Interaction of minerals,organic matter,and microorganisms during biogeochemical interface formation as shown by a series of artificial soil experiments

Our understanding of the interactions between minerals, organic matter, and microorganisms at so-called biogeochemical interfaces in soil is still hampered by the inherent complexity of these systems. Artificial soil maturation experiments can help to bridge a gap in complexity between simple abiotic sorption experiments and larger-scale field experiments. By controlling other soil-forming factors, the effect of a particular variable can be identified in a simplified system. Here, we review the findings of a series of artificial soil incubation experiments with the aim of revealing general trends and conclusions. The artificial soils were designed to determine the effect of mineral composition and charcoal presence on the development of abiotic and biotic soil properties during maturation. In particular, the development of soil aggregates, organic matter (OM) composition and turnover, sorption properties, and the establishment of microbial community composition and function were considered. The main objectives of the research were to determine (1) how surface properties and sorption of chemicals modify biogeochemical interfaces; (2) how much time is required to form aggregates from mixtures of pure minerals, OM, and a microbial inoculum; and (3) how the presence of different mineral and charcoal surfaces affects aggregation, OM turnover, and the development of microbial community composition.     

Carbon and hydrogen stable isotope ratios of carotenoids and beta-carotene-based dietary supplements

Considering the increasing nutritional and commercial importance of carotenoids, there is an interest in developing a reliable method for authenticity assessment of these compounds. Applying isotope ratio mass spectrometry using elemental analysis in the "combustion" (C) and "pyrolysis" (P) modes (EA-C/P-IRMS), the delta (13)C V-PDB and delta (2)H V-SMOW values of selected carotenoids and alpha/beta-carotene-based commercial dietary supplements were determined in comparison to those of synthetic and "natural" references. The delta (13)C V-PDB and delta (2)H V-SMOW values of synthetic beta-carotene samples ( n = 4), ranging from -25.3 per thousand to -26.4 per thousand and from -144 per thousand to -155 per thousand, respectively, differed clearly from the data determined for carotenoids from various natural sources, including C 3 plant material ( n = 9; delta (13)C V-PDB ranging from -28.5 per thousand to -32.8 per thousand and delta (2)H V-SMOW from -180 per thousand to -275 per thousand) and microalgae Dunaliella salina ( n = 1; delta (13)C V-PDB value of -15.6 per thousand and delta (2)H V-SMOW value of -191 per thousand). From five commercial dietary supplements under study, two revealed delta (13)C V-PDB and delta (2)H V-SMOW values in areas as found for synthetic references, and the other three had values near those of biotechnological beta-carotene produced by D. salina. The delta (13)C V-PDB and delta (2)H V-SMOW values recorded for natural lycopene ( n = 4) and lutein ( n = 5) ranged from -31.1 per thousand to -31.8 per thousand and from -180 to -201 per thousand, as well as from -28.8 per thousand to -32.2 per thousand and from -186 per thousand to -245 per thousand, respectively. Synthetic canthaxanthin ( n = 3) exhibited delta (13)C V-PDB and delta (2)H V-SMOW values ranging from -25.0 per thousand to -28.6 per thousand and from -133 per thousand to -153 per thousand, respectively. The EA-C/P-IRMS application of this study showed that the natural stable isotopic composition of carotenoids is a powerful tool for determining their origin.     

Concentrations of total glutathione and cysteine in wheat flour as affected by sulfur deficiency and correlation to quality parameters

A method for the simultaneous quantitation of total glutathione and total cysteine in wheat flour by a stable isotope dilution assay using high-performance liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) was developed. As internal standards, L-[(13)C3, (15)N]cysteine and L-gamma-glutamyl-L-[(13)C3, (15)N]cysteinyl-glycine were used. The method consisted of the extraction and reduction of flour with tris(2-carboxyethyl) phosphine after the addition of internal standards, protection of free thiol groups with iodoacetic acid, derivatization of free amino groups with dansyl chloride, and HPLC-MS/MS. The limits of detection and quantitation for glutathione were 0.75 nmol/g and 2.23 nmol/g flour, respectively. For cysteine, the limits of detection and quantitation were 0.72 nmol/g and 2.12 nmol/g flour, respectively. The developed method was found to be sensitive enough for quantitation of total glutathione and cysteine levels in wheat flour. This method was then utilized to investigate the effect of sulfur (S) deficiency on the amount of total glutathione and cysteine in flour. In S-deficient wheat, the concentrations of total glutathione and cysteine were proportional to the amount of S supplied during growth. The calculation of correlations revealed that GSH and Cys concentrations influenced the rheological dough properties and the baking performance at least as much as protein parameters. Thus, the low concentration of GSH and Cys in flour from S-deficient wheat had a similar effect on the technological properties as the altered composition of gluten proteins.     

Cold storage and laboratory incubation of intact soil cores do not reflect in-situ nitrogen cycling rates of tropical forest soils

Measurements of N transformation rates in tropical forest soils are commonly conducted in the laboratory from disturbed or intact soil cores. On four sites with Andisol soils under old-growth forests of Panama and Ecuador, we compared N transformation rates measured from laboratory incubation (at soil temperatures of the sites) of intact soil cores after a period of cold storage (at 5 °C) with measurements conducted in situ. Laboratory measurements from stored soil cores showed lower gross N mineralization and NH₄⁺ consumption rates and higher gross nitrification and NO₃⁻ immobilization rates than the in-situ measurements. We conclude that cold storage and laboratory incubation change the soils to such an extent that N cycling rates do not reflect field conditions. The only reliable way to measure N transformation rates of tropical forest soils is in-situ incubation and mineral N extraction in the field.     

DOPPLER MEASUREMENT OF HEPATIC ARTERIAL FLOW IN DOGS: TECHNIQUE AND PRELIMINARY FINDINGS

The common hepatic artery in 10 healthy adult beagles, 20 healthy pups (13 Deerhounds and seven Irish Wolfhounds), and seven dogs with either a congenital or acquired hepatic disorder was examined by duplex-Doppler ultrasonography. Peak systolic velocity (Vs), resistive index (RI), pulse rate, angle of insonation, and sample volume depth were recorded. Measurements in Beagles were made after a 24 h fast and repeated 2 h after feeding. The mean Vs and RI in fasted Beagles were 1.5 m/s (range 1.1-2.3 m/s) and 0.68 (range 0.62-0.74), respectively. Postprandially, there were no significant differences in any of these variables. Mean Vs and RI were lower in pups: 1.0 m/s (range 0.8-1.3 m/s) and 0.59 (range 0.46-0.65), respectively (P < .001). Two dogs with congenital arterioportal fistula had higher mean Vs (P < .001) and lower mean RI (P < .05) than normal pups. No significant differences were detected between normal Beagles, three dogs with portal vein thrombosis, and two dogs with acquired hepatic insufficiency. Differences in measured hepatic blood flow in dogs of different age or breed will complicate diagnostic use of hepatic arterial Doppler measurements.     

Effects of phenobarbital treatment on serum thyroxine and thyroid-stimulating hormone concentrations in epileptic dogs.

OBJECTIVE: To determine whether phenobarbital treatment of epileptic dogs alters serum thyroxine (T4) and thyroid-stimulating hormone (TSH) concentrations. DESIGN: Cross-sectional study. ANIMALS: 78 epileptic dogs receiving phenobarbital (group 1) and 48 untreated epileptic dogs (group 2). PROCEDURE: Serum biochemical analyses, including T4 and TSH concentrations, were performed for all dogs. Additional in vitro analyses were performed on serum from healthy dogs to determine whether phenobarbital in serum interferes with T4 assays or alters free T4 (fT4) concentrations. RESULTS: Mean serum T4 concentration was significantly lower, and mean serum TSH concentration significantly higher, in dogs in group 1, compared with those in group 2. Thirty-one (40%) dogs in group 1 had serum T4 concentrations less than the reference range, compared with 4 (8%) dogs in group 2. All dogs in group 2 with low serum T4 concentrations had recently had seizure activity. Five (7%) dogs in group 1, but none of the dogs in group 2, had serum TSH concentrations greater than the reference range. Associations were not detected between serum T4 concentration and TSH concentration, age, phenobarbital dosage, duration of treatment, serum phenobarbital concentration, or degree of seizure control. Signs of overt hypothyroidism were not evident in dogs with low T4 concentrations. Addition of phenobarbital in vitro to serum did not affect determination of T4 concentration and only minimally affected fT4 concentration. CONCLUSIONS AND CLINICAL RELEVANCE: Clinicians should be aware of the potential for phenobarbital treatment to decrease serum T4 and increase TSH concentrations and should use caution when interpreting results of thyroid tests in dogs receiving phenobarbital.