Cell density, chemical composition and toxicity of Chrysochromulina polylepis (Haptophyta) in relation to different N:P supply ratios

The influence of different N:P supply ratios on cell accumulation, chemical composition and toxicity of the marine haptophyte Chrysochromulina polylepis was examined in semi-continuous cultures. A non-axenic strain of C. polylepis was exposed to five different N:P supply ratios (N:P = 1:1, 4:1, 16:1, 80:1 and 160:1, by atoms), in order to create a range of N- and P-limited conditions. The toxicity per cell in C. polylepis was determined on four occasions at steady state cell density using the haemolytic activity of the cells expressed as saponin nanoequivalents. Haemolytic activity was demonstrated in all treatments, and increased in the algae when cell growth was nutrient limited (N:P = 1:1, 4:1, 80:1 and 160:1), compared to cells grown under non-limiting conditions (N:P = 16:1). This occurred regardless of the growth-limiting nutrient (N or P) and became more pronounced as nutrient limitation increased. In P-limited cultures the haemolytic activity per cell increased linearly with the cellular N:P ratio, whereas the N-limited cultures showed an opposite trend. The haemolytic activity per cell showed an inverse relationship with both cellular N and cellular P content. Cells limited by P showed a higher haemolytic activity than cells limited by N. The results suggest that toxicity in C. polylepis is strongly influenced by the physiological state of the algae. This may partially explain the large variability previously observed in the toxicity of C. polylepis blooms. The potential ecological significance of our findings is also discussed. Received: 18 November 1998 / Accepted: 5 July 1999     

斯德哥尔摩群岛水质历史上的城市影响

从历史的角度看,斯德哥尔摩市居民人数的增长对周围湖泊和沿岸地区的水质产生了负面影响.自19世纪中叶以来,政府的治理和为改善水质所采取的措施一直在进行中.由于采样很少,而且使用了不同的参数和方法,因此很难根据首次化学和生物调查结果来评估与以后若干年相比较的19世纪的水况.但是,可以根据开始于20世纪初的浮游生物调查的结果对水质进行一次回顾性评价.在具有与整个20世纪相似温度条件的夏季对反映富营养状况的蓝藻Planktothrixagardhii的发生进行了调查.调查结果表明,从20世纪初到90年代初.在斯德哥尔摩群岛,富营养化条件可能一直占优势.20世纪的最后10年,水质似乎比l00年前要好.今天较好的水况很可能是在度水处理方面采取适当措施的结果.     

Early postnatal ozone exposure alters rat nodose and jugular sensory neuron development

Sensory neurons originating in nodose and jugular ganglia that innervate airway epithelium (airway neurons) play a role in inflammation observed following exposure to inhaled environmental irritants such as ozone (O₃). Airway neurons can mediate airway inflammation through the release of the neuropeptide substance P (SP). While susceptibility to airway irritants is increased in early life, the developmental dynamics of afferent airway neurons are not well characterized. The hypothesis of this study was that airway neuron number might increase with increasing age, and that an acute, early postnatal O₃ exposure might increase both the number of sensory airway neurons as well as the number SP-containing airway neurons. Studies using Fischer 344 rat pups were conducted to determine if age or acute O₃ exposure might alter airway neuron number. Airway neurons in nodose and jugular ganglia were retrogradely labeled, removed, dissociated, and counted by means of a novel technique employing flow cytometry. In Study 1, neuron counts were conducted on postnatal days (PD) 6, 10, 15, 21, and 28. Numbers of total and airway neurons increased significantly between PD6 and PD10, then generally stabilized. In Study 2, animals were exposed to O₃ (2?ppm) or filtered air (FA) on PD5 and neurons were counted on PD10, 15, 21, and 28. O₃-exposed animals displayed significantly less total neurons on PD21 than FA controls. This study shows that age-related changes in neuron number occur, and that an acute, early postnatal O₃ exposure significantly alters sensory neuron development.     

Hierarchical analysis of vegetation dynamics over 71 years: soil-rainfall interactions in a Chihuahuan Desert ecosystem

Proliferation of woody plants in grasslands and savannas is a persistent problem globally. This widely observed shift from grass to shrub dominance in rangelands worldwide has been heterogeneous in space and time largely due to cross-scale interactions among soils, climate, and land-use history. Our objective was to use a hierarchical framework to evaluate the relationship between spatial patterns in soil properties and long-term shrub dynamics in the northern Chihuahuan Desert of New Mexico, USA. To meet this objective, shrub patch dynamics from 1937 to 2008 were characterized at patch and landscape scales using historical imagery and a recent digital soils map. Effects of annual precipitation on patch dynamics on two soils revealed strong correlations between shrub growth on deep sandy soils and above-average rainfall years (r = 0.671, P = 0.034) and shrub colonization and below-average rainfall years on shallow sandy soils (r = 0.705, P = 0.023). Patch-level analysis of demographic patterns revealed significant differences between shrub patches on deep and shallow sandy soils during periods of above- and below-average rainfall. Both deep and shallow sandy soils exhibited low shrub cover in 1937 (1.0% +/- 2.3% and 0.3% +/- 1.3%, respectively [mean +/- SD]) and were characterized by colonization or appearance of new patches until 1960. However, different demographic responses to the cessation of severe drought on the two soils and increased frequency of wet years after 1960 have resulted in very different endpoints. In 2008 a shrubland occupied the deep sandy soils with cover at 19.8% +/- 9.1%, while a shrub-dominated grassland occurred on the shallow sandy soils with cover at 9.3% +/- 7.2%. Present-day shrub vegetation constitutes a shifting mosaic marked by the coexistence of patches at different stages of development. Management implications of this long-term multi-scale assessment of vegetation dynamics support the notion that soil properties may constrain grassland remediation. Such efforts on sandy soils should be focused on sites characterized by near-surface water-holding capacity, as those lacking available water-holding capacity in the shallow root zone pose challenges to grass recovery and survival.     

Stress reactions in computerized administrative work

Ninety-five white-collar workers employed by an insurance company using visual display units (VDU) connected by telecommunication to a central computer filled in a questionnaire concerning psychosocial stressors in connection with work at the VDU. Eleven persons with extensive and ten with no work at VDUs were also studied during regular work, during breakdown of machinery, and in their leisure time. Self-reports on mood and alertness were recorded along with blood pressure, heart rate, and excretion of adrenaline and noradrenaline. Results indicate that (1) stress and mental strain occurred in association with delayed response times in the computer system and unpredicted interruptions of system operation, (2) such a temporary interruption caused an increase of blood pressure and adrenaline excretion, (3) complaints of stress and strain were repotted mainly by data-entry staff, (4) data-entry groups displayed a higher level of physiological arousal during post-work hours than a control group, and (5) that a majority of those who worked continuously at a VOU reported physical discomfort within 1.5 hours. It is concluded that stress and strain in computerized work may be counteracted at the technological and the organizational level: by reducing the duration and frequency of breakdowns, by reducing response times in the system, and by eliminating pure data-entry tasks.     

Testicular histopathology in deer mice (Peromyscus maniculatus) following exposure to polychlorinated biphenyl

Adult deer mice testes were subjected to routine histopathology following exposure to Aroclor 1254 supplemented diet (5 ppm), for 30 days. Body and testicular weight revealed no statistical significance between the control and treated animals. From a histological standpoint the testes of the controls were similar to normal murids and other animals. In contrast, the testes from treated animals displayed seminiferous tubules with significant degenerative alterations. These alterations included fewer layers of seminiferous epithelium exaggerated intercellular spaces and appearance of pyknotic nuclei. Most tubules displayed subluminal nuclei that morphologically could be identified as part of spermatozoa heads and these usually lacked tails, indicating that the treatment interfered with spermiogenesis. Therefore, we concluded that Aroclor 1254 as an environmental contaminant is highly destructive to seminiferous tubules, and that these histological alterations undoubtedly are responsible for the depressed fertility in Peromyscus following chronic exposure to PCBs, that has been reported in the literature.     

Interactive effects of impression management and organizational politics on job performance

The purpose of this research was to explore the interactive effect of organizational politics and impression management on supervisor ratings of employee performance. We hypothesized that the negative relationship between organizational politics and supervisor‐rated performance is weaker among employees who are high in impression management than among those low in impression management. Data were collected from a matched sample of 112 white‐collar employees and their supervisors. Results indicated that the interaction of organizational politics and impression management explained a significant incremental amount of variance in supervisor ratings of employee performance. These findings demonstrated that the extent to which an individual engaged in impression management in a non‐political atmosphere may have been a key component to receiving favorable performance ratings. Copyright © 2004 John Wiley & Sons, Ltd.     

Attitudes towards the conservation of biological diversity—A case study in Kristianstad Municipality,Sweden

Human actions towards land, freshwater and oceans have already caused biodiversity to decline. This study aims to investigate attitudes towards the conservation of biological biodiversity among different groups in a Swedish city, Kristianstad. An inquiry including statements measuring attitudes towards the conservation of habitats, animals and plants, to the biological diversity within selected local areas, to global and national areas, and to societal issues, was replied to by 271 persons. Deciduous forests, birds and wild flowers were given highest priority. An area categorized as wetland including lakeshore meadows with a rich bird life was prioritized as most important for conservation while a forest area was chosen as best for recreation. The experts gave lower priority to arable land, urban parks, domestic animals, agricultural and garden plants and to conifer forests compared to the other groups. Knowledge about what people in general value as important could facilitate the future planning of nature areas in the city of Kristianstad.