利用遥感信息研究西藏地区主要植被年内和年际变化规律

利用1982～2000年NOAA-AVHRR月合成NDVI遥感资料和相关气象台站数据对我国西藏地区的稀疏草地、浓密草地和Tebit森林等主要植被的变化进行了初探。利用月合成NDVI的多年平均值分析了植被指数年内季节性变化规律及其与气候因子的关系,利用多年月合成NDVI的标准差描述了NDVI年际间波动情况。结果表明,在西藏地区,浓密草地和Tebit森林的NDVI植被指数年内变化规律呈明显的季节性,而稀疏草地则不明显;在年际变化方面,浓密草地月合成NDVI值波动幅度最大,Tebit森林次之,稀疏草地最小,且波动幅度较大的月份集中在NDVI值较高的植被生长季节6～10月份。     

Prehistoric versus modern Baltic Sea cod fisheries: selectivity across the millennia

Combining Stone Age and modern data provides unique insights for management, extending beyond contemporary problems and shifting baselines. Using fish chronometric parts, we compared demographic characteristics of exploited cod populations from the Neolithic Period (4500 BP) to the modern highly exploited fishery in the central Baltic Sea. We found that Neolithic cod were larger (mean 56.4 cm, 95% confidence interval (CI)+/-0.9) than modern fish (weighted mean length in catch =49.5+/-0.2 cm in 1995, 48.2+/-0.2 cm in 2003), and older (mean ages=4.7+/-0.11, 3.1+/-0.02 and 3.6+/-0.02 years for Neolithic, 1995, and 2003 fisheries, respectively). Fishery-independent surveys in 1995 and 2003 show that mean sizes in the stock are 16-17 cm smaller than reflected in the fishery, and mean ages approximately 1-1.5 years younger. Modelled von Bertalanffy growth and back-calculated lengths indicated that Neolithic cod grew to smaller asymptotic lengths, but were larger at younger ages, implying rapid early growth. Very small Neolithic cod were absent and large individuals were rare as in modern times. This could be owing to selective harvests, the absence of small and large fish in the area or a combination. Comparing modern and prehistoric times, fishery selection is evident, but apparently not as great as in the North Atlantic proper.     

Faster or slower: has growth of eastern Baltic cod changed?

Recent environmental changes have influenced the ecology and biology of eastern Baltic cod. Declining somatic condition, maturation at smaller size and restricted size distribution of the population suggest that growth rates have decreased between the early 2000s and the 2010s. Extensive age estimation problems have until now precluded testing of this hypothesis. This study presents evidence for a decrease in somatic growth rate of Baltic cod. Temporal patterns of growth, condition and maturation were analysed based on two complementary analyses: length frequency mode progression derived from DATRAS bottom trawl survey data and known-age samples, where size at age was back-calculated from daily otolith growth patterns. In the known-age samples, growth was positively related to somatic condition at capture with maturity dependent differences. Immature individuals had experienced significantly lower growth and were in lower condition at capture than mature individuals. Growth rates in the known-age samples were estimated at 9.5, 7.8 and 5.7?cm per year for age classes 1, 2 and 3 respectively. Growth between age 2 and 3 decreased significantly from 8.8?cm in the 1997 year class to 7.6?cm in the 2010 year class. While the 2001 and 2004 known-age samples were representative for the population, the 2013 sample was biased towards individuals with a higher condition and growth. Complementary length frequency analysis following the length mode of fish from age 2 to age 3 confirmed growth estimates from the early 2000s, while suggesting a 37.5% lower growth in 2013 compared with 2005.     

镉胁迫对金银花生理生态特征的影响

采用水培试验方法,研究了不同浓度镉(Cd)(0、5、10、25和50 mg·L^-1) 胁迫条件下藤本植物金银花的生长和生理特性.结果表明: 与对照相比,Cd胁迫对金银花的生长未造成明显影响,在5～50 mg·L^-1 Cd处理下,其生物量无明显差异(P>0.05),在低浓度Cd(5 mg·L^-1)处理下生物量有所增加,叶、根生物量和总生物量分别增加了2.88%、2.33%和1.25%,说明金银花对Cd具有较强的抗性.在低浓度Cd胁迫下,植物各器官的含水量和可溶性蛋白含量均有所降低,而根系和叶片的丙二醛含量分别增加51.90%和23.07%,叶绿素和类胡萝卜素含量则增加15.87%和24.89%,超氧化物歧化酶活性也显著增强.随着Cd浓度的增高,金银花体内的叶绿素和类胡萝卜素含量,以及超氧化物歧化酶活性均有所降低.     

Seasonal and annual stem respiration of Scots pine trees under boreal conditions

BACKGROUND AND AIMS: Stem respiration of trees is a major, but poorly assessed component of the carbon balance of forests, and important for geo-chemistry. Measurements are required under naturally changing seasonal conditions in different years. Therefore, intra- and inter-annual carbon fluxes of stems in forests were measured continuously from April to November in three consecutive years. METHODS: Stem respiratory CO2 fluxes of 50-year-old Scots pine (Pinus sylvestris) trees were continuously measured with a CO2 analyser, and, concomitantly, stem circumference, stem and air temperature and other environmental factors and photosynthesis, were also measured automatically. KEY RESULTS: There were diurnal, seasonal and inter-annual changes in stem respiration, which peaked at 1600 h during the day and was highest in July. The temperature coefficient of stem respiration (Q10) was greater during the growing season than when growth was slow or had stopped, and more sensitive to temperature in the growing season. The annual Q10 remained relatively constant at about 2 over the three years, while respiration at a reference temperature of 15 degrees C (R15) was higher in the growing than in the non-growing season (1.09 compared with 0.78 micromol m(-2) stem surface s(-1)), but was similar between the years. Maintenance respiration was 76 %, 82 % and 80 % of the total respiration of 17.46, 17.26 and 19.35 mol m2 stem surface in 2001, 2002 and 2003, respectively. The annual total stem respiration of the stand per unit ground area was 75.97 gC m(-2) in 2001 and 74.28 gC m(-2) in 2002. CONCLUSIONS: Stem respiration is an important component in the annual carbon balance of a Scots pine stand, contributing 9 % to total carbon loss from the ecosystem and consuming about 8 % of the carbon of the ecosystem gross primary production. Stem (or air) temperature was the most important predictor of stem carbon flux. The magnitude of stem respiration is modified by photosynthesis and tree growth. Solar radiation indirectly affects stem respiration through its effect on photosynthesis.     

Climate and fishing steer ecosystem regeneration to uncertain economic futures

Overfishing of large predatory fish populations has resulted in lasting restructurings of entire marine food webs worldwide, with serious socio-economic consequences. Fortunately, some degraded ecosystems show signs of recovery. A key challenge for ecosystem management is to anticipate the degree to which recovery is possible. By applying a statistical food-web model, using the Baltic Sea as a case study, we show that under current temperature and salinity conditions, complete recovery of this heavily altered ecosystem will be impossible. Instead, the ecosystem regenerates towards a new ecological baseline. This new baseline is characterized by lower and more variable biomass of cod, the commercially most important fish stock in the Baltic Sea, even under very low exploitation pressure. Furthermore, a socio-economic assessment shows that this signal is amplified at the level of societal costs, owing to increased uncertainty in biomass and reduced consumer surplus. Specifically, the combined economic losses amount to approximately 120 million € per year, which equals half of today''s maximum economic yield for the Baltic cod fishery. Our analyses suggest that shifts in ecological and economic baselines can lead to higher economic uncertainty and costs for exploited ecosystems, in particular, under climate change.     

Ecological forecasting under climate change: the case of Baltic cod

Good decision making for fisheries and marine ecosystems requires a capacity to anticipate the consequences of management under different scenarios of climate change. The necessary ecological forecasting calls for ecosystem-based models capable of integrating multiple drivers across trophic levels and properly including uncertainty. The methodology presented here assesses the combined impacts of climate and fishing on marine food-web dynamics and provides estimates of the confidence envelope of the forecasts. It is applied to cod (Gadus morhua) in the Baltic Sea, which is vulnerable to climate-related decline in salinity owing to both direct and indirect effects (i.e. through species interactions) on early-life survival. A stochastic food web-model driven by regional climate scenarios is used to produce quantitative forecasts of cod dynamics in the twenty-first century. The forecasts show how exploitation would have to be adjusted in order to achieve sustainable management under different climate scenarios.     

Demonstration of beta-N-acetyl-D-glucosaminidase and beta-N-acetyl-D-hexosaminidase in Drosophila Kc-cells.

Kc-cells from Drosophila melanogaster, grown under serum-free conditions, produce two beta-hexosaminidases and secrete these enzymes into the medium. The two enzymes were separated by DEAE-exchange chromatography. According to their substrate specificities one enzyme is a beta-N-acetyl-D-glucosaminidase (E.C.3.2.1.30), the other one a beta-N-acetyl-D-hexosaminidase (E.C.3.2.1.52). The beta-N-acetyl-D-glucosaminidase is predominant in the medium, the beta-N-acetyl-D-hexosaminidase within the cells. The Km values for the substrates pNP-GlcNAc, pNP-GalNAc, and (GlcNAc)2 are 0.8, 16.73, and 1.67 mM for the beta-N-acetyl-D-glucosaminidase and 0.24, 0.44, and 0.2 mM for the beta-N-acetyl-D-hexosaminidase. Both enzymes are inhibited by the products and the beta-N-acetyl-D-glucosaminidase is also inhibited stereospecifically by the substrates pNP-GlcNAc and (GlcNAc)2. Both enzymes are inhibited in a partial competitive way by acetamidolactones, the Kis being as low as 0.1 microM.     

Variations of snow petrel breeding success in relation to sea-ice extent: detecting local response to large-scale processes?

Demographic parameters were estimated for snow petrels Pagodroma nivea nesting at the study colony of Reeve Hill near Casey station, Antarctica between 1984 and 2003. Average breeding success for the colony varied from 18.2% to 76.5%. Breeding effort, hatching and fledging success were subject to a high interannual variability. We examined the influence of regional sea-ice extent on the breeding performance of snow petrels at Reeve Hill. Fewer birds were breeding when sea-ice had been extensive during April–May. Overall breeding success and fledging success were improved during years with extensive sea-ice cover in winter. Successful breeding effort and breeding success were depressed when there was extensive sea-ice cover during January–February. Sea surface temperatures also correlated to snow petrel breeding performance parameters. Previous work showed that large-scale climatic events (ENSO, Antarctic circumpolar wave) and the related sea-ice cover around the Antarctic might affect the lower trophic levels of the marine environment and consequently food availability for snow petrels. A comparison with the long-term study conducted at Ile des Pétrels (Terre Adélie) suggests that despite similarities in the underlying biological processes that control snow petrel breeding performance, the nature of the correlation of large-scale environmental factors with breeding performance differs substantially between the two colonies, probably because of the confounding effects of other environmental factors acting at a local scale (local weather, nest quality), which also affect bird body condition.