Whole-canopy carbon gain as a result of selection on individual performance of ten genotypes of a clonal plant

Game theoretical models predict that plant competition for light leads to reduced productivity of vegetation stands through selection for traits that maximize carbon gains of individuals. Using empirical results from a 5-year competition experiment with 10 genotypes of the clonal plant Potentilla reptans, we tested this prediction by analyzing the effects of the existing leaf area values on the carbon gain of the different genotypes and the consequent whole canopy carbon gain. We focused on specific leaf area (SLA) due to its role in the trade-off between light capture area and photosynthetic capacity per unit area. By combining a canopy model based on measured leaf area and light profiles with a game theoretical approach, we analyzed how changes in the SLA affected genotypic and whole-stand carbon gain. This showed that all genotypes contributed to reduced stand productivity. The dominant genotype maximized its share of total carbon gain, resulting in lower than maximal absolute gain. Other genotypes did not maximize their share. Hypothetical mutants of the dominant genotype were not able to achieve a higher carbon gain. Conversely, in other genotypes, some mutations did result in increased carbon gain. Hence, genotypic differences in the ability to maximize performance may determine genotype frequency. It shows how genotypic selection may result in lower carbon gains of the whole vegetation, and of the individual genotypes it consists of, through similar mechanisms as those that lead to the tragedy of the commons.     

Sleep Apnea-Hypopnea Quantification by Cardiovascular Data Analysis

Sleep disorders are a major risk factor for cardiovascular diseases. Sleep apnea is the most common sleep disturbance and its detection relies on a polysomnography, i.e., a combination of several medical examinations performed during a monitored sleep night. In order to detect occurrences of sleep apnea without the need of combined recordings, we focus our efforts on extracting a quantifier related to the events of sleep apnea from a cardiovascular time series, namely systolic blood pressure (SBP). Physiologic time series are generally highly nonstationary and entrap the application of conventional tools that require a stationary condition. In our study, data nonstationarities are uncovered by a segmentation procedure which splits the signal into stationary patches, providing local quantities such as mean and variance of the SBP signal in each stationary patch, as well as its duration . We analysed the data of 26 apneic diagnosed individuals, divided into hypertensive and normotensive groups, and compared the results with those of a control group. From the segmentation procedure, we identified that the average duration , as well as the average variance , are correlated to the apnea-hypoapnea index (AHI), previously obtained by polysomnographic exams. Moreover, our results unveil an oscillatory pattern in apneic subjects, whose amplitude is also correlated with AHI. All these quantities allow to separate apneic individuals, with an accuracy of at least . Therefore, they provide alternative criteria to detect sleep apnea based on a single time series, the systolic blood pressure.     

Photosynthesis and respiration of a diatom biofilm cultured in a new gradient growth chamber

Abstract A diatom biofilm was grown in a chamber developed for culture of biofilms in chemical gradients. The diatoms grew on a polycarbonate membrane filter which separated a sterile reservoir, with added phosphate, from a reservoir without phosphate. Within 3 weeks of inoculation, a thick biofilm developed on the surface of the filter. The biofilms were homogeneous and therefore suitable for calculations of O₂ diffusion fluxes from concentration profiles of O₂. Profiles of O₂, pH, and gross photosynthesis at different light intensities and liquid medium concentrations of dissolved inorganic carbon and O₂ were measured with microelectrodes. Respiratory activity in a layer of the biofilm was determined as the difference between gross photosynthesis and outflux of O₂ from that layer. The photosynthetic activity in a well-developed biofilm grown at 360 μEinst m⁻² s⁻¹ and 2.4 mM HCO₃⁻ was limited by the supply of inorganic carbon. Exposure to light above 360 μEinst m⁻² s⁻¹ stimulated gross photosynthesis as well as respiratory processes without affecting net outflux of O₂. Higher concentrations of inorganic carbon, on the other hand, enhanced gross photosynthesis without concurrent increase in respiratory rate, resulting in an increased outflux of O₂. High concentrations of O₂ in the liquid medium decreased the net outflux of O₂ with little effect on the gross photosynthesis. The effects of inorganic carbon and O₂ on the metabolic activities of the biofilm were consistent with the presence of photorespiratory activity.     

Kinetics of phosphate limited algal growth

The kinetics of phosphate limited growth of two green algae Chorella pyrenoidosa and Selenastrum capricornutum have been studied in chemostats. Several kinetic models which express the specific growth rate as a function of the intracellular phosphours content have been examined, and one of the models was found to be significantly better than the other models. The principles of this model were described in a recent paper by Nyholm. The kinetics of phosphate uptake have been investigated by adding pulses of phosphate to the chemostats. The uptake by phosphours deficient cells could be described by Michaelis–Menten kinetics for phosphate concentrations below approximately 500 μg P/liter. Further, with the assumption of a discontinuous adjustment of the uptake rate at the onset of phosphours deficiency, a complete kinetic model for growth and phosphate removal is proposed. The mean cell size and the contents of chlorophyll and RNA per unit dry weight have been measured for C. pyrenoidosa as a function of the dilution rate.     

A transport kinetic concept for ion uptake by plants

Summary A previously presented transport kinetic model for ion uptake by plants was tested by using data for copper uptake by barley grown in soil or water culture and corresponding data for copper concentration in the soil solution or culture solution. As no significant differences were obtained between experimentally determined values for copper uptake and those calculated by using the model, it was concluded that the experimental evidence was consistent with the proposed transport kinetic model. The model allows the Michaelis-Menten Constant of ion uptake and the Mean Maximal Rate of ion uptake to be calculated for various time intervals of the growth period of plants. The Michaelis-Menten Constant for copper uptake by barley grown in soil was the same as that for plants grown in water culture, provided that the soil solution and the water culture solution had the same chemical composition. The concentration of copper in the soil solution, at which the rate of copper uptake was zero, was 2–4 times larger than corresponding values obtained in water culture solution. re]19751028     

Dynamics of phosphate limited algal growth: Simulation of phosphate shocks

A simulation model is suggested which describes transient growth of the green alga Chlorella pyrenoidosa after exposure of phosphate limited chemostatic cultures to phosphate shocks. The specific growth rate is related to an internal concentration of functional phosphorus. The model includes a metabolic activity functional as suggested by Powell (1969), and it is assumed that phosphate taken up by the cells passes through an intermediate pool of not functional phosphorus which is thought to inhibit growth. Comparisons are made with a simpler model described previously.     

Molecular basis of prostaglandin potency. II. Proton NMR studies of the conformation of prostaglandin F2α

The proton nmr of PGF₂α (dissolved in aqueous tBuOH) in the presence of PrCl₃ and limited amounts of base shows LIS shifts for the terminal methyl indicating an average effective chain length (C-1 to C-20) like that of octanoic acid, further evidence that the α and ω carbons of prostaglandins are closer in space than would be expected based on a random distribution of conformers with alternate zig-zag sections of hydrocarbon chains. Assessing the exact nature of the sidechain alignment will require further experiments.     

Organization and expression of mouse Hox3 cluster genes

Summary The three yolk protein genes (yp) of Drosophila melanogaster are transcribed in a sex- and tissue-limited fashion. We have searched for cis-regulatory sequences in regions flanking yp1 and yp2 to identify the elements that confer female-specific expression in the fat body. One such 127 by element has previously been identified in this region. We show here the existence of two additional regions which confer female fat body-specific expression on an Adh reporter gene and on the native yp2 gene, respectively. This suggests some redundancy in the regulation of expression of the yp genes. Computer searches for putative binding sites for the DSX protein, which regulates sex-specific expression of the yp genes, revealed several such sites in our constructs. However, the significance of these is unclear since many such sites also occur in genes which one would not expect to be regulated in a sex-specific manner (e.g. Adh, Actin 5C). We suggest that DSX acts in concert with other proteins to mediate sex- and tissue-specific expression of the yp genes.     

Underestimation of Risk Due to Exposure Misclassification

Aim. Exposure misclassification constitutes a major obstacle when developing dose-response relationships for risk assessment. A non-differentional error results in underestimation of the risk. If the degree of misclassification is known, adjustment may be achieved by sensitivity analysis. The purpose of this study was to examine the full magnitude of measurement error in determining the prenatal exposure to methylmercury. Materials and methods. We used data from a prospective study of a Faroese birth cohort. Two biomarkers of methylmercury exposure were available, i.e., the mercury concentrations in cord blood and in maternal hair (sampled at the time of parturition). The laboratory imprecision on both chemical analyses was thought to be below 5% (coefficient of variation, CV). As a third exposure parameter, we used the dietary questionnaire response on frequency of whale meat dinners. Factor analysis and structural equation analysis were applied to assess the full extent of the imprecision. Results. The calculated total imprecision much exceeded the known laboratory variation: the CV was 28–30% for the cord-blood concentration and 52–55% for the maternal hair concentration. The dietary questionnaire response was even more imprecise. Conclusions. These findings illustrate that measurement error may be greatly underestimated if judged solely from reproducibility or laboratory quality data. Adjustment by sensitivity analysis is meaningful only if realistic measurement errors are applied. When exposure measurement errors are overlooked or underestimated, decisions based on the precautionary principle will not appropriately reflect the degree of precaution that was intended.