Solution 31P NMR Spectroscopy Research Articles

Cerium(IV) Nitrate Complexes With Bidentate Phosphine Oxides

AbstractThe reactions between ceric ammonium nitrate, (NH4)2Ce(NO3)6, (CAN) and the bidentate phosphine oxides, 4,5‐bis(diphenylphosphine oxide)‐9,9‐dimethylxanthene (L1), oxydi‐2,1‐phenylene bis(diphenylphosphine dioxide) (L2), 1,2‐bis(diphenylphosphino)ethane dioxide (L3) and 1,4‐bis(diphenylphosphino)butane dioxide, L4 have been investigated. The crystal structures of the molecular Ce(NO3)4L1 (1), and ionic [Ce(NO3)3L32][NO3]⋅CHCl3 (3), [Ce(NO3)3L32][NO3] (4) and the polymeric [Ce(NO3)3L41.5] [NO3] (5) and the cerium(III) complex [Ce(NO3)2L12][NO3] (2) are reported. The thermal stability of the complexes has been examined by thermogravimetry with the gaseous decomposition products analysed by infrared spectroscopy. Evolution of CO2 is found for both Ce(III) and Ce(IV) complexes with the later also forming NO2. The formation of the complexes in solution has been studied by 31P NMR spectroscopy and further complexes [Ce(NO3)3L12]+[NO3]− and [Ce(NO3)2L13]2+2[NO3]− identified in CD3CN solution. The complex (1) exists as a single molecular species in solution and is stable in dichloromethane whilst (3) decomposes on standing in both CD2Cl2 and CD3CN to Ce(III) containing species. Complexes of L2 have been identified by solution 31P NMR spectroscopy and these decompose in solution to give Ce(NO3)3L22. This study represents the first structural characterisations of Ce(IV) complexes with bidentate phosphine oxides.

A series of isomorphic cobalt(II), nickel(II) and zinc(II) complexes of mixed dithiophosphonate, 2,2-bipyridine and 1,10-phenanthroline ligands: Synthesis, structure, and theoretical calculations

Transition-metal complexes of dithiophosphonate ligands have attracted recent interest due to their involvement in several established and newly emerging applications. Herein, we report on the synthesis of six new complexes of Co(II), Ni(II), and Zn(II) and mixed dichalcogen (dithiophosphonate) and dipnictogen (2,2-bipyridine, and 1,10-phenanthroline) ligands: [Co{(S2P(4-C6H4OMe)(OCH(CH2CH3)2}2(C10H8N2)] 1, [Co{(S2P(4-C6H4OMe)(OCH2CH2CH2CH3)}2(C10H8N2)] 2, [Ni{S2P(4-C6H4OMe)(OCH3)}2(C12H8N2)] 3, [Ni{(S2P(4-C6H4OMe)(OCH(CH2CH3)2)}2(C12H8N2)] 4, [Zn{(S2P(4-C6H4OMe)(OCH3)}2 (C12H8N2)] 5 and [Zn{(S2P(4-C6H4OMe)(OCH2CH3)}2(C12H8N2)] 6. The complexes were characterized by solution 1H and 31P NMR spectroscopy, electrospray ionization mass spectrometry, elemental analysis, and FTIR. The crystal structures of 1, 3, 5, and 6 were established by single-crystal X-ray diffraction analysis. The four complexes are isomorphic and crystallize in the triclinic system, space group P-1, with Z = 2. Density functional theory (DFT) calculations of the electronic and structural properties of the complexes were carried out to estimate different quantum chemical properties. Crystallographic analysis showed that the Co(II) and Ni(II) metal centers in 1 and 3, respectively, adopted a distorted octahedral geometry, coordinating through the S (dithiophosphonate) and N (dipnictogen) donor atoms, while the Zn(II) center in 5 and 6 both adopted tetrahedral geometries. The obtained computational-based chemical parameters proved to be significant in evaluating the plausible reactivity and stability patterns of these complexes.

Formation of a P162- Ink from Elemental Red Phosphorus in a Thiol-Amine Mixture.

A P162- polyphosphide dianion ink was produced by the reaction of red phosphorus with a binary thiol-amine mixture of ethanethiol (ET) and ethylenediamine (en). The polyphosphide was identified by solution 31P NMR spectroscopy and electrospray ionization mass spectrometry. This solute was compared to the reaction products of white phosphorus (P4) and other elemental pnictides in the same solvent system. The reaction of P4 with ET and en gives the same P162- polyphosphide; however, the easier handling and lower reactivity of red phosphorus highlights the novelty of that reaction. Elemental arsenic and antimony both give mononuclear pnictogen-sulfide-thiolate complexes upon reaction with ET and en under otherwise identical conditions, with this difference likely resulting from the greater covalency and tendency of phosphorus to form P-P bonds.

Binding Affinity of Monoalkyl Phosphinic Acid Ligands toward Nanocrystal Surfaces

We recently introduced monoalkyl phosphinic acids as a ligand class for nanocrystal (NC) synthesis. Their metal salts have interesting reactivity differences compared to metal carboxylates and phosphonates and provide a cleaner work-up compared to phosphonates. However, little is known about the surface chemistry of NCs with monoalkyl phosphinate ligands. Here, we probe the relative binding affinity of monoalkyl phosphinate ligands with respect to other X-type ligands. We perform competitive ligand exchange reactions with carboxylate and phosphonate ligands at the surface of hafnia, cadmium selenide, and zinc sulfide NCs. We monitor the ligand shell composition by solution 1H and 31P NMR spectroscopy. Using a monoalkyl phosphinic acid with an ether functionality, we gain an additional NMR signature, apart from the typical alkene resonance in oleic acid and oleylphosphonic acid. We find that carboxylate ligands are easily exchanged upon exposure to monoalkyl phosphinic acids, whereas an equilibrium is reached between monoalkyl phosphinates and phosphonates, slightly in the favor of phosphonate (K = 2). Phosphinic acids have thus an intermediate binding affinity between carboxylic acids and phosphonic acids for all the NCs studied. These results enable the sophisticated use of monoalkyl phosphinic acids for NC synthesis and for post-synthetic surface engineering.

Adsorption mechanisms of inositol hexakisphosphate in the presence of phosphate at the amorphous aluminum oxyhydroxide-water interface.

Myo-inositol hexakisphosphate (myo-IHP) is one of the most common soil organic phosphorus (P) species in soil. Its retention in soil is often competed by phosphate, making bioavailability of P species difficult. In this study, the adsorption mechanism of myo-IHP at the amorphous aluminum (oxyhydr)oxide (AAH)-water interface was investigated at pH 6.5 in the presence of phosphate using batch adsorption experiments and solution 31P NMR spectroscopy. The ratio of [myo-IHP]i/[phosphate]i (Ri) was kept 0.33-3 while ligand addition was varied. In the absence of phosphate, myo-IHP forms inner-sphere surface complexes in AAH via P1,3, P2, P4,6, and P5 functional group coordination. When two ligands were simultaneously added, fewer P functional groups of myo-IHP coordinated to AAH and the surface complexes were altered with the coordination of mainly P1,3 and P2 functional groups. When phosphate was pre-adsorbed, myo-IHP adsorption decreased by 8.0-44% compared to the respective simultaneous addition system. P2 or P5 functional group was predominantly coordinated to the AAH surfaces at Ri = 0.33. Myo-IHP pre-adsorption resulted in an increase in the final myo-IHP adsorption compared to that in the simultaneous addition system under the respective Ri values (0.33-3). In this system, P1,3, P2, P4,6, and P5 functional groups were coordinated to form inner-sphere surface complexes regardless of Ri. The study revealed that the functional group specific adsorption mechanism of myo-IHP at the AAH-water interface was affected by addition sequence and Ri of two ligands. The competitive adsorption between organic P and phosphate plays an important role in the fate of P in soils.

Organic anions facilitate the mobilization of soil organic phosphorus and its subsequent lability to phosphatases

PurposeOrganic anions commonly released from plant roots and microorganisms are widely reported to mobilize soil phosphorus (P). We characterized soil organic P that was mobilized by organic anions and assessed its amenability to hydrolysis by phosphatase enzymes.MethodsSix soils differing in organic P concentration were extracted with citrate, malate or oxalate solutions and incubated with preparations of phosphomonoesterase, phosphodiesterase, or phytase. Organic P compounds present in these extracts were putatively identified and quantified with solution 31P-NMR spectroscopy and the enzyme-labile P fractions were assessed by changes in molybdate-reactive P (MRP) concentration.ResultsOrganic P mobilization varied markedly among the organic anions. Extraction with 10 mM citrate was most effective and extracted 7.8-fold more total P than the water controls across all soils. Approximately 95% of the extracted P was non-MRP. The organic anions increased both the amount of P extracted and the proportion of the total extracted P that was phosphatase-labile. Phytase was generally the most effective enzyme with up to 60% of the total non-MRP being amenable to hydrolysis by phytase across all extracts. The presence of inositol hexakisphosphates in the extracts, as well as other forms of organic P including nucleic acids and phospholipids, was verified by 31P-NMR with concentrations dependent on both organic anions and soil type.ConclusionThe combination of organic anions and phosphatases represents a key mechanism by which plants and microorganisms can enhance the bioavailability of soil P. This has important implications for understanding P dynamics in natural and managed ecosystems and for ongoing efforts to improve the P-acquisition efficiency of agricultural plants.

Identification of lower-order inositol phosphates (IP<sub>5</sub> and IP<sub>4</sub>) in soil extracts as determined by hypobromite oxidation and solution <sup>31</sup>P NMR spectroscopy

Abstract. Inositol phosphates (IPs) are a major pool of identifiable organic phosphorus (P) in soil. However, insight into their distribution and cycling in soil remains limited, particularly of lower-order IP (IP5 and IP4). This is because the quantification of lower-order IP typically requires a series of chemical extractions, including hypobromite oxidation to isolate IP, followed by chromatographic separation. Here, for the first time, we identify the chemical nature of organic P in four soil extracts following hypobromite oxidation using solution 31P NMR spectroscopy and transverse relaxation (T2) experiments. Soil samples analysed include A horizons from a Ferralsol (Colombia), a Cambisol and a Gleysol from Switzerland, and a Cambisol from Germany. Solution 31P nuclear magnetic resonance (NMR) spectra of the phosphomonoester region in soil extracts following hypobromite oxidation revealed an increase in the number of sharp signals (up to 70) and an on average 2-fold decrease in the concentration of the broad signal compared to the untreated soil extracts. We identified the presence of four stereoisomers of IP6, four stereoisomers of IP5, and scyllo-IP4. We also identified for the first time two isomers of myo-IP5 in soil extracts: myo-(1,2,4,5,6)-IP5 and myo-(1,3,4,5,6)-IP5. Concentrations of total IP ranged from 1.4 to 159.3 mg P per kg soil across all soils, of which between 9 % and 50 % were comprised of lower-order IP. Furthermore, we found that the T2 times, which are considered to be inversely related to the tumbling of a molecule in solution and hence its molecular size, were significantly shorter for the underlying broad signal compared to for the sharp signals (IP6) in soil extracts following hypobromite oxidation. In summary, we demonstrate the presence of a plethora of organic P compounds in soil extracts, largely attributed to IPs of various orders, and provide new insight into the chemical stability of complex forms of organic P associated with soil organic matter.

Identification of inositol phosphates (IP6, IP5 and IP4) in hypobromite oxidised soil extracts as determined by solution 31P NMR spectroscopy

Identification of inositol phosphates (IP6, IP5 and IP4) in hypobromite oxidised soil extracts as determined by solution 31P NMR spectroscopy

Extraction and quantification of polyphosphates in activated sludge from waste water treatment plants by 31P NMR spectroscopy

Polyphosphate (poly-P) is a major constituent in activated sludge from wastewater treatment plants with enhanced biological phosphorus removal due to poly-P synthesis by poly-P accumulating organisms where it plays an important role for recovery of phosphorus from waste water. Our aim was to develop a reliable protocol for poly-P quantification by 31P NMR spectroscopy. This has so far been complicated by the risks of inefficient extraction and poly-P hydrolysis in the extracts. A protocol for complete extraction, identification and quantification of poly-P in activated sludge from a waste water treatment plant was identified based on test and evaluation of existing extraction protocols in combination with poly-P determination and quantification by solution and solid state 31P NMR spectroscopy. The total poly-P middle group content was quantified by solid state NMR for comparison with the poly-P middle groups quantified by solution NMR, which is novel. Three different extraction protocols previously used in literature were compared: 1) a single 0.25 M NaOH-0.05 M EDTA extraction, 2) a 0.05 M EDTA pre-extraction followed by a 0.25 M NaOH main extraction and 3) a 0.05 M EDTA pre-extraction followed by a 0.25 M NaOH-0.05 M EDTA main extraction. The results showed that the extraction protocol 2 was optimal for fresh activated sludge, extracting 10.8 ± 0.4 to 11.4 ± 1.2 mgP/gDW poly-P. Extraction protocols 1 and 3 extracted less than 9.4 ± 0.5 mgP/gDW poly-P. A comparison of the quantification of poly-P by 31P solution NMR and by 31P solid state NMR spectroscopy of lyophilised activated sludge showed 86 ± 9% extraction efficiency of poly-P, which confirms that the extraction protocol recovered most of the poly-P from the samples without pronounced poly-P degradation.

Halide‐Substituted Phosphacyclohexadienyl Iron Complexes: Covalent Structures vs. Ion Pairs

The coordination chemistry of phosphinines (phosphabenzenes) has been intensively investigated over the last decades, but metal complexes of halophosphinines and related halide‐substituted phosphacyclohexadienyls have remained scarce. Here, we describe the synthesis of a series of complexes [Cp*Fe(1‐F‐PC5Ph3H2)] (2‐F, Cp* = C5Me5), [Cp*Fe(1‐Cl‐PC5Ph3H2)] (2‐Cl), [Cp*Fe(PC5Ph3H2)]Br (2‐Br) and [Cp*Fe(PC5Ph3H2)]I (2‐I), which were obtained by reacting the previously reported 2,4,6‐triphenylphosphinine iron complex [K([18]crown‐6)(thf)2] [Cp*Fe(PC5Ph3H2)] (1) with electrophilic halogenating agents. To the best of our knowledge, 2‐F and 2‐Cl are the first π‐coordinated λ3‐halophosphacyclohexadienyl complexes with covalent P–X bonds (X = halogen). In the solid state 2‐Br and 2‐I show ionic structures with [Cp*Fe(PC5Ph3H2)]+ cations and separated X– anions. Anion exchange of I– in 2‐I for [BArF4]– {ArF = 3,5‐(CF3)2C6H3} affords [Cp*Fe(PC5Ph3H2)][BArF4] (2‐[BArF4]), which also displays an ionic structure. These new complexes were further characterized by solid‐state and solution 31P NMR spectroscopy, UV/Vis spectroscopy, elemental analyses, electrical conductivity measurements in solution, and DFT calculations. The resulting data indicate that 2‐F retains its covalent P–F bond in THF, fluorobenzene, and acetonitrile solution, while the remaining 2‐X complexes containing heavier halogen atoms (X = Cl, Br, and I) apparently form ion pairs in such solvents.

Influence of pH and redox on mobilization of inositol hexakisphosphate from oligotrophic lake sediment

It has been suggested that inositol hexakisphosphate (IP6) contributes to the release of phosphorus (P) from lake sediments, but a mechanistic understanding remains elusive. We investigated the potential mobilization and mineralization of myo- and scyllo-IP6 from the sediment of an oligotrophic Danish lake known to contain high concentrations of inositol phosphates. Solution 31P NMR spectroscopy was used to determine changes in myo- and scyllo-IP6 in laboratory microcosms incubated under either oxic or anoxic conditions. In addition, we incubated sediment slurries adjusted to pH between 4.9 and 6.6, with and without addition of myo-IP6, and induced redox changes by adding starch and sulfate. We observed no significant changes in myo- or scyllo-IP6 after 1 year of incubation under anaerobic conditions. A sequential extraction procedure revealed that one half of the added myo-IP6 was recovered in the humic acid fraction (acid-insoluble organic matter) and the other half in the fulvic acid fraction (acid-soluble organic matter). Reduction in redox potential by starch addition did not mobilize myo-IP6, but myo-IP6 bound to humic acids was released to the pore water when the pH was increased to ≥ 5.8. This pH-induced mobilization of IP6 occurred in parallel with increases in dissolved iron and organic matter, suggesting the release of IP6 bound to humic acids through metal bridges. We conclude that myo-IP6 mobilization from this oligotrophic lake sediment is driven by changes in pH rather than by changes in the redox potential.

Phosphorus dynamics in a tropical forest soil restored after strip mining

Background and aimsWe hypothesized that successful early ecosystem and soil development in these P-deficient soil materials will initially depend on effective re-establishment of P storage and cycling through organic matter. This hypothesis was tested in a 26-year chronosequence of seven lightly fertilized, oxidic soil materials restored to eucalypt forest communities after bauxite mining.MethodsTotal P (Pt) status, Hedley P fractions and partial chemical speciation (NaOH-EDTA extraction and analysed using solution 31P NMR spectroscopy) were determined in the restored soils.ResultsConcentrations of Pt and most Hedley fractions changed with restoration period, declined with depth and were strongly positively correlated with C and N concentrations. Biological P dominated the Labile and Intermediate P fractions while Long-term P was dominantly inorganic. Organic P concentrations in NaOH-EDTA extracts and their chemical natures were similar in restored and unburned native forest sites. Phosphomonoesters were the dominant class of organic P.ConclusionsSurprisingly rapid P accretion and fractional changes occurred over 26 years, largely in the surface soils and closely associated with organic matter status. Alkaline hydrolysis products of phosphodiesters and pyrophosphate indicated the importance of microbial P cycling. The important consequences for long-term ecosystem development and biological diversity require further study.

Characteristics of phosphorus fractions in the soils derived from sedimentary and serpentinite rocks in lowland tropical rain forests, Borneo

ABSTRACT Soil organic phosphorus (P) is an important P source for biota especially in P-limited forests. Organic P has various chemical formations which differ in bioavailability and these organic P can be degraded by phosphatase enzymes. Here, we report soil P fractions inferred from solution 31P-NMR spectroscopy and soil phosphatase activities of two tropical rain forests on contrasting parent materials; sedimentary and ultramafic igneous (serpentinite) rocks. Compared to the sedimentary soils and previous studies, P fractions of the serpentinite soils have distinctly high proportions of pyrophosphate and scyllo-inositol hexakisphosphate (scyllo-IP6). The accumulation of pyrophosphate and scyllo-IP6 may be related to strong sorptive capacity of iron oxides present in the serpentinite soils, which implies a consequent low P availability in the serpentinite soils. Mean value of soil phosphatase activities was higher in the serpentinite soils than in the sedimentary soils, suggesting that biota in these serpentinite forests depend more on soil organic P as a P source.

Synthesis and Molecular Structure of a Novel Compound Containing a Carbonate-Bridged Hexacalcium Cluster Cation Assembled on a Trimeric Trititanium(IV)-Substituted Wells-Dawson Polyoxometalate.

A novel compound containing a hexacalcium cluster cation, one carbonate anion, and one calcium cation assembled on a trimeric trititanium(IV)-substituted Wells-Dawson polyoxometalate (POM), [{Ca6(CO3)(μ3-OH)(OH2)18}(P2W15Ti3O61)3Ca(OH2)3]19- (Ca7Ti9Trimer), was obtained as the Na7Ca6 salt (NaCa-Ca7Ti9Trimer) by the reaction of calcium chloride with the monomeric trititanium(IV)-substituted Wells-Dawson POM species "[P2W15Ti3O59(OH)3]9-" (Ti3Monomer). Ti3Monomer was generated in situ under basic conditions from the separately prepared tetrameric species with bridging Ti(OH2)3 groups and an encapsulated Cl- ion, [{P2W15Ti3O59(OH)3}4{μ3-Ti(H2O)3}4Cl]21- (Ti16Tetramer). The Na7Ca6 salt of Ca7Ti9Trimer was characterized by complete elemental analysis, thermogravimetric (TG) and differential thermal analyses (DTA), FTIR, single-crystal X-ray structure analysis, and solution 183W and 31P NMR spectroscopy. X-ray crystallography revealed that the [Ca6(CO3)(μ3-OH)(OH2)18]9+ cluster cation was composed of six calcium cations linked by one μ6-carbonato anion and one μ3-OH- anion. The cluster cation was assembled, together with one calcium ion, on a trimeric species composed of three tri-Ti(IV)-substituted Wells-Dawson subunits linked by Ti-O-Ti bonds. Ca7Ti9Trimer is an unprecedented POM species containing an alkaline-earth-metal cluster cation and is the first example of alkaline-earth-metal ions clustered around a titanium(IV)-substituted POM.

Soil organic phosphorus transformation during ecosystem development: A review

Soil organic phosphorus transformation during ecosystem development exerts a crucial influence on soil fertility and ecosystem properties. This paper reviews the use of solution 31P NMR spectroscopy for characterizing organic phosphorus speciation in soil chronosequence and long-term field experiments in order to improve our understanding of the temporal changes, fundamental processes, and associated natural and anthropogenic controls of organic phosphorus transformation during long-term ecosystem evolution. Published soil chronosequence studies show that organic phosphorus compounds under aerobic conditions are dominated by phosphate monoesters (occurred mainly as inositol phosphates) followed by phosphate diesters (occurred mainly as DNA) and phosphonates, irrespective of the different parent materials, vegetation covers and climatic conditions. This contrasted markedly with wetland soils in which phosphate monoesters and diesters maintained approximately equal proportions, which is attributed to the limited reactive clay surfaces for stabilization and/or decomposition of myo-inositol hexakisphosphate under frequent anaerobic conditions. Most organic phosphorus compounds in soil chronosequences increase with age to reach a maximum and then decline with time, although the apex varies significantly among different organic phosphorus compounds and chronosequences. Variations of the potential for phosphorus stabilization resulting from mineralogical transformation, changes in phosphorus sources due to shifts in plant and microbial communities, and differences in the biological utilization of various phosphorus compounds have been suggested as three main mechanisms controlling the temporal changes in organic phosphorus species, abundance and availability during natural ecosystem development. In agricultural soils, the amounts, forms, and dynamics of organic phosphorus are determined by internal soil properties, external environmental conditions and managements, including the history and intensity of land use, different tillage practices and fertilizer treatments. These mechanisms are interlinked and more research is required to isolate both internal and external factors that regulate organic phosphorus transformation in agricultural ecosystems. Given the universal dependence on organic phosphorus for life and its critical roles in biogeochemical cycling, we put forward several open questions that need to be resolved in the future studies by emphasizing the multidisciplinary collaborations, the use of multiple analytical techniques and the establishment of quantitative organic phosphorus transformation models.

Discovery and isolation of the trans-isomers of two 1 : 2-type lanthanide-containing monolacunary Dawson-type tungstophosphates: [LnIII(α2-P2W17O61)2]17− (Ln = La, Ce)

Two novel trans-isomers of 1 : 2-type lanthanide-containing monolacunary Dawson-type tungstophosphates [Ln(α2-P2W17O61)2]17- (Ln = LaIII (1), CeIII (2)) were successfully isolated and characterized by elemental analysis, IR, TG, and 31P NMR studies. Both polyanions 1 and 2 consist of one Ln3+ ion sanwiched between two monolacunary Dawson-type tungstophosphates fragments [α2-P2W17O61]10- oriented at 180° with respect to each other. The solid-state and solution 31P NMR spectroscopy revealed that the trans-[Ce(α2-P2W17O61)2]17- species probably quickly isomerizes to the cis-isomer species in solution.

Linking the depletion of rhizosphere phosphorus to the heterologous expression of a fungal phytase in Nicotiana tabacum as revealed by enzyme-labile P and solution 31P NMR spectroscopy

Root exudation of phytase could improve the ability of plants to access organic forms of soil phosphorus (P), thereby minimizing fertilizer requirements and improving P use efficiency in agroecosystems. After 75 days growth in a high available P soil, shoot biomass and P accumulation, soil pH, and rhizosphere P depletion were investigated in Nicotiana tabacum wild-type and transgenic plant-lines expressing and exuding Aspergillus niger phytase (ex::phyA), or a null-vector control. Solution 31P NMR analysis revealed a 7% to 11% increase in orthophosphate and a comparable depletion of undefined monoester P compounds (-13 to -18%) in the rhizosphere of tobacco plants relative to the unplanted soil control. Wild-type plants had the greatest impact on the composition of rhizosphere P based on the depletion of other monoester P, polyphosphate, and phosphonate species. The depletion of phytase-labile P by ex::phyA plants was associated with decreased proportions of other monoester P, rather than myo-InsP6 as expected. Rhizosphere pH increased from 6.0 to 6.5-6.7 in transgenic plant soils, beyond the pH optimum for A. niger phyA activity (pH=5), and may explain the limited specificity of ex::phyA plants for phytate in this soil. The efficacy of single exudation traits (e.g., phytase) therefore appear to be limited in P-replete soil conditions and may be improved where soil pH matches the functional requirements of the enzyme or trait of interest.

Phosphatase activities in sediments of subtropical lakes with different trophic states

We characterized the vertical distribution of extracellular phosphatase enzymes; phosphomonoesterase (PMEase) and phosphodiesterase (PDEase) activities in sediments of three subtropical lakes were characterized by different trophic states. We then explored relationships between phosphatase activities, phosphorus (P) compounds, and microbial biomass and activity. Sediment P compounds had been characterized previously by two different methods: sequential fractionation and solution 31P NMR spectroscopy. PMEase and PDEase activities declined with depth and were correlated strongly with microbial biomass and anaerobic respiration, indicating that bacterial phosphatase dominated in these sediments and is an important step in the anaerobic breakdown of organic matter. The oligo-mesotrophic lake had higher PMEase activity and the hypereutrophic lake had higher PDEase activity, while the eutrophic lake had the lowest activities of both enzymes. Principal component analyses showed that enzyme activities were related closely to concentrations of the P forms that they degrade: PMEase activity was correlated with phosphomonoesters, while PDEase activity was correlated with phosphodiesters (including nucleic acids and phospholipids). Enzyme activities were not related to the trophic state but with the concentration P forms found in the sediment. Overall, these results provide insight into the phosphorus cycle in subtropical lake sediments by demonstrating a link between phosphatase activity, P composition, and microbial activity.

PH and Eh effects on phosphorus fate in constructed wetland's sludge surface deposit

The objective of the present study was to assess the influence of extreme pH and redox potential (Eh) conditions on phosphorus (P) retention within the surface sludge deposit layer of a vertical flow constructed wetland (VFCW) where phosphorus was captured by FeCl3 injection. Series of 27 successive batch leaching tests were conducted under acidic, alkaline or reductive conditions using a representative sludge sample taken from an 8-year old VFCW plant. Experiments were followed by monitoring the pH and Eh variations and analysing the releases of P and other selected elements into the solutions. The sludge material was also analyzed before and after leaching, using solution 31P NMR spectroscopy and sequential chemical extractions, in order to evaluate dissolutions of both organic and inorganic P-bearing species and their respective contributions to P release. The correlations between the monitored variables were analyzed and visualized through principal components analyses (PCA). Results showed a very good stability of P retention in the sludge deposit and a relatively good acid-buffering capacity of the sludge, revealing that the risk of accidental P release into the environment would be extremely low during the real plant operation.

Preliminary validation of a sequential fractionation method to study phosphorus chemistry in a calcareous soil

A sequential fractionation method proposed by Jiang and Gu (1989) distinguished three types of calcium phosphates (Ca-P) according to their different plant availabilities. Three extractants, NaHCO3, NH4Ac, and H2SO4 were used to extract Ca2-P, Ca8-P, and Ca10-P types, respectively, from soil. This sequential fractionation method was tested and modified for analyzing the P chemistry of a calcareous soil. The solubility test and the model diagrams of the stability of the major Ca-P minerals showed that NaHCO3 was able to extract brushite (Ca2-P type), and NH4Ac extracted brushite and β-tricalcium P (Ca8-P type) as well as hydroxyapatite (Ca10-P type). Therefore the P forms targeted by extraction with NH4Ac should include both Ca8-and Ca10-P types. The sum of the P extracted by all extractants in the sequential fractionation method in the calcareous soil was in agreement with the total P measured by the perchloric acid digestion method. A proportion of organic P measured by the sequential fractionation method was in agreement with the result from solution 31P NMR spectroscopy. This study showed that the modified sequential fractionation method and its target P forms would be useful for quantifying and characterizing inorganic and organic P in a calcareous soil, even though it should be used in combination with other techniques, such as solution 31P NMR spectroscopy.