, although some degree of adaptation will be necessary.

Phytate (Inositol Hexakisphosphate) in Soil and Phosphate Acquisition from Inositol Phosphates by Higher Plants. A Review

Phosphate (P) fixation to the soil solid phase is considered to be important for P availability and is often attributed to the strong binding of orthophosphate anion species. However, the fixation and subsequent immobilization of inositolhexa and pentaphosphate isomers (phytate) in soil is often much stronger than that of the orthosphate anion species. The result is that phytate is a main organic P form in soil and the dominating form of identifiable organic P. The reasons for the accumulation are not fully clear. Two hypothesis can be found in the literature in the last 20 years, the low activity of phytase (phosphatases) in soil, which makes phytate P unavailable to the plant roots, and, on the other hand, the strong binding of phytate to the soil solid phase with its consequent stabilization and accumulation in soil. The hypothesis that low phytase activity is responsible for phytate accumulation led to the development of genetically modified plant genotypes with a higher expression of phytase activity at the root surface and research on the effect of a higher phytate activity on P acquisition. Obviously, this hypothesis has a basic assumption, that the phytate mobility in soil is not the limiting step for P acquisition of higher plants from soil phytate. This assumption is, however, not justified considering the results on the sorption, immobilization and fixation of phytate to the soil solid phase reported in the last two decades. Phytate is strongly bound, and the P sorption maximum and probably the sorption strength of phytate P to the soil solid phase is much higher, compared to that of orthophosphate P. Mobilization of phytate seems to be a promising step to make it available to the plant roots. The excretion of organic acid anions, citrate and to a lesser extend oxalate, seems to be an important way to make phytate P available to the plants. Phytase activity at the root surface seems not be the limiting step in P acquisition from phytate. Phytate is not only bound to inorganic surfaces in soil but can also be bound, similar to orthophosphate, to humic surfaces via Fe or Al bridges. Humic-metal-phytate complexes may be transported in the soil solution to the roots where hydrolysis and uptake of the liberated P may occur. Research on this topic is strongly required.

Characterization of Organic Phosphorus Form and Bioavailability in Lake Sediments using P Nuclear Magnetic Resonance and Enzymatic Hydrolysis

Lake sediments are known to be a significant source of phosphorus (P) to plankton populations under certain biogeochemical conditions; however, the contribution of sediment organic P (P) to internal P loads remains poorly understood. We investigated P speciation and bioavailability in sediments collected over multiple months from a shallow, eutrophic bay in Lake Champlain (Missisquoi Bay, VT) using solution P nuclear magnetic resonance (NMR) spectroscopy and enzymatic hydrolysis (EH) analysis of sediments collected during years with (2008) and without (2007) algal blooms. Sediments collected during bloom onset (July) and peak bloom (August) months contained the largest proportion of enzyme-labile P, whereas pre- and postbloom sediments were primarily composed of nonlabile P. Monoester P to diester P ratios changed with respect to depth, particularly during bloom periods. Monoester P and DNA accumulation, likely from settling particulate matter, began at the onset of the bloom and continued into October 2008 during the postbloom period. The disappearance of inositol hexakisphosphate stereoisomers and the generation of orthophosphate at lower sediment depths was also evident in August 2008. Principal components analysis of EH and NMR species proportions confirmed differences between sediment cores collected during bloom onset and peak bloom, compared with pre- and postbloom sediments. Large enzyme-labile and P species proportions corresponded to increased sediment P flux and reduced manganese and iron species in porewater. These findings suggest that interseasonal changes in P speciation may influence P mobility in sediments and contribute to important feedback dynamics between biological productivity and sediment water interface geochemistry.

Speciation of inositol phosphates in lake sediments by ion-exchange chromatography coupled with mass spectrometry, inductively coupled plasma atomic emission spectroscopy, and 31P NMR spectroscopy

A method for the detection and speciation of inositol phosphates (InsP(n)) in sediment samples was tested, utilizing oxalate-oxalic acid extraction followed by determination by high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) using electrospray ionization (ESI) in negative mode. The chromatographic separation was carried out using water and ammonium bicarbonate as mobile phase in gradient mode. Data acquisition under MS/MS was attained by multiple reaction monitoring. The technique provided a sensitive and selective detection of InsP(n) in sediment samples. Several forms of InsP(n) in the oxalate-oxalic acid extracted sediment were identified. InsP6 was the dominating form constituting 0.250 mg P/g DW (dry weight); InsP5 and InsP4 constituted 0.045 and 0.014 mg P/g DW, respectively. The detection limit of the LC-ESI-MS/MS method was 0.03 μM InsP(n), which is superior to the currently used method for the identification of InsP(n), (31)P nuclear magnetic resonance spectroscopy ((31)P NMR). Additionally sample handling time was significantly reduced.

Investigation of soil legacy phosphorus transformation in long-term agricultural fields using sequential fractionation, P K-edge XANES and solution P NMR spectroscopy

Understanding legacy phosphorus (P) build-up and draw-down from long-term fertilization is essential for effective P management. Using replicated plots from Saskatchewan, Canada, with P fertilization from 1967 to 1995 followed by either P fertilization or P cessation (1995-2010), soil P was characterized in surface and subsurface layers using sequential fractionation, P K-edge X-ray absorption near-edge structure (XANES) and solution (31)P nuclear magnetic resonance (P NMR) spectroscopy. Legacy P from a 28-year build-up was sufficient for 15 years of wheat cultivation, resulting in no significant differences in crop yield in 2010. In surface soils, soil test (Olsen) P decreased significantly in unfertilized plots compared with 1995, which was reflected in declining aluminum (hydr)oxide-associated inorganic P by fractionation and XANES. Furthermore, XANES analysis revealed a decrease of calcium-associated P in 2010-unfertilized soils at both depths and an increase of Fe (hydr)oxides-associated P in the 2010-fertilized and -unfertilized surface soils relative to the 1995 soils. Increased total organic P and orthophosphate diesters by P NMR and accumulated inositol hexaphosphate by XANES were observed in surface soils with P fertilization cessation. In subsurface soils, few legacy P transformations were detected. These results provide important information about legacy P to improve agricultural sustainability while mitigating water quality deterioration.