Phosphorus-31 Nuclear Magnetic Resonance Spectroscopy Research Articles

Biogeochemical cycling of soil phosphorus during natural revegetation of Pinus sylvestris on disused sand quarries in Northwestern Russia

Quarrying causes severe degradation of soils and vegetation that can be recovered partially when the quarries are abandoned and re-colonised by plants. To understand the recovery of soil functionality and nutrient cycling, we studied the development of soil phosphorus pools during Scots pine (Pinus sylvestris) revegetation in a disused sand quarry in Northwestern Russia. Sites that had been developing for different times since abandonment were compared to the parent sand and an adjacent undisturbed forest. Phosphorus speciation in genetic horizons of soil profiles was determined by sequential fractionation and solution phosphorus-31 nuclear magnetic resonance spectroscopy. Rapid transformations in soil properties occurred in 40 years, with a marked decline in pH and an accumulation of organic matter. Phosphorus transformations were shaped by geochemical processes, with a rapid release of inorganic phosphorus from primary minerals and accumulation of organic phosphorus to concentrations exceeding those found in the undisturbed site. Adsorbed and/or precipitated phosphorus increased rapidly, despite few reactive mineral colloidal surfaces. Natural succession of Scots pine in post-mining landscapes promotes ecosystem restoration through the rapid re-establishment of the biogeochemical cycles of organic matter and phosphorus. This study provides an important example of biogeochemical phosphorus cycling during the initial stages of pedogenesis.

Organic phosphorus fractionation in wetland soil profiles by chemical extraction and phosphorus-31 nuclear magnetic resonance spectroscopy

Organic P (OP) plays an important role in soil P cycling and is a potential P source for wetland plants. In this study, a modified chemical sequential fractionation method and 31P nuclear magnetic resonance spectroscopy (31P NMR) of NaOH–EDTA extracts were used to examine the distribution of organic P fractions and compounds in soil profiles of the Beijing Yeyahu Wetland, China. The influence of acid treatment prior to NaOH–EDTA extraction on 31P NMR spectra was also investigated. Results show that highly resistant OP was the major class of organic P. The rank order of organic P fractions was highly resistant OP (on average accounting for 68.5% of total OP)>moderately resistant OP (15.8%m of total OP)>moderately labile OP (11.4% of total OP)>labile OP (4.3% of total OP). Most of the organic P fractions decreased with soil depth due to the accumulation of plant residues in surface soils and the deposition and diagenesis of soils. Moderately (r=0.586, p<0.01) and highly (r=0.741, p<0.01) resistant OP fractions were positively correlated with soil organic matter. Phosphorus compounds including orthophosphate (23–74.6% of total P in spectra), monoester phosphate (18.6–76%), diester phosphate (nil-7.8%) and pyrophosphate (nil-6.7%) were characterized using 31P NMR. Monoester-P was the dominant soil organic P compound identified. The proportion of monoester-P increased significantly in NaOH–EDTA extracts with HCl pretreatment and it was confirmed by chemical analysis. Therefore, it can be concluded that HCl pretreatment can remove more than half of the inorganic P and increase the overall recovery rate of organic P during subsequent NaOH–EDTA extraction, which might be a new approach for organic P detection. Furthermore, the OP chemical sequential fractionation method presented in this study is an integrated and comprehensive approach which can be used for further verification.

Administration of exogenous adenosine triphosphate to ischemic skeletal muscle induces an energy-sparing effect: Role of adenosine receptors

BackgroundIschemia–reperfusion injury is a devastating complication that occurs in allotransplantation and replantation of limbs. Over the years, several preservation strategies have been used to conserve the critical levels of intracellular adenosine triphosphate (ATP) during ischemia to sustain the ion gradients across the membranes and thus the tissue viability. The administration of exogenous ATP to ischemic tissues is known to provide beneficial effects during reperfusion, but it is unclear whether it provides protection during ischemia. The purpose of the present study was to determine the effect of ATP administration on high-energy phosphate levels in ischemic skeletal muscle and to examine the role of purinergic and adenosine receptors in mediating the response to exogenous ATP. MethodsThe extensor digitorum longus muscles of Fischer rats were subjected to ischemia and treated with different concentrations of ATP with or without purinergic and adenosine receptor blockers. Phosphorus-31 nuclear magnetic resonance spectroscopy was used to measure the rate of decay of ATP, phosphocreatine (PCr), and the formation of adenosine monophosphate and acidification. Phosphorylated compounds were analyzed using a simple model of energy metabolism, and the PCr half-life was used as an index of internal depletion of ATP to distinguish between intracellular and extracellular ATP. ResultsPCr decay was rapid in all muscle groups and was followed by gradual ATP decay. The half-life of PCr was significantly longer in the ATP-treated muscles than in the vehicle controls and was maximally prolonged by treating with slow hydrolyzing adenosine 5′-O-(3-thio)triphosphate. Purinoceptor (P2X) blockade with ATP treatment significantly increased the half-life of PCr, and adenosine receptor blockers blunted the response. Administration of adenosine to ischemic muscles significantly increased the half-life of PCr compared with that in the vehicle controls. ConclusionsExogenous ATP administration to ischemic skeletal muscles appears to spare intracellular energy by acting primarily through adenosine receptors.

Synthesis, characterization and molecular structure of Ru(II) complex with benzoylpyrazine carboxylic acid derivatives

Two benzoylpyrazine ligands containing carboxyl and amide functions and their hydride-carbonyl complexes of ruthenium were synthesized and characterized by infrared, proton, carbon phosphorus nuclear magnetic resonance, electronic absorption and emission spectroscopy and X-ray crystallography. The experimental studies were completed by theoretical calculations. From the electronic spectrum of the complex the Racah’s and nepheloauxetic parameters are calculated. The electronic structure of the complexes, presented in particular by the density of states diagram, have been correlated with its ability to fluoresce and used to analyze the UV–Vis spectra.

POLI-Mix Functional Food Enhances Steady-State Bioenergetic Status Independently of Age: An Experimental Study

BALB/c mice were divided into young, middle-aged, and aged groups, and each group was given 3 weeks of oral treatments: (1) 1 mL of VBC1-99 (a mixture of 42 fruits and vegetables extracts) or (2) 1 mL of same amount of antioxidant vitamins as control. Steady-state hepatic adenosine triphosphate (ATP) was assessed by phosphorus-31 nuclear magnetic resonance ((31)P-NMR) spectroscopy as: β-ATP/reference peak, inorganic phosphorus (Pi)/peak and β-ATP/Pi. As compared to untreated control, VBC1-99 significantly enhanced β-ATP/peak and β-ATP/Pi ratios (p<0.01) in all age groups and throughout the observation period (p<0.05) together with a significant decrease of Pi/ref peak ratio (p<0.05). However, this value in middle-aged and aged mice was comparable to antioxidant control mice. These NMR data demonstrate that VBC1-99 has a beneficial effect on hepatic energy metabolism, irrespective of age.

Analytical techniques tailored for biomass transformation to biofuels

An analytical platform was developed for the detection of biomass oxygenates and biocarbon in biogasoline produced by coprocessing of hydrodeoxygenated pyrolysis oils (HDO‐oil) and vacuum gas oil. A combination of different analytical techniques is necessary for analyzing such complex mixtures. The presence of various oxygenated compounds such as alcohols, acids, and phenols was quantified using phosphorus nuclear magnetic resonance spectroscopy. Different alkylphenols were identified using two‐dimensional gas chromatography‐mass spectrometry. The transformations of lignin oligomers present in HDO‐oil were determined with size‐exclusion chromatography carried out for the products. Accelerator mass spectrometry was used to make the distinction between carbonaceous material of biological origin and that of fossil origin. This type of analytical platform, which is tailored for bio‐oil identification and quantification, appears to be required for exploratory catalyst research and kinetic studies in this rapidly expanding domain. © 2011 American Institute of Chemical Engineers Environ Prog, 32: 377‐383, 2013

Synthesis, characterization and molecular structure of Ru(II) complex with 8-hydroxyquinoline derivative

The new ( E)-8-hydroxyquinoline-2-carbaldehyde O-benzyl oxime ligand and its hydride–carbonyl complex of ruthenium was synthesized and characterized by infrared, proton and phosphorus nuclear magnetic resonance, electronic absorption and emission spectroscopy and X-ray crystallography. The experimental studies were complemented by theoretical calculations. From the electronic spectrum of the complex the Racah’s and nepheloauxetic parameters are calculated. The electronic structure of the complexes, presented in particular by the density of states diagram, have been correlated with its ability to fluoresce and used to analyze the UV–Vis spectra.

Phosphorus-31 and vanadium-51 solid-state nuclear magnetic resonance spectroscopy of β-vanadyl phosphate — Effects of homo- and heteronuclear spin-spin, electrostatic, and paramagnetic interactions

Field-dependent 31P solid-state NMR studies demonstrate that the line shape in spectra of β-VOPO4 depends on 51V–31P direct and indirect spin-spin interactions (M2 (51V, 31P) = 101(23) × 106 rad2 s–2, 2Jiso (51V, 31P) = 48(5) Hz) and, to a lesser extent, on 31P chemical shift anisotropy (δiso = –10.4(2), Ω = δ11 – δ33 = 22(2) ppm) and 31P–31P interactions (M2 (31P, 31P) = 6.7(1) × 106 rad2 s–2). In contrast, homonuclear dipolar interactions play an important role for the field and spinning rate dependent 31P spin-lattice relaxation via paramagnetic impurities (T1 = 20–60 s). Vanadium-51 magic-angle spinning NMR spectra indicate a sizeable chemical shift anisotropy (δiso = –754(1), δ11 = –336(10), δ22 = –344(6), δ33 = –1581(8) ppm) and nuclear quadrupole interaction (χ = 1.5(1) MHz, η = 0.35(5)); the principal axis systems of both interactions are clearly not coincident, with an angle of 35(5)° between the greatest component of the electric field gradient tensor and δ33.

Lipidomic changes in rat liver after long-term exposure to ethanol

Alcoholic liver disease (ALD) is a serious health problem with significant morbidity and mortality. In this study we examined the progression of ALD along with lipidomic changes in rats fed ethanol for 2 and 3months to understand the mechanism, and identify possible biomarkers. Male Fischer 344 rats were fed 5% ethanol or caloric equivalent of maltose–dextrin in a Lieber-DeCarli diet. Animals were killed at the end of 2 and 3months and plasma and livers were collected. Portions of the liver were fixed for histological and immunohistological studies. Plasma and the liver lipids were extracted and analyzed by nuclear magnetic resonance (NMR) spectroscopy. A time dependent fatty infiltration was observed in the livers of ethanol-fed rats. Mild inflammation and oxidative stress were observed in some ethanol-fed rats at 3months. The multivariate and principal component analysis of proton and phosphorus NMR spectroscopy data of extracted lipids from the plasma and livers showed segregation of ethanol-fed groups from the pair-fed controls. Significant hepatic lipids that were increased by ethanol exposure included fatty acids and triglycerides, whereas phosphatidylcholine (PC) decreased. However, both free fatty acids and PC decreased in the plasma. In liver lipids unsaturation of fatty acyl chains increased, contrary to plasma, where it decreased. Our studies confirm that over-accumulation of lipids in ethanol-induced liver steatosis accompanied by mild inflammation on long duration of ethanol exposure. Identified metabolic profile using NMR lipidomics could be further explored to establish biomarker signatures representing the etiopathogenesis, progression and/or severity of ALD.

High-Throughput Measurement and Classification of Organic P in Environmental Samples

Many types of organic phosphorus (P) molecules exist in environmental samples1. Traditional P measurements do not detect these organic P compounds since they do not react with colorimetric reagents2,3. Enzymatic hydrolysis (EH) is an emerging method for accurately characterizing organic P forms in environmental samples4,5. This method is only trumped in accuracy by Phosphorus-31 Nuclear Magnetic Resonance Spectroscopy (31P-NMR) -a method that is expensive and requires specialized technical training6. We have adapted an enzymatic hydrolysis method capable of measuring three classes of phosphorus (monoester P, diester P and inorganic P) to a microplate reader system7. This method provides researchers with a fast, accurate, affordable and user-friendly means to measure P species in soils, sediments, manures and, if concentrated, aquatic samples. This is the only high-throughput method for measuring the forms and enzyme-lability of organic P that can be performed in a standard laboratory. The resulting data provides insight to scientists studying system nutrient content and eutrophication potential.

High-Throughput Measurement and Classification of Organic P in Environmental Samples

Many types of organic phosphorus (P) molecules exist in environmental samples1. Traditional P measurements do not detect these organic P compounds since they do not react with colorimetric reagents2,3. Enzymatic hydrolysis (EH) is an emerging method for accurately characterizing organic P forms in environmental samples4,5. This method is only trumped in accuracy by Phosphorus-31 Nuclear Magnetic Resonance Spectroscopy (31P-NMR) -a method that is expensive and requires specialized technical training6. We have adapted an enzymatic hydrolysis method capable of measuring three classes of phosphorus (monoester P, diester P and inorganic P) to a microplate reader system7. This method provides researchers with a fast, accurate, affordable and user-friendly means to measure P species in soils, sediments, manures and, if concentrated, aquatic samples. This is the only high-throughput method for measuring the forms and enzyme-lability of organic P that can be performed in a standard laboratory. The resulting data provides insight to scientists studying system nutrient content and eutrophication potential.

The inositol phosphates in soils and manures: Abundance, cycling, and measurement

Giles, C. D., Cade-Menun, B. J. and Hill, J. E. 2011. The inositol phosphates in soils and manures: Abundance, cycling, and measurement. Can. J. Soil Sci. 91: 397-416. This review focuses on recent advances in understanding the origins, abiotic and biotic cycling, and measurement of inositol phosphates (IPx) in manures and soils. With up to eight orthophosphates bound to inositol via ester linkages, this class of compounds has the potential to be unavailable to enzymatic hydrolysis when sorbed or in complex with soil metals, limiting the release of phosphorus (P) for uptake by plants. However, hydrolysis of IPx by microbial phytases in aquatic environments could result in a potent source of the eutrophication agent orthophosphate. This review discusses the forms and stereoisomers of IPx that have been identified in environmental samples. Next, it discusses the various techniques used to identify IPx, including extraction and concentration, separation techniques such as electrophoresis, spectroscopic methods such as phosphorus-31 nuclear magnetic resonance spectroscopy (31P-NMR), mass spectrometry and X-ray absorption near-edge structure (XANES), and enzymatic techniques, such as enzyme hydrolysis (EH). Recent advances in knowledge about abiotic and biotic factors controlling the cycling of IPx in soil, manure and water are summarised, including soil characteristics affecting IPx sorption, transportation processes, and the microbial production and degradation of IPx. Finally, areas for future research focus are discussed.

The inositol phosphates in soils and manures: Abundance, cycling, and measurement

Giles, C. D., Cade-Menun, B. J. and Hill, J. E. 2011. The inositol phosphates in soils and manures: Abundance, cycling, and measurement. Can. J. Soil Sci. 91: 397–416. This review focuses on recent advances in understanding the origins, abiotic and biotic cycling, and measurement of inositol phosphates (IPx) in manures and soils. With up to eight orthophosphates bound to inositol via ester linkages, this class of compounds has the potential to be unavailable to enzymatic hydrolysis when sorbed or in complex with soil metals, limiting the release of phosphorus (P) for uptake by plants. However, hydrolysis of IPx by microbial phytases in aquatic environments could result in a potent source of the eutrophication agent orthophosphate. This review discusses the forms and stereoisomers of IPx that have been identified in environmental samples. Next, it discusses the various techniques used to identify IPx, including extraction and concentration, separation techniques such as electrophoresis, spectroscopic methods such as phosphorus-31 nuclear magnetic resonance spectroscopy (31P-NMR), mass spectrometry and X-ray absorption near-edge structure (XANES), and enzymatic techniques, such as enzyme hydrolysis (EH). Recent advances in knowledge about abiotic and biotic factors controlling the cycling of IPx in soil, manure and water are summarised, including soil characteristics affecting IPx sorption, transportation processes, and the microbial production and degradation of IPx. Finally, areas for future research focus are discussed.

Phosphorus Forms and Chemistry in the Soil Profile under Long‐Term Conservation Tillage: A Phosphorus‐31 Nuclear Magnetic Resonance Study

In many regions, conservation tillage has replaced conventional tilling practices to reduce soil erosion, improve water conservation, and increase soil organic matter. However, tillage can have marked effects on soil properties, specifically nutrient redistribution or stratification in the soil profile. The objective of this research was to examine soil phosphorus (P) forms and concentrations in a long-term study comparing conservation tillage (direct drilling, "No Till") and conventional tillage (moldboard plowing to 20 cm depth, "Till") established on a fine sandy loam (Orthic Humo-Ferric Podzol) in Prince Edward Island, Canada. No significant differences in total carbon (C), total nitrogen (N), total P, or total organic P concentrations were detected between the tillage systems at any depth in the 0- to 60-cm depth range analyzed. However, analysis with phosphorus-31 nuclear magnetic resonance spectroscopy showed differences in P forms in the plow layer. In particular, the concentration of orthophosphate was significantly higher under No Till than Till at 5 to 10 cm, but the reverse was true at 10 to 20 cm. Mehlich 3-extractable P was also significantly higher in No Till at 5 to 10 cm and significantly higher in Till at 20 to 30 cm. This P stratification appears to be caused by a lack of mixing of applied fertilizer in No Till because the same trends were observed for pH and Mehlich 3-extractable Ca (significantly higher in the Till treatment at 20 to 30 cm), reflecting mixing of applied lime. The P saturation ratio was significantly higher under No Till at 0 to 5 cm and exceeded the recommended limits, suggesting that P stratification under No Till had increased the potential for P loss in runoff from these sites.

Identification of organic phosphorus compounds in the Bronx River bed sediments by phosphorus-31 nuclear magnetic resonance spectroscopy

Sediment characteristics influence the distribution and bioavailability of phosphorus (P) in rivers and lakes. The objectives of this study were to identify P compounds in sediments collected from 15 sites along the Bronx River to get insights on nutrient transport for management of highly variable and modified ecosystems such as the Bronx River. The nuclear magnetic resonance spectra showed that the dominant P species in Bronx River bed sediments are orthophosphate monoester and lesser phosphate diesters and pyrophosphates (pyro-P). The P compounds were mostly glycerophosphate, nucleoside monophosphates, and polynucleotides. A few sites showed a small amount of dihydroxyacetone phosphate, inosine monophosphate. By allowing a downstream comparison of P compound variations along the Bronx River, this study provides a step toward improving water quality in an urban river system such as New York City and helps to assess the bioavailability of P, in turn, design estuary habitat restoration projects in comparable region of the world.

Destabilization of the emulsion formed during the enzyme-assisted aqueous extraction of oil from soybean flour

Soybean oil extraction from soybean flour by a neutral metallo-endopeptidase enzyme-assisted aqueous extraction process, optimized for effectiveness in reducing oil content of the solid residue, yields a small fraction of the oil as free oil whereas most is emulsified in a cream layer. Analysis of the cream showed the presence of peptides/proteins and phospholipids, either of which could serve as emulsifiers. Several demulsification treatments targeting these components – protease addition, phospholipase addition, and acidification (pH 4.5) – were evaluated for effectiveness against the targeted emulsifiers and in conversion of the cream to free oil. Acidification increased the oil yield from 2% to 83%. After a two-stage enzymatic demulsification process with an alkaline endopeptidase, the oil recovery increased to 95%. A lysophospholipase A 1 treatment at pH 4.5 provided complete conversion of emulsified to free oil. The phospholipids (PL) present in the original and post-treatment cream were quantified using phosphorus-31 nuclear magnetic resonance spectroscopy. PL contained phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidic acid (PA) and their lyso-derivatives. Protein size distribution, PL proportions and fatty acid composition changed after the demulsification treatments. Recycle of the endopeptidase is feasible as more than 90% of its activity was retained.

Early Beneficial Effects of Bone Marrow-Derived Mesenchymal Stem Cells Overexpressing Akt on Cardiac Metabolism After Myocardial Infarction

Administration of mesenchymal stem cells (MSCs) is an effective therapy to repair cardiac damage after myocardial infarction (MI) in experimental models. However, the mechanisms of action still need to be elucidated. Our group has recently suggested that MSCs mediate their therapeutic effects primarily via paracrine cytoprotective action. Furthermore, we have shown that MSCs overexpressing Akt1 (Akt-MSCs) exert even greater cytoprotection than unmodified MSCs. So far, little has been reported on the metabolic characteristics of infarcted hearts treated with stem cells. Here, we hypothesize that Akt-MSC administration may influence the metabolic processes involved in cardiac adaptation and repair after MI. MI was performed in rats randomized in four groups: sham group and animals treated with control MSCs, Akt-MSCs, or phosphate-buffered saline (PBS). High energy metabolism and basal 2-deoxy-glucose (2-DG) uptake were evaluated on isolated hearts using phosphorus-31 nuclear magnetic resonance spectroscopy at 72 hours and 2 weeks after MI. Treatment with Akt-MSCs spared phosphocreatine stores and significantly limited the increase in 2-DG uptake in the residual intact myocardium compared with the PBS- or the MSC-treated animals. Furthermore, Akt-MSC-treated hearts had normal pH, whereas low pH was measured in the PBS and MSC groups. Correlative analysis indicated that functional recovery after MI was inversely related to the rate of 2-DG uptake. We conclude that administration of MSCs overexpressing Akt at the time of infarction results in preservation of normal metabolism and pH in the surviving myocardium.

Detection of phosphorus species in sediments of artificial landscape lakes in China by fractionation and phosphorus-31 nuclear magnetic resonance spectroscopy

Phosphorus (P) pollution in the sediments of seven artificial landscape lakes was studied via fractionation and phosphorus-31 nuclear magnetic resonance ( 31P NMR) spectroscopy. The lake sediments accumulated significant amounts of P from supplementation with reclaimed water and from runoff from the golf course lawns. The differences in total sediment P among lakes were correlated to the varied pollution extent from the lawns. One striking feature of the artificial lake sediments was the insufficiency of NaOH-extracted Al, which plays an important role in avoiding internal P release during anoxia. Another characteristic was the dominance of orthophosphate in the NaOH–EDTA extractants of the sediments, due to the heavy external P pollution. Phytate, considered prevalent in many soils and lake sediments, as well as polyphosphates and phosphonates which have appeared in some natural lake sediments, was not detected. The rank order of present biogenic P species was monoester-P > DNA-P > pyrophosphate > lipid-P.

Analysis of Monoglycerides, Diglycerides, Sterols, and Free Fatty Acids in Coconut (Cocos nucifera L.) Oil by 31P NMR Spectroscopy

Phosphorus-31 nuclear magnetic resonance spectroscopy ( (31)P NMR) was used to differentiate virgin coconut oil (VCO) from refined, bleached, deodorized coconut oil (RCO). Monoglycerides (MGs), diglycerides (DGs), sterols, and free fatty acids (FFAs) in VCO and RCO were converted into dioxaphospholane derivatives and analyzed by (31)P NMR. On the average, 1-MG was found to be higher in VCO (0.027%) than RCO (0.019%). 2-MG was not detected in any of the samples down to a detection limit of 0.014%. On the average, total DGs were lower in VCO (1.55%) than RCO (4.10%). When plotted in terms of the ratio [1,2-DG/total DGs] versus total DGs, VCO and RCO samples grouped separately. Total sterols were higher in VCO (0.096%) compared with RCO (0.032%), and the FFA content was 8 times higher in VCO than RCO (0.127% vs 0.015%). FFA determination by (31)P NMR and titration gave comparable results. Principal components analysis shows that the 1,2-DG, 1,3-DG, and FFAs are the most important parameters for differentiating VCO from RCO.

Soil Organic Phosphorus Transformations During Pedogenesis

Long-term changes in soil phosphorus influence ecosystem development and lead to a decline in the productivity of forests in undisturbed landscapes. Much of the soil phosphorus occurs in a series of organic compounds that differ in their availability to organisms, but changes in the relative abundance of these compounds during pedogenesis remain unknown. We used alkaline extraction and solution phosphorus-31 nuclear magnetic resonance spectroscopy to assess the chemical nature of soil organic phosphorus along a 120,000-year post-glacial chronosequence at Franz Josef, New Zealand. Inositol phosphates, DNA, phospholipids, and phosphonates accumulated rapidly during the first 500 years of soil development characterized by nitrogen limitation of biological productivity, but then declined slowly to low concentrations in older soils characterized by intense phosphorus limitation. However, the relative contribution of the various compounds to the total organic phosphorus varied along the sequence in dramatic and surprising ways. The proportion of inositol hexakisphosphate, conventionally considered to be relatively recalcitrant in the environment, declined markedly in older soils, apparently due to a corresponding decline in amorphous metal oxides, which weather to crystalline forms during pedogenesis. In contrast, the proportion of DNA, considered relatively bioavailable in soil, increased continually throughout the sequence, due apparently to incorporation within organic structures that provide protection from biological attack. The changes in soil organic phosphorus coincided with marked shifts in plant and microbial communities, suggesting that differences in the forms and bioavailability of soil organic phosphorus have ecological significance. Overall, the results strengthen our understanding of phosphorus transformations during pedogenesis and provide important insight into factors regulating the composition of soil organic phosphorus.