降雪对荒漠生物土壤结皮光合生理特性的影响

生物土壤结皮（BSC）广泛分布在干旱、半干旱区,对荒漠生态系统的稳定、平衡等具有重要意义。初步探讨了降雪量对腾格里沙漠东南缘藻类、地衣和藓类结皮叶绿素荧光参数、光合色素、丙二醛（MDA）及可溶性蛋白含量的影响。结果表明：结皮光合生理特性对降雪量的响应有显著差异。适量降雪激发3种结皮PSⅡ反应中心,引起光合色素、可溶性蛋白合成升高,MDA含量降低;过量降雪导致藻类和地衣结皮光合电子传递受阻,光合色素、可溶性蛋白合成减少,MDA含量升高,产生光抑制现象。适量冬季降雪对结皮具有一定的促进作用,而藓类结皮更能适应极端降雪环境,但相关分子机制还需深入研究。     

The Use of Pigment Signatures to Assess Phytoplankton Assemblage Structure in Estuarine Waters

The seasonal dynamics of chlorophyll a and the main accessory pigments accompanied by microscopic observations on live and fixed material were investigated in the Urdaibai estuary, Spain. Fucoxanthin was the dominant pigment during the peak in chlorophyll a, with which it was strongly correlated. Concentrations of fucoxanthin (81·30 μg l⁻¹) in the upper estuary were amongst the highest found in the literature, and were mainly associated with diatoms and symbiotic dinoflagellates. In the lower estuary, fucoxanthin showed values typical of coastal waters (<5 μg l⁻¹) and was mainly due to diatoms and prymnesiophytes. Chlorophyllb concentration was high along the estuary, followed the same seasonal pattern as chlorophyll a, and was associated with the presence of euglenophytes, chlorophytes and prasinophytes. High values of 19′-butanoyloxyfucoxanthin were often measured, but no organisms containing this pigment were observed in live or fixed samples. Alloxanthin and peridinin were found in low concentrations which was in agreement with cell counts of cryptophytes and peridinin-containing dinoflagellates. Two main patterns of phytoplankton assemblages were observed along the estuary. In the upper segments, during the chlorophylla maximum fucoxanthin containing algae masked the other algal groups, which were relatively more abundant during or after enhanced river flows. In the lower estuary, although dominated by fucoxanthin-containing algae, the other algal groups were important all year around. In this study, the use of diagnostic pigments has provided considerable insight into the temporal and spatial dynamics of phytoplankton assemblages by detecting phytoplankton taxa generally underestimated or overlooked by microscopy.     

Stratigraphy of fossil pigments and Cladophora and its relationship with deposition of tephra in Lake Mývatn,Iceland

Fossil plant pigments and Cladophora fragments were analyzed in a 6.53 m long sediment profile from Lake Mývatn, Iceland, covering most of its history of about 2300 years. A decrease in myxoxanthophyll (produced by Cyanobacteria) with time and an increase in the benthic Cladophora reflects a gradual shift from planktonic to benthic primary production as water depth is reduced (to 3.15 m at the core site) because of sediment accumulation.Two periods of relatively high concentrations of myxoxanthophyll coincided with relatively frequent deposition of tephra (volcanic ash) but did neither conform with tectonic activity which might have changed the water level nor the available climatic record. Sediment depth, tephra content and percent undegraded chlorophyll (an indicator of pigment preservation) together could explain 56.7% of the variation in myxoxanthophyll. It is hypothesized that temporary increases in myxoxanthophyll resulted from periodic nutrient enrichment by fresh tephra deposited in the watershed or because tephra increased the erosion of organic soil in the water catchment area.Fluctuations in Cladophora show an inverse relationship with myxoxanthophyll in the uppermost 4 m of the core, and may result from a shading effect of planktonic Cyanobacteria on the phytobenthos or competition for nutrients released by the bottom sediments.     

黄东海海区浮游植物色素吸收系数与叶绿素a浓度关系研究

浮游植物色素吸收与叶绿素a浓度关系研究是水色遥感生物-光学算法开发的重要组成部分,我们利用HD200304航次和HD200309航次的测量数据,开发了色素吸收系数的波段关系模型(αφ(λ)-αφ(675))和色素吸收系数与叶绿素a浓度关系(αφ(λ)-αφ(675))模型,并在模型开发的基础上,利用叶绿素a浓度反演典型波段的色素吸收系数,效果良好。     

Multi-proxy Reconstruction of Trophic State,Hypolimnetic Anoxia and Phototrophic Sulphur Bacteria Abundance in a Dimictic Lake in Northern Germany over the past 80 Years

During monthly investigations from 1996 to 2000, a hypolimnetic layer of phototrophic sulphur bacteria (Chromatium spp.) were observed in Lake Dudinghausen, a small dimictic lake in northern Germany. This paleolimnological study was initiated to detect if the occurrence of sulphur bacteria was related to cultural eutrophication or reflected natural conditions. Therefore, diatoms, algal pigments, okenone, geochemical proxies, and ²¹⁰Pb and ¹³⁷Cs were used in four sediment cores to investigate historical changes in trophic development, hypolimnetic redox conditions, anoxia and phototrophic sulphur bacteria abundances. Fossil diatoms, pigments, the ratio of chlorophyll derivatives to total carotenoids and the ratio of chlorophyll a to its derivatives suggest two phases of eutrophication coupled with hypolimnetic anoxia over the last ~80 years: a first phase from about 1923–1932 and a second from 1952 to 1982. In the first phase the ratios of Fe–Mn as well as Fe–Ca increased, suggesting seasonal anoxia. However, hypolimnetic anoxia was only weak because low levels of okenone suggest no mass development of sulphur bacteria. In contrast, sulphur bacteria increased during the early stages of the second eutrophication phase, suggesting increased temporal and spatial hypolimnetic anoxia. Surprisingly, the ratios of Fe–Mn as well as Fe–Ca decreased during this time. Possibly Fe, Mn and Ca were equally reduced through the intense anoxia. In the final stage, sulphur bacteria decreased again. As these bacteria need both anoxic conditions and a certain amount of light, the increased nutrient load probably led to low Secchi depth and therefore insufficient light conditions. In more recent years, diatoms and pigments suggest a decrease in nutrient levels. A second mass development of sulphur bacteria occurred, probably due to improved light conditions and continued anoxia in the upper hypolimnion. We conclude that the recent development of phototrophic sulphur bacteria do not represent natural conditions in Lake Dudinghausen. Furthermore, the upper sediments contain a completely new diatom flora that never occurred in older sediments of Lake Dudinghausen. Therefore, nutrient levels may eventually reach natural conditions, however they may not represent biological background reference conditions.     

Adaptations of microphytobenthos assemblages to sediment type and tidal position

Tagus intertidal microphytobenthos (MPB) assemblages were characterized over a wide range of sediment type and tidal height and the possible effects of these variables on MPB spatial distribution and photo-adaptation mechanisms were investigated. Two transects with six different sediment type and different tidal height sites were sampled once every two months from 2002 to 2004. Upper shore and sandy sites showed higher chlorophyll a (chl a) content, with sandy sediments showing a biomass peak in late winter–early spring, and muddy sites showing no obvious seasonal pattern. Stepwise multiple linear regressions showed that only SiO₂, tidal height and sediment particle size <63 μm were significant variables (p<0.05), explaining 50% of MPB biomass spatial–temporal variability. However, when data were separated by transect, only tidal height remained significant at both transects. Sandier sediments exhibited higher zeaxanthin/chl a and lower fucoxanthin/chl a ratios characteristic of a mixed cyanobacteria/diatom assemblages, showing an alternate seasonality with cyanobacteria increasing in summer and diatoms dominating in spring. Diatom biofilms showed contrasting features depending on the sediment type. Epipsammic diatoms were small with an average length of around 10 μm, while epipelic diatoms showed a wider size range with size distribution peaks at 10–15 μm, 25–35 μm and >60 μm. Epipelic biofilms showed evidence of being low light-acclimated (high fucoxanthin/chl a) and of photo-regulating by vertical migration movements (presence of endogenous vertical rhythms and lower diatoxanthin/diadinoxanthin). Epipsammic biofilms showed higher diatoxanthin/diadinoxanthin ratios and no vertical migration rhythms. Thus, the two diatom biofilm types had distinct strategies to photo-regulate: epipelic diatoms using vertical migration to position themselves at the sediment depth of optimum light conditions, and epipsammic diatoms using the xanthophyll cycle to photo-regulate. Further studies comparing epipsammic and epipelic assemblages are necessary to better understand MPB photo-regulation mechanisms.     

龙须菜对重金属汞胁迫的生理响应

研究了大型海藻龙须菜(Gracilaria lemaneiformis)对不同浓度重金属汞(0、0.02、0.04、0.10、0.20和0.40 mg/L)胁迫的生理响应.结果表明:当 Hg2+浓度逸0.02 mg/L 时,龙须菜藻体的相对生长速率显著下降,并且当 Hg2+浓度达到0.20和0.40 mg/L 时,龙须菜出现负增长.随着 Hg2+浓度的升高,龙须菜藻体的最大光化学量子产量、最大净光合速率和表观光合效率逐渐下降,叶绿素 a、类胡萝卜素和藻胆蛋白含量则呈先升高后下降的趋势,且当 Hg2+浓度逸0.10 mg/L 时,叶绿素 a、类胡萝卜素和藻胆蛋白含量显著下降.说明龙须菜在受 Hg2+胁迫的环境中耐受性较差,且 Hg2+对龙须菜的毒害作用较大,当Hg2+浓度逸0.02 mg/L 时,龙须菜藻体的生理活动就会受到显著抑制.