Mineralogy and petrology of comet 81P/Wild 2 nucleus samples

The bulk of the comet 81P/Wild 2 (hereafter Wild 2) samples returned to Earth by the Stardust spacecraft appear to be weakly constructed mixtures of nanometer-scale grains, with occasional much larger (over 1 micrometer) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal, and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in comet Wild 2 requires a wide range of formation conditions, probably reflecting very different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and the absence of hydrous phases indicate that comet Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require radial transport in the early protoplanetary disk.     

Effects of Fruit Numbers and Plant Status on Fruit Size in the Strawberry

Abstract

Based on yield and fruit size data from a number of experiments implying effects of nitrogen nutrition, drip-irrigation, plant material and planting times, and including cultivars “Dania”, “Elsanta”, “Bogota” and “Pandora”, distinct negative relationships between fruit size and fruit number per plant or fruit/leaf ratio, were established. Apart from that, fruit size may be affected by plant material and cropping year, the latter probably related to weather conditions. Achene spacing was influenced by year, and increased by irrigation under drought conditions. Relevance of factors influencing fruit size is discussed. It is concluded that an increase in the number of flower meristems (or a more vigorous vegetative growth) might aggravate internal competition, which in turn impairs flower development, resulting in a reduced flower quality and consequently smaller fruits.     

Evaluation of Soil Temperature Moderating and Moisture Conserving Effects of Various Mulches during a Growing Season

Abstract

The seven mulches investigated affected soil temperature throughout the season compared with bare soil. The degree of temperature moderation varied depending on whether the temperature trend was increasing, relatively constant or decreasing. The organic mulches, wood chips and silage, as well as spun polypropylene covered with wood chips kept the soil temperature cooler compared with bare soil until middle of August. During periods of soil warming, spun polypropylene and paper reduced soil temperature. Soil under black plastic had a higher mean temperature than bare soil throughout the season. Degradable plastic increased soil temperature, but only to a small extent. The organic mulches conserved more moisture than any other of the materials evaluated, although during July soil moisture contents were significantly higher under all mulches compared with bare soil.     

Evaluation of nonstarch polysaccharides and oligosaccharide content of different soybean varieties (Glycine max) by near-infrared spectroscopy and proteomics

A total of 832 samples of soybeans were screened by near-infrared (NIR) reflectance spectroscopy, to identify soybean samples with a lower content of oligosaccharides and nonstarch polysaccharides (NSP). Of these, 38 samples were identified on the basis of variation in protein content and agronomic value and submitted to high-resolution NIR spectroscopy. On the basis of the NIR data, 12 samples were further selected for chromatographic characterization of carbohydrate composition (mono-, di-, and oligosaccharides and NSP). Their soluble proteins were separated by two-dimensional gel electrophoresis (2DE). Using partial least-squares regression (PLSR), it was possible to predict the content of total NSP from the high-resolution NIR spectra, suggesting that NIR is a suitable and rapid nondestructive method to determine carbohydrate composition in soybeans. The 2DE analyses showed varying intensities of several proteins, including the glycinin G1 precursor. PLSR analysis showed a negative correlation between this protein and insoluble NSP and total uronic acid (UA).     

A method for determining microbially available N and P in an organic soil

Summary A bioassay of microbially available soil N and P is described. It is based on the addition of glucose together with N or P to soil, followed by monitoring of the respiration rate. The addition of glucose + N resulted in an immediate increase in the soil respiration rate followed by a short period of exponential increase, reflecting the growth of microorganisms on the added substrate. The exponential phase levelled off, when lack of P prevented further growth of the soil microorganisms. The soil respiration rate then remained constant for several hours before decreasing, when glucose became limiting. The addition of glucose + P resulted in a lower plateau of the soil respiration rate, indicating that microbial growth was more limited by N than P in this forest soil (0.28 and 0.79 mg CO₂ g^-1 organic matter h^-1, respectively). Additions of the limiting nutrient resulted in a proportional increase in the constant level of the soil respiration rate. This was used to calculated the increase in the soil respiration rate per mg N (0.71 mg CO₂ h^-1) or mg P (4.6 mg CO₂ h^-1) added to this particular soil. Microbially available N was then calculated in two ways from the regression equation (0.15 or 0.40 mg g^-1 organic matter) and P (0.13 or 0.17 mg g^-1 organic matter). A comparison with 2 M KCl extraction showed that in nutrient-poor forest soils the microbially available N was 6.3 or 18.5 times higher than the KCl extractable N.     

Tropical savannah woodland: effects of experimental fire on soil microorganisms and soil emissions of carbon dioxide

Burning of the vegetation in the African savannahs in the dry season is widespread and may have significant effects on soil chemical and biological properties. A field experiment in a full factorial randomised block design with fire, ash and extra grass biomass as main factors was carried out in savannah woodland of the Gambella region in Ethiopia. The microbial biomass C (C_mic) was 52% (fumigation-extraction) and 20% (substrate-induced respiration) higher in burned than unburned plots 12 d after burning. Both basal respiration and potential denitrification enzyme activity (PDA) immediately responded to burning and increased after treatment. However, in burned plots addition of extra biomass (fuel load) led to a reduction of C_mic and PDA due to enhanced fire temperature. Five days after burning, there was a short-lived burst in the in situ soil respiration following rainfall, with twice as high soil respiration in burned than unburned plots. In contrast, 12 d after burning soil respiration was 21% lower in the burned plots, coinciding with lower soil water content in the same plots. The fire treatment resulted in higher concentrations of dissolved organic C (24-85%) and nitrate (47-76%) in the soil until 90 d after burning, while soil NH₄⁺-N was not affected to the same extent. The increase in soil NO₃⁻-N but not NH₄⁺-N in the burned plots together with the well-aerated soil conditions indicated that nitrifying bacteria were stimulated by fire and immediately oxidised NH₄⁺-N to NO₃⁻-N. In the subsequent rainy season, NO₃⁻-N and, consequently, PDA were reduced by ash deposition. Further, C_mic was lower in burned plots at that time. However, the fire-induced changes in microbial biomass and activity were relatively small compared to the substantial seasonal variation, suggesting transient effects of the low severity experimental fire on soil microbial functioning.     

Polycyclic aromatic compounds and microtox® acute toxicity in contaminated sediments in Sweden

Limnic and brackish aquatic sediments from contaminated locations in Sweden were analysed for polycyclic aromatic compounds (PACs) and tested for acute aquatic toxicity. The organic compounds were analysed in solvent-extractable and alkaline-treated fractions to complete the analysis of a set of priority pollutants according to the Swedish EPA. Additionally, the acute toxicity was measured by the solid phase Microtox test. The measured effects were correlated with sedimentological and chemical parameters. Analysis revealed no indication of a contribution of PACs to the acute sediment toxicity in highly contaminated sediments, with concentrations in the range of 11.3-307 μg SPAC_37/39/g dry matter. Despite a high ranking of 3 to 5 within the Swedish EPA list for coastal sediments, the acute toxicity results indicate a very low bioavailability of the analysed PACs from the creosote and combustion-contaminated sediments. A correlation of acute toxicity to elemental sulfur was indicated.     

Relationship between N immobilization and volatile fatty acids in soil after application of pig and cattle slurry

Summary A laboratory study was performed to determine decomposition of fatty acids and mineralization of C and N from slurries in soil. Fatty acids present in slurries decomposed within 1–2 days at 25°C in soil. Parallel to the fatty acid decomposition, immobilization of N was measured in soil. The correlation between the initial fatty acid concentrations in the slurries and the amounts of N immobilized were found to be highly significant (R ²=0.97). It was concluded that fatty acids act as an easily decomposable C source for microorganisms and cause immobilization of N. Immobilization of N was followed by a curvilinear mineralization of N in all slurrytreated soils. Despite mineralization, only fresh pig slurry and anaerobically digested pig slurry showed a net release of N over 70 days whereas cattle slurry and anaerobically fermented pig slurry did not. The percentage of slurry C evolved during 70 days was fresh pig slurry, 65%; anaerobically fermented pig slurry, 48%; anaerobically digested pig slurry, 45%; and anaerobically fermented cattle slurry, 42%.     

Quantitative liquid chromatographic method using fluorescence detection for determining zearalenone and its metabolites in blood plasma and urine

The liquid chromatographic (LC) method described, suitable for use with both blood plasma and urine, is applicable for determination of zearalenone and alpha-zearalenol at levels as low as 0.5 ng/mL plasma and 5 ng/mL urine. The sample is incubated overnight with beta-glucuronidase to analyze for both conjugated and unconjugated forms of zearalenone. The next day, the sample is acidified with H3PO4, extracted with chloroform, and evaporated to dryness. The residue is dissolved in toluene and loaded onto a silica gel cartridge which is washed with toluene and eluted with toluene-acetone (88 + 12). The eluate is evaporated, and the residue is dissolved in chloroform, extracted with 0.18M NaOH, neutralized with H3PO4, and re-extracted with chloroform. The chloroform extract is evaporated, dissolved in mobile phase for LC, and injected onto a normal phase column under the following chromatographic conditions: mobile phase of water-saturated dichloromethane containing 2% 1-propanol, and fluorescence detector, excitation wave-length 236 nm, and 418 nm cut-off emission filter. Recoveries of zearalenone and its metabolites from blood plasma and urine are 80-89% in the range 2.0-10 ng standard/mL plasma, and 81-90% in the range 10-30 ng standard/mL urine. This method was used to analyze blood and urine samples from a pig fed zearalenone-contaminated feed (5 mg/kg), corresponding to 80 micrograms/kg body weight. Zearalenone was rapidly metabolized to alpha-zearalenol, which appeared in the blood only 30 min after feeding. Almost all zearalenone and alpha-zearalenol was found conjugated with glucuronic acid in both blood plasma and urine.     

Theoretical model of the abiotic component of soil CO2 tracer efflux in C pulse-labeling experiments on plant-soil systems

For measurement of the time lag between photosynthesis and CO₂ efflux from soil, the carbon isotope pulse-labeling technique is considered as the most suitable. However, an interference from the abiotic tracer CO₂ component is identified as a key difficulty for obtaining accurate results with this technique. Guidelines on how to reduce this interference are therefore urgently needed. The flux of abiotic ¹³CO₂ tracer into soil during the labeling stage, and its return to atmosphere during the monitoring stage was modeled numerically, and the labeling stage also analytically. The controls of the abiotic interference were investigated using these models. The amount of the abiotic tracer component and the time distribution of its rate of return to the atmosphere, were predicted by these models. The main model parameters were D_m (=the ratio between the soil ¹³CO₂ diffusivity and the retardation factor), and the ¹³CO₂ concentration at the soil-atmosphere interface during the labeling stage (S₁₃), while background ¹³CO₂ soil production parameters were unnecessary. The presented models guide the selection of experimental parameters for minimization of the abiotic interference. With parameterization for a particular case, the present numerical model provides a preliminary order-of-magnitude estimate of the abiotic component, which would indicate if this interference is of significance.