Sources of organic matter in surface sediments of the Louisiana Continental margin: Effects of major depositional/transport pathways and Hurricane Ivan

Lignin and pigment biomarkers were analyzed in surface sediments of the Louisiana Continental margin (LCM) to distinguish differences in the degradative state of sedimentary organic matter along and between two major depositional pathways (along shore and offshore to the Mississippi Canyon) from Southwest (SW) Pass in July 2003. Barataria Bay, an inter-distributary estuary, was also assessed as a potential source of terrestrial organic matter to the LCM. Sediment signatures taken along the same pathways after Hurricane Ivan (October 2004) were compared with the pre-Ivan signature to elucidate carbon dynamics after major hurricane events. Density fractions were investigated at key stages across the LCM. Mississippi Canyon sediments are a depocenter for labile and refractory organic matter derived from river and previously deposited shelf sediments. Barataria Bay material may be a contributing source of sedimentary organic matter in shallow shelf areas bordering the bay and is thus potentially important in carbon cycling in sediments of these shallow areas; however, our results show that organic matter inputs from the bay were likely rapidly decomposed and/or diluted. Hurricane Ivan mobilized sedimentary organic carbon (SOC) offshore and homogenized terrestrial sediment parameters and gradients. As observed through pigment concentrations sediments tended to equilibrate to a more steady-state condition within months of the disturbance. Insights from density fractions show that selective degradation and aggregation/flocculation processes were also very important processes during cross-shelf transport. Zooplankton grazing, largely on diatoms and other algae, was a shelf wide phenomenon, however, grazing products dominated the marine-derived SOC in margin sediments west of the birdsfoot delta indicated by the abundance of steryl chlorin esters (SCEs).     

小麦麸皮水浸提液对铜绿微囊藻(Microcystis aeruginosa)光合色素含量和叶绿素荧光诱导动力学的影响

小麦麸皮水浸提液(WBL)对铜绿微囊藻(Microcystis aeruginosa)具有较强的抑制作用.为了阐明铜绿微囊藻光合系统对WBL胁迫的响应,本文分析了WBL胁迫下M.aeruginosa CHAB-109细胞光合色素含量及叶绿素荧光诱导动力学变化.结果显示,当WBL浓度为1.6和3.2 g/L时,M.aeruginosa CHAB-109单位细胞内Chl.a和类胡萝卜素含量均显著低于对照.Chl.a光诱导荧光动力学分析结果显示,WBL胁迫下单位反应中心吸收的光能(ABS/RC)、单位反应中心捕获的用于还原QA的能量(TR0/RC)及单位反应中心捕获的用于电子传递的能量(ET0/RC)均受到显著抑制.光合系统Ⅱ(PSⅡ)能量分配比率参数分析结果显示,WBL对光合系统反应中心电子供体侧没有影响,但是显著抑制光合系统反应中心电子受体侧电子传递.综合分析WBL诱导下M.aeruginosa CHAB-109 PSⅡ能量流动比活性能参数和能量分配比率参数显示,反应中心电子受体侧电子由反应中心传递到QA及QA更远的部位均为WBL的抑制作用位点.     

Evidence for short-lived oscillations in the biological records from the sediments of Lago Albano (Central Italy) spanning the period ca. 28 to 17 k yr BP

We report the results of analyses of pigments (derived from algae and photosynthetic bacteria), diatoms and invertebrate fossil remains (ostracods, cladocerans, chironomids) in two late Pleistocene sediment cores from Lago Albano, a crater lake in Central Italy. The record contains evidence for oscillations in lake biota throughout the period ca. 28 to 17 k yr BP. The earliest of these are contained in the basal 3.5 m of light olive-gray and yellowish-gray spotted muds sampled in core PALB 94-1E from 70 m water depth. The later oscillations are best represented in the more extended sediment sequence recovered from a second core site, PALB 94-6B, in 30 m water depth. The sediments at site 1E, containing the earlier oscillations (ca. 28-24 k yr BP), predate any sedimentation at the shallower site, from which we infer an initially low lake level rising to permit sediment accumulation at site 6B from ca. 24 k yr onwards. At site 6B, massive silts rich in moss remains are interbedded with laminated silts and carbonates. These sediments span the period ca. 24 to 17 k yr and are interpreted as representing, respectively, times of shallow water alternating with higher lake stands, when the lake was stratified and bottom water was stagnant. A range of mutually independent chronological constraints on the frequency and duration of the oscillations recorded in the lake biota indicate that they were aperiodic and occurred on millennial to century timescales. We interpret them as responses to climate forcing through its impact on lake levels and changing aquatic productivity. The time span they occupy, their frequency and their duration suggest that at least some of these changes may parallel both the Dansgaard-Oeschger events recorded in Greenland Ice Cores and the contemporary oscillations in North Atlantic circulation documented in marine sediment cores.     

不同品系条斑紫菜光合效率比较研究

用叶绿素荧光仪测试了7个品系紫菜叶状体在不同光照和温度条件下的光合效率,分析了受强光抑制后光合效率恢复的情况,并测试了这些品系的光合色素含量。结果显示,随着光照强度从20μmol.m-2.s-1提高到1 200μmol.m-2.s-1,总的趋势是光合效率逐渐降低,但下降幅度在不同品系间又有差异:相比20μmol.m-2.s-1光照下条件下光合效率,Yjs在1 200μmol.m-2.s-1时的光合效率下降了27%,Yw下降了33%,Gm下降了53%,Yqd下降了50%。在120μmol.m-2.s-1光照条件,5~20℃实验范围内,15~20℃条件下光合效率最高,除Yh2和Wjs,其它品系叶状体均在15℃达到顶峰,Yh2和Wjs则在20℃达到顶峰。在受到高光抑制(200μmol.m-2.s-1)后,处于光照60μmol.m-2.s-1,温度12℃条件下紫菜光合效率可在30~60 min内恢复。未发现光合色素含量与光合效率的相关性。文章还对紫菜光合效率与生态条件的关系进行了分析和讨论。     

表皮环割对花花柴(Kareliniacaspica)水势及光合参数的短期影响

生长在塔克拉玛干沙漠南缘的植物在生长季常遭受虫害和放牧的影响,频繁的干扰在很大程度上限制了该地区植物的生存和生长.以塔克拉玛干沙漠南缘策勒绿洲外围花花柴(Karelinia caspica)为试验材料,模拟干扰对于花花柴生理状况的短期影响,设置了对照(正常枝条)、中度环割(表皮环割50%)、重度环割(表皮环割100%),观测了环割后10 d内花花柴气孔导度、水势、光合色素、叶绿素荧光等在不同环割条件下的变化特征.结果显示:(1)除了类胡萝卜素(Car)含量外,中度环割对花花柴各项生理参数的影响不明显;(2)重度环割能够明显降低花花柴气孔导度、清晨水势和正午水势、叶绿素(Cal)含量和类胡萝卜素(Car)含量;(3)重度环割使得花花柴的光合原初反应遭到抑制,光系统Ⅱ(PSⅡ)结构和功能遭到损害,活性降低,光合器官对光能的吸收、传递、转化和电子捕获等过程也遭到抑制,用于耗散的能量显著增多.整体来看,重度环割下的花花柴短期内各项生理参数均出现显著降低,而中度环割下花花柴各项生理参数短期内变化不大.当人为或者昆虫、野兔等对花花柴表皮产生机械损伤时,表皮部分损伤的植物也许可以通过自身修复,使得各项生理机能恢复正常,而表皮遭受重度破坏的植物会随着时间的推移趋向于死亡.在荒漠化防治过程中,我们应该尽量避免花花柴的表皮被全部剥蚀.     

北冰洋中心区表层海水营养盐水平及浮游植物群落对快速融冰的响应

本文依托2010夏季中国第四次北极科学考察,通过对高纬度极地冰下水和冰芯的营养盐的连续观测及表层水颗粒物的藻类色素分析,获取了夏季快速融冰下冰水界面营养盐和光合色素的分布信息。结果表明调查期间表层水磷酸盐和硅酸盐相对于无机氮更丰富（依据Redfield比值）,表现为显著的氮限制。而冰芯无机氮浓度相对更高,融冰释放对水体无机氮有一定的补充。色素分析显示岩藻黄素（Fuco）和叶绿素a（Chl a）是水体颗粒物的主要光合色素。在8/15至8/18期间,叶绿素c（Chl c）、硅藻黄素（Diato）、硅甲藻黄素（Diadino）和岩藻黄素（Fuco）分别达到6,22,73和922μg/m3,体现了硅藻在群落中的优势地位。岩藻黄素（Fuco）的浓度在融冰快速期间有巨大的提升,主要来源于冰芯底部释放的衰老的冰生硅藻和浮游硅藻的生长。此外,青绿黄素（Prasino）和叶黄素（Lut）与岩藻黄素（Fuco）分布模式有明显的差异,暗示青绿藻和绿藻与硅藻对海冰融化的不同响应。     

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.     

Separation of phytoplanktonic pigments by HPLC for the study of phyto-zooplankton trophic relationships

Phyto-zooplankton trophic relationships were studied using phytoplanktonic pigments (chlorophylls and carotenoids) as organic natural markers. Pigments were separated by high-pressure liquid chromatography (HPLC).Comparison of pigment profiles from monospecific cultures of various taxonomic groups (Chlorophyceae, Bacillariophyceae and Cyanobacteria) and from Cladocera crustaceans (Daphnia magna) fed with these cultures, showed that the characteristic pigment associations of the different taxa are conserved during their transfer from primary producers to secondary consumers.Chromatographic profiles of the Bacillariophyceae and Chlorophyceae type were obtained fromDaphnia respectively fed with mixtures of a Chlorophyceae and a diatom species and mixture of a Chlorophyceae and a Cyanobacterium. This showed the importance of this method in demonstrating a possible selective feeding by the herbivorous zooplankton.The observation of pigment profiles of the Dinophyceae type following feeding of a zooplankton assemblage from Lake Pavin within this natural medium (phytoplankton dominated by a Dinophyceae) and of a Chlorophyceae type profile as the same assemblage was fed in the laboratory on phytoplankton from Lake Villerest (composed of about 80% Cyanobacteria and 20% Chlorophyceae), suggested that this method could be applied to the natural environment.     

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。     

Role of pigments on algal communities and photosynthesis

A one-year study of phytoplankton, primary production and related physical and chemical factors was made in a Swiss basin of Lake Lugano (Lago di Lugano). The chlorophylls and 12 carotenoids were analyzed with a TLC technique. The carotenoid monitoring was considered to be particularly interesting, because the role of these pigments in freshwater algae is still very poorly documented by field studies. The dependence of photosynthesis on several factors was statistically evaluated. Evidence was found of light-adaptation phenomena. The variations of photosynthetic activity and efficiency largely depended on the light regime in the few days before the field observations and on the cellular content of chlorophylls and single carotenoids, whose concentrations in their turn were closely linked with light, temperature, average cell size, and with the actual species assemblage.