Estimating the variance of the sample mean in two-dimensional systematic sampling

This article investigates the problem of estimating the sampling error when the population mean (total) is estimated from a single two-dimensional systematic sample. In particular, two-dimensional extensions of known approximate variance estimators used in linear systematic sampling are introduced. These almost new variance estimators have the advantage of taking into account the spatial ordering of sample units and, consequently, the spatial autocorrelation among them. An investigation of their properties is carried out through a series of simulations and an empirical study.     

Profundal macrobenthos structure as a measure of long-term environmental stress in a polluted lake

Profundal macrobenthic community in a polluted lake (Lake Nemi, Italy) was analyzed in three distinct surveys from 1976 to 1984, in order to define long-term changes in environmental conditions of sediments. Profundal macrobenthos was mainly composed of Oligochaeta. Only a few Chironomidae and a few other taxa were characteristically found in the superior zone. The long-term stress, due to persistent hypolimnetic O₂ deficit, caused progressive simplification of the total community structure. This leads to a high faunal similarity among stations at different depths. The temporal trend of the community structure parameters and the significant role of some taxa (Potamothrix heuscheri, Procladius and Chaoborus flavicans) in the eutrophication process of the lake are also discussed.     

Determination of selenium content in different types of seed oils by cathodic stripping potentiometry (CSP)

Seed oils are consumed worldwide; moreover, they are used in the alimentary, cosmetic, pharmaceutical, and chemical industries. Due to their diffusion, it is interesting to investigate the presence of important micronutrients such as selenium in seed oils. The aim of this work was to develop a rapid, precise, and sensitive cathodic stripping potentiometry (CSP) method to determine the concentration of selenium in different types of seed oils. Selenium was extracted from the oily matrix by concentrated hydrochloric acid treatment at 90 degrees C. The analysis was executed by applying an electrolysis potential of -150 mV for 60 s and a constant current of -30 microA. Under these conditions, detection limits of <0.5 ng g(-1) were obtained. The method reproducibility (expressed as total RSD %) spanned from 0.2 to 0.8%. Recoveries ranged from 92.1 to 97.5%, providing evidence that selenium quantification remained unaffected by the extraction procedure described. The results obtained with the proposed method were compared with those obtained via graphite furnace atomic absorption spectroscopy (GFAAS), a common method for determining selenium. The results of the two methods agreed within 93.5-107.7%. The mean amounts of selenium found were 313.0 +/- 2.0, 458.3 +/- 1.3, 224.6 +/- 0.9, 99.5 +/- 0.8, 332.2 +/- 0.5, 144.0 +/- 0.7, and 295.5 +/- 1.2 ng g(-1), respectively, in peanut, soybean, sunflower, rice, corn, grapestone, and seed oils.     

Biocontrol of soil-borne fungal plant diseases by 2,4-diacetylphloroglucinol-producing fluorescent pseudomonads with different restriction profiles of amplified 16S rDNA

Fluorescent pseudomonads producing the antimicrobial compound 2,4-diacetylphloroglucinol (Phl) are being studied extensively for use as biocontrol agents of soil-borne fungal diseases. Some of them can produce pyoluteorin (Plt) in addition to Phl, whereas others synthesise only Phl. Here, a collection of seven Phl⁺ Plt^- pseudomonads, seven Phl⁺ Plt⁺ pseudomonads and seven Phl^- biocontrol pseudomonads were compared for protection of plant roots against fungal pathogens. The seven Phl⁺ Plt⁺ pseudomonads were identical by restriction analysis of amplified spacer ribosomal DNA (spacer ARDRA), whereas the Phl⁺ Plt^- pseudomonads and especially the Phl^- biocontrol pseudomonads were quite diverse by spacer ARDRA. Collectively, the Phl⁺ Plt^- pseudomonads proved superior to the Phl⁺ Plt⁺ pseudomonads and the Phl^- biocontrol pseudomonads for protection of tomato against Fusarium crown and root rot (in rockwool microcosms) or cucumber against Pythium damping-off (in non-sterile soil microcosms). There was no correlation between protection in vivo and inhibition of the corresponding fungal pathogen on plates. However, there was a significant correlation between the amount of Phl produced on plates and protection of tomato against Fusarium crown and root rot, but not with protection of cucumber against Pythium damping-off. Interestingly, the minority of strains unable to produce HCN, an extracellular protease, or both, were among those unable to protect plants in both pathosystems. A seedling assay was developed to compare pseudomonads for suppression of Fusarium crown and root rot in vitro, and a significant correlation was found between disease severity in vitro and in vivo. Overall, results suggest that promising biocontrol pseudomonads may be identified based on the ability to produce Phl and/or specific ARDRA-based fingerprints.     

Assessment of urea degradation rate in model wine solutions by acid urease from Lactobacillus fermentum

The specific activity (piA) of a whole cell acid urease preparation was assessed in model wine solutions at different levels of malic (M) and lactic acids, metabisulfite, ethanol, and pH by performing a central composite design. M and then pH were found to be the most controlling variables, their effects being practically coincident but of opposite sign. For urea concentrations up to approximately 1 mol m(-3) the ammonium formation rate was assumed of the pseudo-first-order with respect to urea, this being confirmed by two independent validation tests performed at 20 degrees C for as long as 24 h. In the case of real wines the effective pseudo-first-order kinetic rate constants were found to be smaller than those pertaining to the model solutions having the same wine composition and pH by a factor varying from 10 to 1000, this affecting significantly the specific urease treatment costs per liter of wine treated.     

Clinical,hematological, and biochemical findings in puppies with coronavirus and parvovirus enteritis

The clinical and laboratory findings in puppies naturally infected with canine coronavirus (CCoV) and/or canine parvovirus (CPV) were compared with findings in uninfected puppies. Lymphopenia was the only parameter related to CCoV infection that was statistically significant; vomiting, anorexia, lethargy, hemorrhagic fluid diarrhea, leukopenia, lymphopenia, thrombocytopenia, hypoglycemia, and hypoproteinemia were correlated with CPV infection.     

Physiological responses of Quercus ilex Leaves to Water Stress and Acute Ozone Exposure Under Controlled Conditions

The combined effect of water stress and ozone (O₃) on stomatal O₃ flux, damage to photosynthesis, and detoxification by biogenic volatile organic compounds (BVOC) in Quercus ilex leaves was studied. A 4-weeks O₃ exposure (250 ppb, 4 h per day) caused a reduction of photosynthesis and stomatal conductance, which was fully recovered 1 week after the end of the treatment, in well-watered and water-stressed plants. Measurements of stomatal O₃ flux revealed a low stomatal flux of the pollutant, which became minimal after stomatal closure caused by water stress. An induction of volatile monoterpenes, important compounds in the O₃ scavenging system in Q. ilex, and a burst of lipoxygenase compounds (LOX), which are released as gaseous by-products of membrane peroxidation, was observed after 2–3 weeks of O₃ fumigation. However, these compounds were also released in control leaves that were exposed to ozone only briefly, to determine stomatal O₃ flux. The low stomatal flux that occurred in water stress conditions helped avoiding permanent damage to Q. ilex leaves, although during the O₃ treatment photosynthesis was severely limited by stomatal closure. In well-watered plants, O₃ fumigation caused a noticeable increase of nocturnal stomatal conductance. If confirmed on adult plants under field conditions, this effect can imply larger flux of O₃ at night and possible detrimental effects of O₃ on leaf functions in plants exposed to high nocturnal O₃ levels.