Effects of Long-Term Nitrogen Addition and Atmospheric Nitrogen Deposition on Carbon Accumulation in Picea sitchensis Plantations

This study aimed to assess the combined effects of long-term nitrogen (N) supply and nitrogen deposition (N _dep) on carbon (C) accumulation within Sitka spruce [Picea sitchensis (Bong.) Carr.] plantations in Scotland. Six study sites established from 1970 to 1982 were periodically N-fertilized, monitored over time and commonly surveyed in 2010. Soil, aboveground biomass, and ground vegetation C stock changes were analyzed; aboveground C stocks were correlated with total additional N experienced at each site, that is, the sum of experimental N supply (N _add) and site-specific accumulated N _dep from 1900 to 2010. Results showed a positive N effect on aboveground tree C stock and no decline in tree growth was observed either during fertilization or after the latest N addition. The amount of C in litter was significantly higher in experimentally N-treated plots, whereas the amount of C in understory vegetation was higher in control plots. Pooling all the compartments (that is, understory vegetation, litter, soil, and tree biomass) the total ecosystem C content was estimated for each site, and at most sites a higher C stock was estimated for N-treated plots. Differences in aboveground C accumulation rates between treated and control plots were lower at sites with high levels of accumulated N _dep. Our results indicate that site-specific accumulated N _dep should be considered to understand tree growth responses to N fertilization.     

Discovery of latitudinal gradient of triidothyronine concentrations in ectotherms as revealed from a cyprinid fish,the common roach Rutilus rutilus

Important life history traits in groups of ectotherms have been shown to vary along a latitudinal axis. Despite sustained interest to this phenomenon, the underlying physiological mechanisms of latitudinal adaptation remain poorly understood. Thyroid hormones (THs) are key regulators of metabolism, development, and growth, and are involved in shaping adult phenotypes in lower vertebrates, fishes and amphibians. We tested the hypothesis that concentrations of triiodothyronine (T₃), the most active form of THs, correlate with latitudinal gradient in ectotherms using a cyprinid fish, the common roach Rutilus rutilus as an example. Fish from seven locations between 46°45′ and 58°04′ N were studied for T₃ concentrations. Our results show a strong positive correlation between latitude and T₃ concentrations. There was a three-fold difference between the means of the extreme southern and northern samples. This is a first finding of latitudinal gradient of thyroid hormones in ectotherms. Photoperiodism and temperature were tested as main environmental factors influencing TH levels. In our results, the increase in T₃ concentrations along the south–north axis in ectotherms is, seemingly, associated with adaptation to differing thermal environments.     

A Review of Spatial Variation of Inorganic Nitrogen (N) Wet Deposition in China

Atmospheric nitrogen (N) deposition (N_dep), an important component of the global N cycle, has increased sharply in recent decades in China. Although there were already some studies on N_dep on a national scale, there were some gaps on the magnitude and the spatial patterns of N_dep. In this study, a national-scale N_dep pattern was constructed based on 139 published papers from 2003 to 2014 and the effects of precipitation (P), energy consumption (E) and N fertilizer use (F_N) on spatial patterns of N_dep were analyzed. The wet deposition flux of NH₄⁺-N, NO₃^--N and total N_dep was 6.83, 5.35 and 12.18 kg ha^-1 a^-1, respectively. N_dep exhibited a decreasing gradient from southeast to northwest of China. Through accuracy assessment of the spatial N_dep distribution and comparisons with other studies, the spatial N_dep distribution by Lu and Tian and this study both gained high accuracy. A strong exponential function was found between P and N_dep, F_N and N_dep and E and N_dep, and P and F_N had higher contribution than E on the spatial variation of N_dep. Fossil fuel combustion was the main contributor for NO₃^--N (86.0%) and biomass burning contributed 5.4% on the deposition of NO₃^--N. The ion of NH₄⁺ was mainly from agricultural activities (85.9%) and fossil fuel combustion (6.0%). Overall, N_dep in China might be considerably affected by the high emissions of NO_x and NH₃ from fossil fuel combustion and agricultural activities.     

Temperature and respiratory function in ectothermic vertebrates

Pulmonary ventilation is adjusted to maintain balance between O₂ demands and CO₂ elimination, which is essential for acid–base status in land ectothermic vertebrates. Rising temperatures cause increases in O₂ consumption (Q₁₀ effect) and decreases in the O₂ affinity of hemoglobin (a rightward shift in the oxygen–hemoglobin dissociation curve). These changes in air-breathing ectotherms are not proportional, i.e., the increased ventilation is relatively smaller than the change in metabolic rate. Therefore, the ratio between ventilation and metabolic rate is reduced, and consequently blood pH changes inversely with temperature. The combination of high temperatures and hypoxia exposure results in an amplified increase of ventilation, which may be explained by the balance between increased O₂-demand and decreased O₂-supply as well as increased O₂-chemoreceptors sensitivity. High temperature also increases pulmonary diffusing capacity. Global warming is expected to have significant impacts on the world’s climate, with temperature changes affecting living organisms, in relation to their physiology and distribution. These physiological mechanisms and their capacity to respond appropriately to temperature illustrate the complexity of the relationship between ambient temperature and the respiratory function in ectothermic vertebrates, which are particularly susceptible to change in their environment.     

Oxyconformers and oxyregulators: A quantitative index

Five empirical regression models for analysis of data on rate of oxygen uptake against oxygen level are compared.The quadratic polynomial model is the best in terms of providing a good statistical fit, in ease of computation and in providing model parameters of value when comparing and grouping species. Since the intercept parameter (B₀) characterizes only the position of the curve and since there was a strong negative correlation between the linear (B₁) and quadratic (B₂) parameters, the quadratic coefficient (B₂) alone is an informative index of the shape of the curve. B₂ not significantly different from zero implies oxyconformity, while B₂ significantly less than zero implies an appreciable degree of regulation.     

Metallobleomycins: electron spin resonance study on nitrosyl complex of iron(II)-Bleomycin

The ESR spectrum of the bleomycin-Fe(II)NO complex shows rhombic symmetry with a triplet hyperfine interaction in the g_z signal, and its ESR parameters have been compared with those of the ferrous-NO complexes of hemoproteins. The substitution of ₁₄NO by ₁₅NO gives the transition from a triplet to a doublet in the g_z absorption with a concomitant change in the nitrogen hyperfine constant. The addition of DNA to the ferrous-NO complex of bleomycin induces the greater separation of the g_x and g_y absorptions in comparison with the original ESR spectrum. The present three-line g_z signal for the bleomycin-Fe(II)-NO complex is indicative of weakened fifth axial nitrogen ligand-to-iron bonding with concomitantly stronger NO-to-iron bonding. On the other hand, the ESR feature of the bleomycin-Fe(III) complex is typical of the rhombic low-spin type, and no stable ferric-NO complex of bleomycin is formed.     

玉米农田空气动力学参数动态及其与影响因子的关系

对锦州玉米农田生态系统生长季内的粗糙度(z0)和零平面位移(d)动态特征及其与风速、株高(h)和叶面积指数(LAI)的关系分析表明:零平面位移(d)在玉米拔节后10d左右,株高约1.40m时开始出现,在抽雄前为0.80-1.00m,抽雄后为1.00-1.40m;z0在抽雄前小于0.20m,乳熟前后达到最大,约为0.40m.d/h和z0/分别为0.40-0.54和0.10-0.14,在h达到最大值前,分别随LAI增大而减小和增大.d出现前,z0与风速呈负指数关系,与LAI和h都呈线性关系.d出现后,风速与z0、d之和的关系比与各自的关系更显著;d与LAI、h都呈显著指数正相关关系,LAI、h对z0的影响大于d和z0 +d,且h的作用大于LAI.d出现至h达到最大期间,上述各种关系最为显著.研究结果可为建立空气动力学参数的动态参数化方案及改进陆面过程模型提供依据.     

Depilated (dep), a Mutant Gene That Affects the Coat of the Mouse and Acts in the Epidermis

Depilated is a recessive mutation on Chromosome 4 in the position b^-1.93±0.51^- dep^-3.45±0.68.^-Pt. It causes severe abnormalities of hair structure. The site of action of dep was investigated by the method of dermal-epidermal recombination. Skins from 14-day mutant and normal mouse embryos were separated into dermal and epidermal components, recombined, and grown in histocompatible mouse testes for 20 days. The recombinations made were +/+ epidermis with +/+ dermis, +/+ epidermis with dep/dep dermis, dep/dep epidermis with +/+ dermis and dep/dep epidermis with dep/dep dermis. Grafts that contained mutant epidermis as one of the components produced hairs that were similar to those found in depilated mice. There was no observable effect of the dermis on hair types produced in this experiment.     

Use of operative temperature and standard operative temperature models in thermal biology

Operative temperature (T_e) and standard operative temperature (T_es) models have been used to address ecological questions about the thermal biology of ectotherms and endotherms for over 25 years. This review focuses on the accuracy and use of T_e and T_es models in ecological and physiological studies. The utility of T_e and T_es models lie in the fact that they take a multivariate problem involving inputs of air temperature, ground temperature, solar radiation, and wind speed and map them into a single thermal metric on a spatial scale appropriate for the animal. The most reliable T_e models are copper casts that mimic the morphology and absorptivity of an animal. Simplified T_e models such as cylinders and spheres have been shown to produce errors in T_e as large as 12 °C under certain conditions and should only be used after careful calibration against a live animal. The accuracy of heated T_es models has been addressed in much less detail then that of T_e models. When calibrated and used under conditions of low solar radiation, heated taxidermic mounts and simplified T_es models produce errors in net heat production on the order of 5% or less. In order to provide reliable data, all types of models must be calibrated over an ecologically realistic range of environmental conditions experienced by the animal. This advice has been largely ignored in the literature, where 61% of the of studies examined failed to properly calibrate the models prior to use. Additionally, studies using these models tend to lack experimental rigor, using only one or two models to make measurements on 1 or 2 days of the active season. When used correctly, T_e and T_es models can be powerful tools for integrating the thermal environment experienced by an animal into a single metric that can address questions regarding the ecology, physiology, and behavior of endotherms and ectotherms. However, until investigators make the effort to use these models in a scientifically valid manner with proper calibration and experimental design their value to thermal biologists will be limited.     

A Class of Pairwise Models for Epidemic Dynamics on Weighted Networks

In this paper, we study the SIS (susceptible–infected–susceptible) and SIR (susceptible–infected–removed) epidemic models on undirected, weighted networks by deriving pairwise-type approximate models coupled with individual-based network simulation. Two different types of theoretical/synthetic weighted network models are considered. Both start from non-weighted networks with fixed topology followed by the allocation of link weights in either (i) random or (ii) fixed/deterministic way. The pairwise models are formulated for a general discrete distribution of weights, and these models are then used in conjunction with stochastic network simulations to evaluate the impact of different weight distributions on epidemic thresholds and dynamics in general. For the SIR model, the basic reproductive ratio R ₀ is computed, and we show that (i) for both network models R ₀ is maximised if all weights are equal, and (ii) when the two models are ‘equally-matched’, the networks with a random weight distribution give rise to a higher R ₀ value. The models with different weight distributions are also used to explore the agreement between the pairwise and simulation models for different parameter combinations.     

Could the intrinsic rate of increase represent the fitness in terrestrial ectotherms?

The intrinsic rate of increase (r_m) has been considered as an important indicator of fitness in terrestrial ectotherms since long. It is actually an equivalent to the instantaneous growth rate of the exponential equation for describing the density-independent population growth. In terrestrial ectotherms, r_m has been demonstrated to be temperature-dependent. The temperature at which r_m was maximal, was considered to be the “optimal” temperature for fitness in Amarasekare and Savage (2012), but this definition needs further analysis. Only r_m cannot provide thorough representation of fitness. Because body size can affect the competitive abilities in many terrestrial ectotherms, both population size and body size should be considered in measuring the fitness of ectotherms. The rule of “bigger is better” requires relatively low temperature to increase in body size, whereas relatively high temperature is required for a rapid increase in population size. Thus, there is presumably a trade-off in temperature for adjusting individual body size and population size to achieve maximum fitness. We hypothesized that this temperature could be reflected by the intrinsic optimum temperature for developmental rate in the Sharpe–Schoolfield–Ikemoto model, and it led to a temperature estimate around 20 °C. However, the traditional viewpoint based on the temperature corresponding to the maximal intrinsic rate of increase provides a temperature estimate around 30 °C. This study suggests that a low temperature around 20 °C might authentically represent the optimal ambient temperature for fitness in terrestrial ectotherms. It implies that thermal biologists who are interested in the effect of temperature on the fitness in terrestrial ectotherms should pay more attention to their performance at low temperature rather than high temperature.     

Nitrogen deposition and greenhouse gas emissions from grasslands: uncertainties and future directions

Increases in atmospheric nitrogen deposition (N_dep) can strongly affect the greenhouse gas (GHG; CO₂, CH₄, and N₂O) sink capacity of grasslands as well as other terrestrial ecosystems. Robust predictions of the net GHG sink strength of grasslands depend on how experimental N loads compare to projected N_dep rates, and how accurately the relationship between GHG fluxes and N_dep is characterized. A literature review revealed that the vast majority of experimental N loads were higher than levels these ecosystems are predicted to experience in the future. Using a process‐based biogeochemical model, we predicted that low levels of N_dep either enhanced or reduced the net GHG sink strength of most grasslands, but as experimental N loads continued to increase, grasslands transitioned to a N saturation‐decline stage, where the sensitivity of GHG exchange to further increases in N_dep declined. Most published studies represented treatments well into the N saturation‐decline stage. Our model results predict that the responses of GHG fluxes to N are highly nonlinear and that the N saturation thresholds for GHGs varied greatly among grasslands and with fire management. We predict that during the 21st century some grasslands will be in the N limitation stage where others will transition into the N saturation‐decline stage. The linear relationship between GHG sink strength and N load assumed by most studies can overestimate or underestimate predictions of the net GHG sink strength of grasslands depending on their N baseline status. The next generation of global change experiments should be designed at multiple N loads consistent with future N_dep rates to improve our empirical understanding and predictive ability.     

Hydrolytic Enzyme Production is Associated with Candida Albicans Biofilm Formation from Patients with Type 1 Diabetes

Oral candidosis is common in patients with diabetes mellitus, as yeasts, particularly Candida albicans, have the propensity to colonise, form biofilms and release hydrolytic enzymes which cause inflammation. This study aimed to investigate these characteristics in isolates from three groups of patients with type 1 diabetes: individuals with better controlled diabetes (BCD; ≥6 <8%), individuals with poorly controlled diabetes (PCD; ≥8%) and non-diabetics (ND; HbA_1c <5.9%). The biomass (Bm), phospholipase (P_z), haemolysin (H_z) and proteinase (Pr_z) were assessed using a microtitre biofilm assay and agar-based hydrolytic enzyme assays. Biofilm formation was significantly increased in the PCD group compared to ND and BCD groups (P < 0.05). No significant differences in P_z levels were observed between groups, whereas both H_z and Pr_z were significantly greater in the diabetes groups than in the healthy control group (P < 0.05). Statistically significant correlations were found to exist between the HbA_1c levels of the patients and the Bm (R = 0.384; P = 0.033), haemolysin activity (R = ?0.455; P = 0.010) and proteinase activity (R =  ?0.531; P = 0.002). There was no apparent correlation between the Bm and P_z activity (R = ?0.305; P = 0.053) or H_z activity (R = ?0.100; P = 0.296). However, a negative correlation was found between Bm and Pr_z values (R = ?0.343; P = 0.030). These data suggest that biofilm formation is likely to play a role in the pathogenicity of oral candidosis, and in patients with diabetes, this may be due to the ability of C. albicans to adapt to the altered physiological environment. The production of hydrolytic enzymes is independently associated with this growth modality.     

Molecular Evidence on the Evolutionary and Biogeographical Patterns of European Cyprinids

The phylogenetic relationships of 106 European cyprinid taxa were determined based on the complete nucleotide sequence (1140 bp) of the mitochondrial cytochrome b gene. The molecular phylogeny was used (1) to revise the current systematics of European cyprinids, (2) to establish the phylogenetic utility of traditional morphological characters that are widely used in Cyprinidae systematics, and (3) to discuss alternative hypotheses on the biogeography of the family in Europe. The age of the major lineages within European cyprinids was tentatively estimated with a molecular clock and showed full agreement with the fossil record of the group. Moreover, the results provided unambiguous evidence for a close phylogenetic affinity of some Caucasian and Greek endemic cyprinid taxa (e.g., B. capito and B. brachycephalus and Leuciscus keadicus, Barbus graecus, and B. albanicus, respectively) to Iberian and North African, but not Central European, cyprinids. The existence of such unexpected phylogenetic relationships refutes the classical hypothesis on the biogeography of European cyprinids, which assumes a dispersal of the cyprinid fauna from central Europe to southern Europe and northern Africa during the Miocene (and, hence, predicts a close phylogenetic relationship of all Caucasian, Greek, Iberian, and North African cyprinids to central European taxa). Instead, the existence of a Mediterranean realm independent of the central European route seems plausible based on the molecular evidence. It is likely that the new biogeographical scenario proposed here might apply to other primary freshwater European animals with low dispersal abilities, including fish, amphibians, and invertebrates. Received: 2 February 1999 / Accepted: 16 March 1999     

Water deprivation drives intraspecific variability in lizard heat tolerance

Quantifying intraspecific variation in heat tolerance is critical to understand how species respond to climate change. In a previous study, we recorded variability in critical thermal maxima (CT_max) by 3 °C among populations of small Iberian lizard species, which could substantially influence predictions of climate-driven activity restriction. Here, we undertake experiments to examine whether we could reproduce similar levels of heat-tolerance variability in response to water deficit. We hypothesized that deprivation of drinking water should increase variability in CT_max between populations more than deprivation of food under the theoretical expectation that the variation of the more limiting resource must trigger stronger variation in physiological performance. We measured CT_max after manipulating availability of live prey and drinking water in two populations of an arid and a mesic lizard species from the Iberian Peninsula. We quantified a mean CT_max across all studied lizards of 44.2 °C ± 0.2 SE for the arid species and 41.7 °C ± 0.3 SE for the mesic species. Using multimodel inference, we found that water deprivation (combined with food supply) caused population differences in CT_max by 3 to 4 °C which were two to three times wider than population differences due to food deprivation (combined with water supply) or to food and water provision. To highlight the need for more thermo-hydroregulatory research, we examined bias in research effort towards thermal versus hydric environmental effects on heat tolerance through a systematic literature review. We show that environmental temperature has been used five times more frequently than precipitation in ecological studies of heat tolerance of terrestrial species. Studies linking thermal tolerance of ectotherms to the interplay of air temperature and water availability are needed in the face of projected increases in aridity and drought in the 21st century, because the balance of body temperature and water resources are functionally interlinked.     

The thermoregulatory strategy of two sympatric colubrid snakes affects their demography

Population dynamics of terrestrial vertebrates are affected by climatic fluctuations, notably in ectotherms. An understanding of the interaction between physiology and demographic processes is necessary to predict the impacts of climate change. Reptiles are particularly sensitive to temperature, but only a few studies have explored the relationship between thermoregulatory strategy and demography in these animals. Using 12 years of mark-recapture data on two sympatric colubrid snakes (Hierophis viridiflavus and Zamenis longissimus), we tested whether demographic parameters are influenced by contrasted thermoregulatory strategies. The thermophilic and conspicuous species (H. viridiflavus) grew faster than the thermoconforming and secretive species (Z. longissimus), and this difference was most pronounced in open habitats, suggesting that the metabolic benefits associated with high thermal preferences depend on environmental factors at small spatial scales. Survival varied annually in both species, but was not lower in H. viridiflavus despite a higher degree of exposure. In Z. longissimus, survival was negatively affected by low temperatures during the active season, possibly underlying an exposure trade-off.     

Correcting Estimators of θ and Tajima's D for Ascertainment Biases Caused by the Single-Nucleotide Polymorphism Discovery Process

Most single-nucleotide polymorphism (SNP) data suffer from an ascertainment bias caused by the process of SNP discovery followed by SNP genotyping. The final genotyped data are biased toward an excess of common alleles compared to directly sequenced data, making standard genetic methods of analysis inapplicable to this type of data. We here derive corrected estimators of the fundamental population genetic parameter θ = 4N_eμ (N_e, effective population size; μ, mutation rate) on the basis of the average number of pairwise differences and on the basis of the number of segregating sites. We also derive the variances and covariances of these estimators and provide a corrected version of Tajima's D statistic. We reanalyze a human genomewide SNP data set and find substantial differences in the results with or without ascertainment bias correction.     

The reproductive period of tarantulas is constrained by their thermal preferences (Araneae,Theraphosidae)

Locomotor and physiological performance of ectotherms are affected by temperature. Thermoregulation is achieved by changes in behavior and the selection of micro-habitats with adequate temperatures to maintain the body temperature (T_b) within a range of preference. Apart from this temperature dependence at spatial scales, ectotherms are also affected by temperature at temporal scale. For instance, ectotherms can only be active some months of the year, particularly in temperate environments. Tarantulas are ectotherms that live in burrows most of their life. Nevertheless, after the sexual maturation molt, males leave their refugia and start a wandering life searching for females to mate. The reproductive period varies among species. In some species walking males are seen in late spring or early summer, while in other species males are only seen during fall or winter. Apart from the differences in lifestyles after maturation, tarantulas exhibit sexual dimorphisms in longevity and body mass, having smaller, shorter-lived males. Thus, to optimize energetic budgets, decreasing thermoregulation costs, we hypothesize and examine a putative correlation between an individual's preferred body temperature (T_pref) and the environmental temperature during the reproductive period. Hence, we characterize T_pref in seven tarantula species and analyze which factors (i.e., time of day, body mass, and sex) correlated with it. Furthermore, we assess putative correlated evolution of T_pref with ambient temperature (minima, mean, and maxima) during the reproductive period by means of phylogenetic independent contrasts. We did not find differences in thermal preferences between sexes; and only one species, Acanthoscurria suina, exhibited diel differences in T_pref. We found evidence of correlated evolution between T_pref and minimum temperature during the reproductive period among all seven species studied herein. Our results show that the reproductive period is constrained by thermal preferences, dictating when males can start their wandering life to mate.     

Crystal Structure of the Electron Carrier Domain of the Reaction Center Cytochrome cz Subunit from Green Photosynthetic Bacterium Chlorobium tepidum

In green sulfur photosynthetic bacteria, the cytochrome c_z (cyt c_z) subunit in the reaction center complex mediates electron transfer mainly from menaquinol/cytochrome c oxidoreductase to the special pair (P840) of the reaction center. The cyt c_z subunit consists of an N-terminal transmembrane domain and a C-terminal soluble domain that binds a single heme group. The periplasmic soluble domain has been proposed to be highly mobile and to fluctuate between oxidoreductase and P840 during photosynthetic electron transfer. We have determined the crystal structure of the oxidized form of the C-terminal functional domain of the cyt c_z subunit (C-cyt c_z) from thermophilic green sulfur bacterium Chlorobium tepidum at 1.3-Å resolution. The overall fold of C-cyt c_z consists of four α-helices and is similar to that of class I cytochrome c proteins despite the low similarity in their amino acid sequences. The N-terminal structure of C-cyt c_z supports the swinging mechanism previously proposed in relation with electron transfer, and the surface properties provide useful information on possible interaction sites with its electron transfer partners. Several characteristic features are observed for the heme environment: These include orientation of the axial ligands with respect to the heme plane, surface-exposed area of the heme, positions of water molecules, and hydrogen-bond network involving heme propionate groups. These structural features are essential for elucidating the mechanism for regulating the redox state of cyt c_z.