Differential Nutrient Limitation of Soil Microbial Biomass and Metabolic Quotients (qCO2): Is There a Biological Stoichiometry of Soil Microbes?

Background

Variation in microbial metabolism poses one of the greatest current uncertainties in models of global carbon cycling, and is particularly poorly understood in soils. Biological Stoichiometry theory describes biochemical mechanisms linking metabolic rates with variation in the elemental composition of cells and organisms, and has been widely observed in animals, plants, and plankton. However, this theory has not been widely tested in microbes, which are considered to have fixed ratios of major elements in soils.

Methodology/Principal Findings

To determine whether Biological Stoichiometry underlies patterns of soil microbial metabolism, we compiled published data on microbial biomass carbon (C), nitrogen (N), and phosphorus (P) pools in soils spanning the global range of climate, vegetation, and land use types. We compared element ratios in microbial biomass pools to the metabolic quotient qCO₂ (respiration per unit biomass), where soil C mineralization was simultaneously measured in controlled incubations. Although microbial C, N, and P stoichiometry appeared to follow somewhat constrained allometric relationships at the global scale, we found significant variation in the C∶N∶P ratios of soil microbes across land use and habitat types, and size-dependent scaling of microbial C∶N and C∶P (but not N∶P) ratios. Microbial stoichiometry and metabolic quotients were also weakly correlated as suggested by Biological Stoichiometry theory. Importantly, we found that while soil microbial biomass appeared constrained by soil N availability, microbial metabolic rates (qCO₂) were most strongly associated with inorganic P availability.

Conclusions/Significance

Our findings appear consistent with the model of cellular metabolism described by Biological Stoichiometry theory, where biomass is limited by N needed to build proteins, but rates of protein synthesis are limited by the high P demands of ribosomes. Incorporation of these physiological processes may improve models of carbon cycling and understanding of the effects of nutrient availability on soil C turnover across terrestrial and wetland habitats.     

Is the Effect of Aerobic Exercise on Cognition a Placebo Effect?

A number of studies and meta-analyses conclude that aerobic fitness (walking) interventions improve cognition. Such interventions typically compare improvements from these interventions to an active control group in which participants engage in non-aerobic activities (typically stretching and toning) for an equivalent amount of time. However, in the absence of a double-blind design, the presence of an active control group does not necessarily control for placebo effects; participants might expect different amounts of improvement for the treatment and control interventions [1]. We conducted a large survey to explore whether people expect greater cognitive benefits from an aerobic exercise intervention compared to a control intervention. If participants expect greater improvement following aerobic exercise, then the benefits of such interventions might be due in part to a placebo effect. In general, expectations did not differ between aerobic and non-aerobic interventions. If anything, some of the results suggest the opposite (e.g., respondents expected the control, non-aerobic intervention to yield bigger memory gains). These results provide the first evidence that cognitive improvements following aerobic fitness training are not due to differential expectations.     

A Pine Is a Pine and a Spruce Is a Spruce – The Effect of Tree Species and Stand Age on Epiphytic Lichen Communities

With an increasing demand for forest-based products, there is a growing interest in introducing fast-growing non-native tree species in forest management. Such introductions often have unknown consequences for native forest biodiversity. In this study, we examine epiphytic lichen species richness and species composition on the trunks of non-native Pinus contorta and compare these to the native Pinus sylvestris and Picea abies in managed boreal forests in northern Sweden across a chronosequence of age classes. Overall, we recorded a total of 66,209 lichen occurrences belonging to 57 species in the 96 studied forest stands. We found no difference in species richness of lichens between stands of P. contorta and P. sylvestris, but stands of P. abies had higher total species richness. However, species richness of lichens in stands of P. abies decreased with increasing stand age, while no such age effect was detected for P. contorta and P. sylvestris. Lichen species composition progressively diverged with increasing stand age, and in 30-year-old stands all three tree species showed species-specific assemblages. Epiphytic lichen assemblages in stands of 30-year-old P. contorta were influenced by greater basal area, canopy closure, and average diameter at breast height, P. abies stands by higher branch density and canopy closure, and stands of P. sylvestris by greater bark crevice depth. Differences in lichen species richness and composition were mainly explained by canopy closure and habitat availability, and the greater canopy closure in mature P. abies stands promoted the colonization and growth of calicioid lichen species. Our results indicate that the non-native P. contorta have similar species richness as the native P. sylvestris. The main difference in lichen species richness and composition is between P. abies and Pinus spp. in managed forests of boreal Sweden.     

Socioeconomic Differentials Between HIV Caregivers and Noncaregivers: Is There a Selection Effect? A Case of Older People Living in Nairobi City Slums

This article seeks to investigate the association between caregiving to someone with an HIV-related illness and the socioeconomic status of the caregiver using a population-based survey of 1,587 older people living in Nairobi slums. Findings indicate significant differences in living arrangements, wealth, income, and expenditure between HIV caregivers and noncaregivers. HIV caregivers lived in larger households and were also more likely to live in households with a large number of children younger than the age of 15 years. Whereas a high proportion of HIV caregivers were ranked highly in terms of wealth status, differences in per capita income and expenditure were not significant when household size and other confounders were accounted for. The financial costs associated with caring for someone with a chronic illness and the reliance on family members with financial ability for material support, a common feature of African extended family systems, may account for the relative economic advantage of HIV caregivers.     

Is Mating Different in Monogamous Species? The Midas Cichlid Fish as a Case Study

Monogamous species are typically sexually isomorphic, pair wellbefore spawning is imminent, take much time to pair, are discerningabout pairing, and appear to weigh multiple sources of informationabout species, sex, and quality of mate. The monogamous andpolychromatic Midas cichlid (Cichlasoma citrinellum) distinguishedbetween its own and a highly similar heterospecific behind aone-way mirror only when visual and chemical cues matched. Likewise,recognition of sex was hindered when interaction was precluded,even in the presence of chemical cues. Female choice of matewas most strongly influenced by the "normal, " primitive, colorand to a lesser degree by color of parents and siblings, makingit difficult to account for positive color-assortative matingin the field. Females also selected the largest and the mostaggressive males; size predicted a good defender of territory,and aggressiveness foretold effective protection of the young.Males, however, were not choosy. Pair formation features muchaggression between the large male and smaller female, and gold-coloredmorphs (G) dominate normal (N) ones. That made it difficultfor an N female to pair with a G male; using an N female thesame size as the G male, however, resulted in the usual proportionof successful pairings. I propose three testable models of paircompatibility: complementarity, parity, and maximum male aggressiveness.     

Baseline Assessment of Mesophotic Reefs of the Vitória-Trindade Seamount Chain Based on Water Quality,Microbial Diversity,Benthic Cover and Fish Biomass Data

Seamounts are considered important sources of biodiversity and minerals. However, their biodiversity and health status are not well understood; therefore, potential conservation problems are unknown. The mesophotic reefs of the Vitória-Trindade Seamount Chain (VTC) were investigated via benthic community and fish surveys, metagenomic and water chemistry analyses, and water microbial abundance estimations. The VTC is a mosaic of reef systems and includes fleshy algae dominated rhodolith beds, crustose coralline algae (CCA) reefs, and turf algae dominated rocky reefs of varying health levels. Macro-carnivores and larger fish presented higher biomass at the CCA reefs (4.4 kg per frame) than in the rhodolith beds and rocky reefs (0.0 to 0.1 kg per frame). A larger number of metagenomic sequences identified as primary producers (e.g., Chlorophyta and Streptophyta) were found at the CCA reefs. However, the rocky reefs contained more diseased corals (>90%) than the CCA reefs (~40%) and rhodolith beds (~10%). Metagenomic analyses indicated a heterotrophic and fast-growing microbiome in rocky reef corals that may possibly lead to unhealthy conditions possibly enhanced by environmental features (e.g. light stress and high loads of labile dissolved organic carbon). VTC mounts represent important hotspots of biodiversity that deserve further conservation actions.     

The Biodegradation of Poly-β-Hydroxybutyrate (PHB) by a Model Soil Community: The Effect of Cultivation Conditions on the Degradation Rate and the Physicochemical Characteristics of PHB

The biodegradation of films made of poly--hydroxybutyrate (PHB) with a molecular mass of 1500 kDa was studied using a model soil community in the presence and absence of nitrate and at different concentrations of oxygen in the gas phase. The biodegradation of PHB was investigated with respect to changes in its molecular mass, crystallinity, and some mechanical properties.     

Is There Any Effect on Smell and Taste Functions with Levothyroxine Treatment in Subclinical Hypothyroidism?

Subclinical hypothyroidism has been accused for coronary heart disease, lipid metabolism disorders, neuropsychiatric disorders, infertility or pregnancy related problems with various strength of evidence. Currently there is insufficient knowledge about olfaction and taste functions in subclinical hypothyroidism. Aim of the present study is to investigate the degree of smell and taste dysfunction in patients with subclinical hypothyroidism. 28 subclinical hypothyroid patients, and 31 controls enrolled in the prospective study in Istanbul, Turkey. Subclinical hypothyroid patients were treated with L-thyroxine for 3 months. Psychophysiological olfactory testing was performed using odor dispensers similar to felt-tip pens (“Sniffin’ Sticks”, Burghart, Wedel, Germany). Taste function tests were made using "Taste Strips" (Burghart, Wedel, Germany) which are basically tastant adsorbed filter paper strip. Patients scored lower on psychophysical olfactory tests than controls (odor thresholds:8.1±1.0 vs 8.9±1.1, p = 0.007; odor discrimination:12.4±1.3 vs 13.1±0.9, p = 0.016; odor identification:13.1±0.9 vs 14.0±1.1, p = 0.001; TDI score: 33.8±2.4 vs 36.9±2.1, p = 0.001). In contrast, results from psychophysical gustatory tests showed only a decreased score for “bitter” in patients, but not for other tastes (5.9±1.8 vs 6.6±1.0, p = 0.045). Three month after onset of treatment olfactory test scores already indicated improvement (odor thresholds:8.1±1.0 vs 8.6±0.6, p<0.001; odor discrimination:12.4±1.31 vs 12.9±0.8, p = 0.011; odor identification:13.1±0.9 vs 13.9±0.8, p<0.001; TDI scores:33.8±2.4 vs 35.5±1.7, p<0.001) respectively. Taste functions did not differ between groups for sweet, salty and, sour tastes but bitter taste was improved after 3 months of thyroxin substitution (patients:5.9±1.8 vs 6.6±1.2, p = 0.045). Correlation of changes in smell and taste, with thyroid function test were also evaluated. TSH, fT4 were found have no correlation with smell and taste changes with treatment. However bitter taste found positively correlated with T3 with treatment(r: 0.445, p: 0.018). Subclinical hypothyroid patients exhibited a significantly decreased olfactory sensitivity; in addition, bitter taste was significantly affected. Most importantly, these deficits can be remedied on average within 3 months with adequate treatment.     

Biomass storage and stand structure in a conservation unit in the Atlantic Rainforest—The role of big trees

This study represents a small-scale approach to forest structure and biomass in the Atlantic Rainforest in Brazil and provides information on an ecosystem in which there still is a lack of data in this regard.The project was carried out in the National Park “Serra dos Orgãos” in the state of Rio de Janeiro, which is one of the largest remnants of continuous forest in this area. This forest is marked by a mosaic of forest types differing in tree composition and structure. Within this heterogeneous habitat the stand structure in three investigation plots was assessed to estimate the above-ground dry biomass (AGB) for all trees with a dbh ≥ 5 cm.This study indicates the structural diversity of the Atlantic Rainforest. Trees with a dbh > 30 cm were represented by 6% of all sampled individuals (18 out of 318 trees), but contributed 72% of total estimated AGB. The results suggest that big trees in the Atlantic Rainforest may contribute more into total AGB as reported for other tropical rainforests. Small-scale structural approaches like this study are able to form an initiating framework of more detailed results and help to improve estimates on biomass amounts and therefore on carbon storage capacity.     

The Effect of Ultracentrifugation on Fine Structure and α-Amylase Production in Barley Aleurone Cells

Ultracentrifugation of barley aleurone cells results in the stratification of organelles thus allowing for a quantitation of those organelles. Gibberellic acid (GA₃)-stimulated α-amylase production in stratified cells is reduced by centrifugation at gravitational forces greater than 40,000g. Forces below 30,000g do not affect GA₃-stimulated α-amylase production although stratification of organelles occurs at these forces. The ability of centrifuged cells to respond maximally to GA₃ by producing α-amylase is related to the degree of redistribution of organelles within these cells. Thus, recovery of cells from centrifugation at forces below 30,000g is rapid, while recovery from forces above 40,000g is slow.     

Effect of Cross-Linking Methods on Structure and Properties of Poly(ε-caprolactone) Stabilized Hydrogels Containing Biopolymers

Different dense and porous biodegradable matrices based on solely atelocollagen, or with different atelocollagen and hyaluronic acid derivative ratios, were obtained by varying feeding formulations, cross-linking reaction parameters, and preparative protocols. The compositions and methods for forming hydrogels through a combination of physical and chemical cross-linking processes are provided. The chemical cross-linking was mainly mediated by a synthetic component, a poly(ε-caprolactone) reactive derivative, aiming the development of new hybrid hydrogels with tailored characteristics by an appropriate use of the advantages offered by the included natural and synthetic components and the selection of the preparative procedure. The structure and morphology of the 3D hybrid materials were comparatively investigated by means of Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and environmental scanning electron microscopy (ESEM). FTIR and XRD analysis showed no signs of collagen denaturation during the formation of 3D structures. The influence of various factors, such as the chemical composition of the resulted hydrogels and their morphology, on water uptake and water vapor sorption, mechanical behavior, as well as on in vitro degradation characteristics, was systematically investigated. The experimental results point on the advantage offered by the high and modular physicochemical stability of the ternary hydrogels cross-linked by combined approaches. All newly developed materials show no hemolytic effect, which recommends them for potential biomedical applications.     

Is There a Threshold Concentration of Cat Allergen Exposure on Respiratory Symptoms in Adults?

Background and Objective

Cat allergen concentrations higher than 8 μg/g in settled house dust, have been suggested to provoke exacerbation of allergic respiratory symptoms. However, whether the 8μg/g of indoor cat allergen concentration is indeed the minimal exposure required for triggering the asthma related respiratory symptoms or the development of sensitization has not yet been confirmed. We studied the associations between domestic cat allergen concentrations and allergic symptoms in the European Community Respiratory Health Survey II, with the aim of confirming this suggested threshold.

Methods

Cat allergen concentrations were measured in the mattress dust of 3003 participants from 22 study centres. Levels of specific immunoglobulin E to cat allergens were measured in serum samples using an immunoassay. Information on allergic symptoms, medication use, home environment and smoking was obtained from a face-to-face interview.

Results

Domestic cat allergen concentrations were not associated with allergic/ asthmatic symptoms in the entire study population, nor in the subset sensitized to cat allergen. We also found no association among individuals exposed to concentrations higher than 8 μg/g. However, exposure to medium cat allergen concentrations (0.24-0.63 μg/g) was positively associated with reported asthmatic respiratory symptoms in subjects who have experienced allergic symptoms when near animals.

Conclusions

The proposed 8 μg/g threshold of cat allergen concentrations for the exacerbation of allergic/ respiratory symptoms was not confirmed in a general European adult population. Potential biases attributable to avoidance behaviours and an imprecise exposure assessment cannot be excluded.     

Is There an Association between Long-Term Sick Leave and Disability Pension and Unemployment beyond the Effect of Health Status? – A Cohort Study

Background

Studies have shown that long-term sick leave is a strong predictor of disability pension. However, few have aimed to disentangle the effect of sick leave and of health status.The objective of this study was to investigate whether there is an association between long-term sick leave and disability pension and unemployment, when taking health status into account.

Methods/Principal Findings

The study was based on the Stockholm Public Health Cohort, restricted to 13,027 employed individuals (45.9% men) aged 18–59 in 2002 and followed until 2007.Hazard ratios (HR) with 95% Confidence Interval (CI) were estimated by Cox regression models adjusting for socio-demographic factors and five measures of health status.Having been on long-term sick leave increased the risk of disability pension (HR 4.01; 95% CI 3.19–5.05) and long-term unemployment (HR 1.45; 95% CI 1.05–2.00), after adjustment for health status. The analyses of long-term sick leave due to specific illness showed that the increased risk for long-term unemployment was confined to the group on sick leave due to musculoskeletal (HR 1.70 95% CI 1.00–2.89) and mental illness (HR 1.80 95% CI 1.13–2.88) and further that there was an increased risk for short-term unemployment in the group on sick leave due to mental illness (HR1.57 95%CI 1.09–2.26).

Conclusions/Significance

Long-term sick leave increases the risks of both disability pension and unemployment even when taking health status into account. The results support the hypothesis that long-term sick leave may start a process of marginalization from the labor market.     

Is there a threshold size regulating seaward migration of brown trout and Atlantic salmon?

We investigated the influence of variation in body size and growth rate on age of smolting in Atlantic salmon and brown trout in four different Norwegian rivers. In Atlantic salmon smolt ages varied between 2 and 6 years, and in brown trout between 2 and 7 years. Smolt age was negatively correlated with parr growth, and positively correlated with smolt size. Age at smolting was more variable in the two northern than the two southern rivers. Smolt sizes and ages were also more variable in brown trout than in Atlantic salmon. Based on the observed variation in smolt size and age, we reject the hypothesis that a threshold size alone regulates age at smolting. Within populations smolt age depends on growth rate so that fast-growing parr smolted younger and smaller than slow-growing parr. We hypothesize that smolt size and age is a trade-off between expected benefits and costs imposed by differences in individual growth rate.