Do decomposing organic matter residues reduce phosphorus sorption in highly weathered soils?

Many studies have shown a reduction in P sorption in highly weathered soils when organic matter (OM) is applied, suggesting competition between OM decomposition products and P for sorption sites. However, such studies seldom consider the P released from the added OM. To delineate the effects of OM addition on P availability through sorption competition and P addition, water leachate from incubated soybean (SB) [Glycine mar (L.) Merr.] and Rhodes grass (RG) (Chloris gayana Knuth cv. Callide) was used in competitive P sorption studies both undiluted and after acidification (i.e., the fulvic acid [FA] component). Addition of two rates (0.2 and 2 mL) of SB leachate to an Oxisol significantly increased P sorption at the higher rate, while a similar trend was observed following RG leachate addition at the same rates. Extending the range of highly weathered soils examined (two Oxisols, an Ultisol, and an acidic Vertisol) resulted in no observed decrease in P sorption following addition of OM leachate. Surprisingly, SB leachate transiently increased P sorption in the two Oxisol soils. Addition of the FA component of the leachates resulted in a transient (< 6 d) decrease in P sorption in three of the four soils examined and constituted the only evidence in this study that decomposing OM residues reduced P sorption. This research provides further evidence contradicting the long held assumption that inhibition of P sorption by dissolved organic compounds, derived from decomposing OM, is responsible for increased P phytoavailability when P fertilizer and OM are applied together.

The rat Na+-sulfate cotransporter rNaS2: functional characterization, tissue distribution, and gene (slc13a4) structure

Inorganic sulfate is essential for numerous functions in mammalian physiology. In the present study, we characterized the functional properties of the rat Na+-sulfate cotransporter NaS2 (rNaS2), determined its tissue distribution, and identified its gene (slc13a4) structure. Expression of rNaS2 protein in Xenopus oocytes led to a Na+-dependent transport of sulfate that was inhibited by phosphate, thiosulfate, tungstate, selenate, oxalate, and molybdate, but not by citrate, succinate, or DIDS. Transport kinetics of rNaS2 determined a K-M for sulfate of 1.26 mM. Na+ kinetics determined a Hill coefficient of n=3.0 +/- 0.7, suggesting a Na+:SO42- stoichiometry of 3:1. rNaS2 mRNA was highly expressed in placenta, with lower levels found in the brain and liver. slc13a4 maps to rat chromosome 4 and contains 17 exons, spanning over 46 kb in length. This gene produces two alternatively spliced transcripts, of which the transcript lacking exon 2 is the most abundant form. Its 5' flanking region contains CAAT- and GC-box motifs and a number of putative transcription factor binding sites, including GATA-1, SP1, and AP-2 consensus sequences. This is the first study to characterize rNaS2 transport kinetics, define its tissue distribution, and resolve its gene (slc13a4) structure and 5' flanking region.

Functional characterization and genomic organization of the human Na+-sulfate cotransporter hNaS2 gene (SLC13A4)

Sulfate plays an essential role in human growth and development. Here, we characterized the functional properties of the human Na+-sulfate cotransporter (hNaS2), determined its tissue distribution, and identified its gene (SLC13A4) structure. Expression of hNaS2 protein in Xenopus oocytes led to a Na+-dependent transport of sulfate that was inhibited by thiosulfate, phosphate, molybdate. selenate and tungstate, but not by oxalate, citrate, succinate, phenol red or DIDS. Transport kinetics of hNaS2 determined a K, for sulfate of 0.38 mM, suggestive of a high affinity sulfate transporter. Na+ kinetics determined a Hill coefficient of 1.6 +/- 0.6, suggesting a Na: SO42- stoichiometry of 2:1. hNaS2 mRNA was highly expressed in placenta and testis, with intermediate levels in brain and lower levels found in the heart, thymus, and liver. The SLC13A4 gene contains 16 exons, spanning over 47 kb in length. Its 5'-flanking region contains CAAT- and GC-box motifs, and a number of putative transcription factor binding sites, including GATA-1, AP-1, and AP-2 consensus sequences. This is the first study to characterize hNaS2 transport kinetics, define its tissue distribution, and resolve its gene (SLC13A4) structure and 5' flanking region. (C) 2004 Elsevier Inc. All rights reserved.

Synthesis and magnetic properties of Fe-Mn-Cr multinuclear complexes with 4-amino-1,2,4-triazole and oxalate ligands

A multinuclear Fe-Mn-Cr complex with 4-amino-1,2,4-triazole (NH2trz) and oxalate (ox) ligands has been synthesized successfully. The formula of the [Fe(NH2trz)3][ClO4][MnCr(ox)3].4H2O complex has been obtained based on the metal and C, H, N contents. The presence of water molecules, metal-ligand bonding and bridge ligand in the multinuclear complex has been confirmed by its infrared spectrum. The compound crystallizes in the hexagonal system with cell parameters of a = b = 18.695 Å and c = 57.351 Å. The compound shows a gradual spin crossover for iron(II) in the [Fe(NH2trz)3]2+ with transition temperature (T1/2) of 205 K. The antiferromagnetic interaction between Cr(III) and Mn(II) ions in the [MnCr(ox)3]n n- network is observed from the Weiss constant (θ) of –2.3 K.

Phénotypage métabolique du coeur sain et malade basé sur l'analyse d'isotopomères de masse marqués au carbone 13 : implications du citrate

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Phénotypage métabolique du coeur sain et malade basé sur l'analyse d'isotopomères de masse marqués au carbone 13 : implications du citrate.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Geochemistry of sediment core HE337/001-1, North Sea

Reactive iron (oxyhydr)oxide minerals preferentially undergo early diagenetic redox cycling which can result in the production of dissolved Fe(II), adsorption of Fe(II) onto particle surfaces, and the formation of authigenic Fe minerals. The partitioning of iron in sediments has traditionally been studied by applying sequential extractions that target operationally-defined iron phases. Here, we complement an existing sequential leaching method by developing a sample processing protocol for d56Fe analysis, which we subsequently use to study Fe phase-specific fractionation related to dissimilatory iron reduction in a modern marine sediment. Carbonate-Fe was extracted by acetate, easily reducible oxides (e.g. ferrihydrite and lepidocrocite) by hydroxylamine-HCl, reducible oxides (e.g. goethite and hematite) by dithionite-citrate, and magnetite by ammonium oxalate. Subsequently, the samples were repeatedly oxidized, heated and purified via Fe precipitation and column chromatography. The method was applied to surface sediments collected from the North Sea, south of the Island of Helgoland. The acetate-soluble fraction (targeting siderite and ankerite) showed a pronounced downcore d56Fe trend. This iron pool was most depleted in 56Fe close to the sediment-water interface, similar to trends observed for pore-water Fe(II). We interpret this pool as surface-reduced Fe(II), rather than siderite or ankerite, that was open to electron and atom exchange with the oxide surface. Common extractions using 0.5 M HCl or Na-dithionite alone may not resolve such trends, as they dissolve iron from isotopically distinct pools leading to a mixed signal. Na-dithionite leaching alone, for example, targets the sum of reducible Fe oxides that potentially differ in their isotopic fingerprint. Hence, the development of a sequential extraction Fe isotope protocol provides a new opportunity for detailed study of the behavior of iron in a wide-range of environmental settings.

Pore water measurements of sediment cores from the Helgoland mud area, North Sea

Iron reduction in subseafloor sulfate-depleted and methane-rich marine sediments is currently a subject of interest in subsurface geomicrobiology. While iron reduction and microorganisms involved have been well studied in marine surface sediments, little is known about microorganisms responsible for iron reduction in deep methanic sediments. Here, we used quantitative PCR (Q-PCR)-based 16S rRNA gene copy numbers and pyrosequencing-based relative abundances of bacteria and archaea to investigate covariance between distinct microbial populations and specific geochemical profiles in the top 5 m of sediment cores from the Helgoland mud area, North Sea. We found that gene copy numbers of bacteria and archaea were specifically higher around the peak of dissolved iron in the methanic zone (250-350 cm. The higher copy numbers at these depths were also reflected by the relative sequence abundances of members of the candidate division JS1, methanogenic and Methanohalobium/ANME-3 related archaea. The distribution of these populations was strongly correlated to the profile of pore-water Fe2+ while that of Desulfobacteraceae corresponded to the pore-water sulfate profile. Furthermore, specific JS1 populations also strongly co-varied with the distribution of Methanosaetaceae in the methanic zone. Our data suggest that the interplay among JS1 bacteria, methanogenic archaea and Methanohalobium/ANME-3-related archaea may be important for iron reduction and methane cycling in deep methanic sediments of the Helgoland mud area and perhaps in other methane-rich depositional environments. .