西印度洋地区海草生态系统

海草是海洋被子植物,广泛分布在温带和热带的海岸带水域,是地球上水生生态系统中最具生产力的生物之一.     

雄性波罗的海灰海豹(Halichoerus grypus)骨组织的矿物密度

本文利用非侵入计算层析X射线摄影法(pQCT)研究了雄性波罗的海灰海豹(4～23岁龄)骨组织的矿物密度(mg/cm3).资料按照收集的年份分组.A组1850～1955年,有机氯(OCs)大量引入之前的时期;B组1965～1985年,OC污染十分严重的时期;C组1986～1997年,OCs浓度逐渐减小的时期.测量结果的复现性良好,变异系数(CV)为0.1%～2.1%.1986～1997年收集的标本中桡骨小梁的矿物密度比1965～1985年收集的标本的明显要高(p＜0.05).1986～1997年收集的标本中,下颌骨的皮层骨矿物密度明显地低于1850～1955年收集的标本(p＜0.05).这些结果表明小梁和皮层骨在一段时间内的不同响应.在OC污染非常严重的时期(1965～1985年),小梁骨矿物密度最低,而在1985～1997年收集的标本中,皮层骨密度最低,该时段是一个OC污染程度相当低的时期.有关这些效应背后的机制目前尚不知道.但是,可以假定这里涉及到OCs.由于目前缺乏有关研究个体中OCs残留水平的资料,因此不可能评估OCs在这方面的影响.     

Rival recognition affects male contest behavior in sand lizards (Lacerta agilis)

Individual male sand lizards meet repeatedly during mate search and engage in costly interactions. If males can recognize rivals, the number of costly fights with a predictable outcome may be reduced. In staged contests between males, second interactions are on average significantly shorter than first ones, suggesting individual recognition. When aggressive behavior differs substantially between the sexes, the more aggressive sex may be predicted to have more variation in skin traits located on the parts of the body displayed during contests; this would facilitate individual recognition. Male (aggressive) sand lizards are more variable in two of three lateral skin traits displayed during males' contests, while females (non-aggressive) are more variable in one dorsal skin trait; in four other dorsal traits there was no difference in variability between the sexes.     

Buffer sensitivity of photosynthetic carbon utilisation in eight tropical seagrasses

Some of the mechanisms involved in inorganic carbon (Ci) acquisition by tropical seagrasses from the western Indian Ocean were described by Björk et al. (Mar Biol 129:363–366, 1997). However, since then, it has been found that an additional, buffer-sensitive, system of Ci utilisation may operate in some temperate seagrasses (Hellblom et al. in Aquat Bot 69:55–62, 2001, Hellblom and Axelsson in Photos Res 77:173–191, 2003); this buffer sensitivity indicates a mechanism in which electrogenic H⁺ extrusion may form acidic diffusion boundary layers, in which either HCO ₃ ^? –H⁺ is co-transported into the cells, or where HCO ₃ ^? is converted to CO₂ (as catalysed by carbonic anhydrase) prior to uptake of the latter Ci form. Because a buffer was used in the 1997 study, we found it important to reinvestigate those same eight species, taking into account the direct effect of buffers on this potential mode of Ci acquisition in these plants. In doing so, it was found that all seagrass species investigated except Cymodocea serrulata were sensitive to 50 mM TRIS buffer of the same pH as the natural seawater in which they grew (pH 8.0). Especially sensitive were Halophila ovalis, Halodule wrightii and Cymodocea rotundata, which grow high up in the intertidal zone (only ca. 50–65% of the net photosynthetic activity remained after the buffer additions), followed by the submerged Enhalus acoroides and Syringodium isoetifolium (ca. 75% activity remaining), while Thalassia hemprichii and Thalassodendron ciliatum, which grow in-between the two zones, were less sensitive to buffer additions (ca. 80–85% activity remaining). In addition to buffer sensitivity, all species were also sensitive to acetazolamide (AZ, an inhibitor of extracellular carbonic anhydrase activity) such that ca. 45–80% (but 90% for H. ovalis) of the net photosynthetic activity remained after adding this inhibitor. Raising the pH to 8.8 (in the presence of AZ) drastically reduced net photosynthetic rates (0–14% remaining in all species); it is assumed that this reduction in rates was due to the decreased CO₂ concentration at the higher pH. These results indicate that part of the 1997 results for the same species were due to a buffer effect on net photosynthesis. Based on the present results, it is concluded that (1) photosynthetic Ci acquisition in six of the eight investigated species is based on carbonic anhydrase catalysed HCO ₃ ^? to CO₂ conversions within an acidified diffusion boundary layer, (2) C. serrulata appears to support its photosynthesis by extracellular carbonic anhydrase catalysed CO₂ formation from HCO ₃ ^? without the need for acidic zones, (3) H. ovalis features a system in which H⁺ extrusion may be followed by HCO ₃ ^? –H⁺ co-transport into the cells, and (4) direct, non-H⁺-mediated, uptake of HCO ₃ ^? is improbable for any of the species.     

Stress on and off the job as related to sex and occupational status in white-collar workers

Sixty healthy non-smoking white collar employees, aged 30–50, from a large corporation in Sweden participated in the study. There were four groups: 15 male and 15 female middle managers, 15 male and 15 female clerical workers. Each participant was examined individually with regard to cardiovascular and neuroendocrine functions and self-reports for 12 consecutive hours under each of two conditions: (1) a normal day at work (9 a.m.–5 p.m.) and after work (6–9 p.m.), and (2) for the same time period during work-free conditions at home. In addition, everyone was given a videotaped type A-interview and a general health check-up including blood-lipid determination. Attitudes towards work, total workload (including responsibilities outside the paid work) and sex role identity were examined by questionnaires. As expected, all groups showed a moderate increase in cardiovascular and neuroendocrine activity during the day at work. After work, however, interesting group differences emerged, suggesting slower unwinding in female managers. Differences related to occupational level and/ or sex were found for autonomy and social support at work, competitiveness, sex role and reported conflict between demands from paid work and other responsibilities. The stress profile of the female managers was considered in terms of possible long-term health risks.     

Process-diagnostic patterns of chlorobiphenyl congeners in two radiochronologically characterized sediment cores from the northern Baffin Bay.

Polychlorinated biphenyl (PCB) patterns were interpreted in two radioisotopically constrained sediment cores from the Arctic ocean in order to seek clues about their large-scale environmental fates. Low but clearly measurable fluxes of individual PCB congeners were observed in deeper layer sediments, corresponding to the past 170 years, in a single dated core from the Baffin Bay shelf. Fluxes of the dominant individual congeners in the surface sediments were 20-100 pg m(-2) d(-1). Combining these data with the sediment data from the Arctic Monitoring and Assessment Program, it appears that the PCB distribution in Arctic surface sediments is governed by the organic carbon (OC) content of the sediments. The historical development of the PCB congener fingerprint suggests that the modern sediments are enriched in medium-chlorinated congeners, implying that there are at least two significant, but distinctly different, sink processes acting on the PCB pool. The relative abundance of light-to-heavy congeners, in mid-shelf marine sediments of similar ages, between 40 degrees N and 76 degrees N latitude suggests a northward dilution of PCBs which is stronger attenuated for heavier congeners, consistent with a temperature-driven global fractionation process. The significant presence of PCB in historical archives pre-dating the organochlorine society, as observed in this and several previous studies, awaits a fuller explanation.     

Maximum species richness at intermediate frequencies of disturbance: consistency among levels of productivity

Development of a mechanistic understanding and predictions of patterns of biodiversity is a central theme in ecology. One of the most influential theories, the intermediate disturbance hypothesis (IDH), predicts maximum diversity at intermediate levels of disturbance frequency. The dynamic equilibrium model (DEM), an extension of the IDH, predicts that the level of productivity determines at what frequency of disturbance maximum diversity occurs. To test, and contrast, the predictions of these two models, a field experiment on marine hard-substratum assemblages was conducted with seven levels of disturbance frequency and three levels of nutrient availability. Consistent with the IDH, maximum diversity, measured as species richness, was observed at an intermediate frequency of disturbance. Despite documented effects on productivity, the relationship between disturbance and diversity was not altered by the nutrient treatments. Thus, in this system the DEM did not improve the understanding of patterns of diversity compared to the IDH. Furthermore, it is suggested that careful consideration of measurements and practical definitions of productivity in natural assemblages is necessary for a rigorous test of the DEM.     

Slope aspect modifies community responses to clear-cutting in boreal forests

Slope aspect modifies microclimate and influences ecological processes and spatial distribution of species across forest landscapes, but the impact of slope aspect on community responses to disturbance is poorly understood. Such insight is necessary to understand landscape community dynamics and resilience. We compared bryophyte (liverworts and mosses) communities in matched 0.02-ha plots of four boreal stand types in central Sweden: recently clear-felled and mature stands dominated by Norway spruce in south-facing and north-facing slopes. Differences between forests and clear-cuts were interpreted as effects of clear-cutting, and differences between south- and north-facing slopes as effects of aspect. In response to clear-cutting, bryophyte cover and composition changed more in south-facing slopes. Only one out of ten significantly declining species in south-facing slopes also declined significantly in north-facing slopes. North-facing slopes lost fewer bryophyte species, and among those, fewer forest species and fewer species associated with wood and bark. In north-facing slopes, the average proportions of mosses and liverworts shared between the forest and the clear-cut plot were 88% and 74%, respectively. Corresponding numbers for south-facing slopes were 79% and 33%. In addition, more bryophyte species were added in north- than south-facing slopes after clear-cutting, somewhat reducing the difference in compositional change between aspects. South- and north-facing mature forests differed in species composition, mostly due to higher richness of mosses in south-facing slopes. The smaller changes in bryophyte communities on north-facing slopes in response to clear-cutting have implications for ecosystem dynamics and management as high local survival may enhance landscape-level resilience.     

Global change shifts vegetation and plant-parasite interactions in a boreal mire

The aim of this study was to detect vegetation change and to examine trophic interactions in a Sphagnum-dominated mire in response to raised temperature and nitrogen (N) addition. A long-term global-change experiment was established in 1995, with monthly additions of N (30 kg x ha(-1) x yr(-1)) and sulfur (20 kg x ha(-1) x yr(-1)) during the vegetation period. Mean air temperature was raised by 3.6 degrees C with warming chambers. Vegetation responses were negligible for all treatments for the first four years, and no sulfur effect was seen during the course of the experiment. However, after eight years of continuous treatments, the closed Sphagnum carpet was drastically reduced from 100% in 1995 down to 41%, averaged over all N-treated plots. Over the same period, total vascular plant cover (of the graminoid Eriophorum vaginatum and the two dwarf-shrubs Andromeda polifolia and Vaccinium oxycoccos) increased from 24% to an average of 70% in the N plots. Nitrogen addition caused leaf N concentrations to rise in the two dwarf-shrubs, while for E. vaginatum, leaf N remained unchanged, indicating that the graminoid to a larger extent than the dwarf-shrubs allocated supplemented N to growth. Concurrent with foliar N accumulation of the two dwarf-shrubs, we observed increased disease incidences caused by parasitic fungi, with three species out of 16 showing a significant increase. Warming caused a significant decrease in occurrence of three parasitic fungal species. In general, decreased disease incidences were found in temperature treatments for A. polifolia and in plots without N addition for V. oxycoccos. The study demonstrates that both bryophytes and vascular plants at boreal mires, only receiving background levels of nitrogen of about 2 kg x ha(-1) x yr(-1), exhibit a time lag of more than five years in response to nitrogen and temperature rise, emphasizing the need for long-term experiments. Moreover, it shows that trophic interactions are likely to differ markedly in response to climate change and increased N deposition, and that these interactions might play an important role in controlling the change in mire vegetation composition, with implications for both carbon sequestration and methane emission.     

Trace element concentration in wheat grain: results from the Swedish long-term soil fertility experiments and national monitoring program

Concentrations of trace elements in wheat grain sampled between 1967 and 2003 from the Swedish long-term soil fertility experiments were analyzed using ICP-MS. The long-term effect of inorganic and organic fertilization on trace metal concentrations was investigated including the impact of atmospheric deposition and myccorhiza, whereas other factors such as soil conditions, crop cultivar, etc. are not discussed in this paper. Mean values derived from 10 experimental sites were reported. Significantly declining Pb and Cd concentrations in wheat grain could be explained by lower atmospheric deposition. Mean Se contents in all samples were 0.031 mg kg⁻¹ grain dry weight. No samples had sufficiently high Se concentrations for human (0.05 mg Se kg⁻¹) or animal demand (0.1 mg Se kg⁻¹). Concentrations of Co in wheat grain were extremely low, 0.002–0.005 mg Co kg⁻¹ grain dry weight, and far below the minimum levels required by animals, which applied to all fertilizer treatments. A doubling of Mo concentrations in grain since 1975 resulted in Cu/Mo ratios often below one, which may cause molybdenosis in ruminants. The increase in Mo concentrations in crops correlated with the decline in sulfur deposition. Concentrations of Cu and Fe declined in NPK-fertilized wheat as compared to unfertilized or manure-treated wheat. Very low concentrations of Se and Co and low concentrations of Fe and Cu require attention to counteract risks for deficiencies. The main characteristic of the study is that there are few significant changes over time between different fertilizer treatments, but throughout there are low concentrations of most trace elements in all treatments. In general, good agreement between concentrations in wheat from the long-term fertility experiments and the national monitoring program indicate that values are representative.