Experimental removal and addition of leaf litter inputs reduces nitrate production and loss in a lowland tropical forest

Environmental perturbations such as changes in land use, climate, and atmospheric carbon dioxide concentrations may alter organic matter inputs to surface soils. While the carbon (C) cycle response to such perturbations has received considerable attention, potential responses of the soil nitrogen (N) cycle to changing organic matter inputs have been less well characterized. Changing litter inputs to surface to soils may alter the soil N cycle directly, by controlling N substrate availability, or indirectly, via interactions with soil C biogeochemistry. We investigated soil N-cycling responses to a leaf litter manipulation in a lowland tropical forest using isotopic and molecular techniques. Both removing and doubling leaf litter inputs decreased the size of the soil nitrate pool, gross nitrification rates, and the relative abundance of ammonia-oxidizing microorganisms. Gross nitrification rates were correlated with the relative abundance of ammonia-oxidizing archaea, and shifts in the N-cycling microbial community composition correlated with concurrent changes in edaphic properties, notably pH and C:N ratios. These results highlight the importance of understanding coupled biogeochemical cycles in global change scenarios and suggest that environmental perturbations that alter organic matter inputs in tropical forests could reduce inorganic N losses to surface waters and the atmosphere by limiting nitrate production.     

Soil Environmental Conditions and Microbial Build-Up Mediate the Effect of Plant Diversity on Soil Nitrifying and Denitrifying Enzyme Activities in Temperate Grasslands

Random reductions in plant diversity can affect ecosystem functioning, but it is still unclear which components of plant diversity (species number – namely richness, presence of particular plant functional groups, or particular combinations of these) and associated biotic and abiotic drivers explain the observed relationships, particularly for soil processes. We assembled grassland communities including 1 to 16 plant species with a factorial separation of the effects of richness and functional group composition to analyze how plant diversity components influence soil nitrifying and denitrifying enzyme activities (NEA and DEA, respectively), the abundance of nitrifiers (bacterial and archaeal amoA gene number) and denitrifiers (nirK, nirS and nosZ gene number), and key soil environmental conditions. Plant diversity effects were largely due to differences in functional group composition between communities of identical richness (number of sown species), though richness also had an effect per se. NEA was positively related to the percentage of legumes in terms of sown species number, the additional effect of richness at any given legume percentage being negative. DEA was higher in plots with legumes, decreased with increasing percentage of grasses, and increased with richness. No correlation was observed between DEA and denitrifier abundance. NEA increased with the abundance of ammonia oxidizing bacteria. The effect of richness on NEA was entirely due to the build-up of nitrifying organisms, while legume effect was partly linked to modified ammonium availability and nitrifier abundance. Richness effect on DEA was entirely due to changes in soil moisture, while the effects of legumes and grasses were partly due to modified nitrate availability, which influenced the specific activity of denitrifiers. These results suggest that plant diversity-induced changes in microbial specific activity are important for facultative activities such as denitrification, whereas changes in microbial abundance play a major role for non-facultative activities such as nitrification.     

Distribution of High Bacterial Taxa Across the Chronosequence of Two Alpine Glacier Forelands

Little is known about the changes in abundance of microbial taxa in relation to the chronosequence of receding glaciers. This study investigated how the abundances of ten bacterial phyla or classes varied along successional gradients in two glaciers, Ödenwinkelkees and Rotmoosferner, in the central Alps. Quantitative PCR was used to estimate the abundance of the different bacterial taxa in extended glacier chronosequences, including 10- to 160-year-old successional stages, the surface of the glacier, and a fully established soil. Actinobacteria (15–30%) was the dominant group within the chronosequences. Several taxa showed significant differences in the number of taxa-specific 16S rRNA gene copies per nanogram of DNA and/or in the ratio of taxa-specific to the total bacterial 16S rRNA gene copies (i.e., the relative abundance of the different taxa within the bacterial community) between the established soils or the glacier surface and the 10- to 160-year-old successional stages. A significantly higher proportion of Βetaproteobacteria (20%) was observed on the surface of both glaciers. However, no differences were observed between the 10- to 160-year-old successional stages in the number of taxa-specific 16S rRNA gene copies per nanogram of DNA or in the ratio of taxa-specific to the total bacterial 16S rRNA gene copies for the different taxa. Nevertheless, when the relative abundance data from all the studied taxa were combined and analyzed altogether, most of the sites could be distinguished from one other. This indicates that the overall composition of the bacterial community was more affected than the abundance of the targeted taxa by changes in environmental conditions along the chronosequences.     

Quantification of the Detrimental Effect of a Single Primer-Template Mismatch by Real-Time PCR Using the 16S rRNA Gene as an Example

We investigated the effects of internal primer-template mismatches on the efficiency of PCR amplification using the 16S rRNA gene as the model template DNA. We observed that the presence of a single mismatch in the second half of the primer extension sequence can result in an underestimation of up to 1,000-fold of the gene copy number, depending on the primer and position of the mismatch.     

DNA Extraction from Soils: Old Bias for New Microbial Diversity Analysis Methods

The impact of three different soil DNA extraction methods on bacterial diversity was evaluated using PCR-based 16S ribosomal DNA analysis. DNA extracted directly from three soils showing contrasting physicochemical properties was subjected to amplified ribosomal DNA restriction analysis and ribosomal intergenic spacer analysis (RISA). The obtained RISA patterns revealed clearly that both the phylotype abundance and the composition of the indigenous bacterial community are dependent on the DNA recovery method used. In addition, this effect was also shown in the context of an experimental study aiming to estimate the impact on soil biodiversity of the application of farmyard manure or sewage sludge onto a monoculture of maize for 15 years.     

A nitroxide-sterol derivative potently modifies cholesterol biosynthesis by normal and neoplastic guinea pig lymphocytes

Leukemic guinea pig lymphocytes (L₂ C) synthesise cholesterol in vitro at a forty-fold greater rate than normal cells. Equilibration (18 h) with lecithin or lecithin-cholesterol liposomes, respectively, enhances or suppresses sterol manufacture by normal lymphocytes but does not influence sterol production by L₂ C cells. In contrast, $\text{> 5·10}{}^9$ molecules/cell of a nitroxide-derivative of androstane, (17 β-hydroxy-4′,4′-dimethylspiro [5 α-androstan-3,2′-oxazolidin]-3′-yloxyl), commonly used as a membrane spin-probe, drastically inhibit sterol production by both normal and leukemic cells (maximum within 2 h). At $\text{< 5·10}{}^9$ molecules/cell, this sterol stimulates cholesterol synthesis. 25-Hydroxycholesterol at low concentrations also stimulates sterol manufacture, whereas high concentrations are also inhibitory in both cell types.     

In vitro analysis of varus-valgus laxity of the knee joint: Comparison of clinical evaluation with measurements using a reference motion analysis system

IntroductionNumerous measurement devices can help clinicians during the knee examination. However, manual evaluation still remains routinely used to assess the knee laxities. The present study evaluated how accurate was a clinician for a varus-valgus stress test. We compared the clinician evaluation to the objective measurement of the knee movements during the same test session.MethodsWe studied six fresh-frozen anatomical lower limbs. The clinician performed a varus-valgus stress test in extension and at 25° flexion. The limbs were equipped with intracortical pins in femur and tibia, and spherical retro-reflecting markers were glued on the pins. Objective knees movements were measured by means of a Motion Analysis^® system (Motion Analysis Corporation, Santa Rosa, CA, USA). Two statistical analyses were performed. A single sample t-test was first used to verify the required 25? flexion. Then, a multivariate anova was performed to analyse the varus-valgus laxity under the fixed factors of measurement method and flexion of the knee.ResultsThe results for varus-valgus and total laxity of the clinician always exhibited a greater variability than objective measurements of the device. Test condition is a factor of grouping differences for Valgus and for global mediolateral laxity. Statistical analysis revealed that the objective measurement was able to show a difference between extension and 25° flexion for global mediolateral laxity, whereas the clinician was not.DiscussionThe clinician was relatively accurate in his manual evaluation. However, we demonstrated that a measurement device could clearly help clinician to exhibit differences in laxity. This can be very useful to compare a knee to itself in two successive conditions, e.g., before and after a surgery.     

Chain length dependent modification of lipid organization by low levels of 25-hydroxycholesterol and 25-hydroxycholecalciferol. A laser Raman study

We have used Raman spectroscopy to investigate the thermal transitions of multibilayered liposomes composed of lecithins, i.e., dilauroyllecithin, dimyristoyllecithin, dipalmitoyllecithin, distearoyllecithin, or egg lecithin, plus 5-cholesten-3,25-diol (25-hydroxycholesterol), 25-hydroxycholecalciferol, and vitamin D3. We recorded the CH-stretching (2800-3000-cm-1) regions of the Raman spectra at various temperatures and employed plots of temperature vs. the intensity of the 2880- or 2930-cm-1 bands relative to that of the 2850-cm-1 feature, i.e., the ratios I2880/I2850 and I2930/I2850, to estimate thermal transitions. These plots show multiple discontinuities, each of which may be ascribed to a state change of a separate phase with distinctive proportions of lecithins and cholesterol derivatives. Low concentrations of 25-hydroxycholesterol and 25-OH-D3 (greater than or equal to 0.2 mol%) abolish the pretransition and split the main transitions of dilauroyllecithin (4 degrees C) and dimyristoyllecithin (23 degrees C) into two. The midpoint of the new small transition centers at about 3-4 degrees C lower than those of the respective main transitions of dilauroyllecithin and dimyristoyllecithin. A further increase in the molar ratio of 25-hydroxycholesterol and 25-hydroxycholecalciferol decreases the amplitudes of the new and the main transitions (dilauroyl- and dimyristoyllecithin). The transitions of dipalmitoyllecithin and distearoyllecithin at 2 mol % concentrations of either sterol remain unaffected. There was no splitting in the main transition of either dipalmitoyllecithin or distearoyllecithin in the presence of these sterols. The perturbing effect of the 25-hydroxysterols follows the order dilauroyllecithin greater than dimyristoyllecithin greater than dipalmitoyllecithin greater than distearoyllecithin.(ABSTRACT TRUNCATED AT 250 WORDS)