Taxonomic Shift Over a Phosphorus Gradient Affects the Stoichiometry and Fatty Acid Composition of Stream Periphyton

Phosphorus enrichment of stream ecosystems generally increases primary production in the benthos, but the consequences of eutrophication for the nutritional quality of periphyton for grazers are less clear. On short timescales, high phosphorus inputs may lead to reduced C:P ratios and high essential fatty acid contents of periphyton, which are both considered important determinants of food quality for grazers. However, nutrient enrichment may alter the taxonomic composition of periphyton and favor the growth of less palatable algal taxa. In this study, periphyton was grown under a gradient of dissolved phosphorus availability from 5 to 100 µg P · L⁻¹, to investigate eutrophication effects on periphyton taxonomy, C:N:P stoichiometry, and fatty acid composition. After 1 month, periphyton grown under oligotrophic conditions was mainly composed of diatoms (~86%). With increasing phosphorus availability, diatoms were gradually outcompeted by chlorophytes and cyanobacteria, which were the predominant taxon under eutrophic conditions. Unexpectedly, periphyton C:P ratios increased with greater phosphorus supply, from ~280 under oligotrophic conditions up to ~790 at 100 µg · L⁻¹, reflecting a tendency of chlorophytes and cyanobacteria to produce more biomass per unit of assimilated phosphorus compared to diatoms. Periphyton content of essential polyunsaturated fatty acids relative to biomass followed a unimodal relationship with phosphorus availability and peaked at intermediate phosphorus levels, likely as a result of both taxonomic and nutrient effects. Our results demonstrate that phosphorus-driven eutrophication of freshwater ecosystems may worsen periphyton nutritional quality due to taxonomic sorting, which may further lead to lower growth and reproduction of herbivores.     

Effects of Stress from Mine Drainage on Diversity, Biomass, and Function of Primary Producers in Mountain Streams

This paper proposes a hypothesis that relates biodiversity, community biomass, and ecosystem function to a gradient of stress. According to this hypothesis, biodiversity has a low threshold of response to stress, whereas biomass and function are stable or increase under low to moderate stress and decrease only under high stress. This hypothesis was tested by examining communities of primary producers in streams under stress from mine drainage in the Rocky Mountains of Colorado, USA. Mine drainage exerts chemical stress (low pH, dissolved metals) as well as physical stress (deposition of metal oxides) on stream biota. Diversity of primary producers was usually more sensitive to stress from mine drainage than community biomass (chlorophyll a) or primary production. Diversity was negatively related to all stresses from mine drainage, but it was especially low in streams with low pH or high concentration of dissolved zinc. Biomass and production were high in streams with only chemical stress, but they were often low in streams with physical stress caused by metal oxide deposition. Stream sites with aluminum oxide deposition usually had very little algal biomass. The rate of metal oxide deposition, presence of aluminum oxides, and pH together explained 65% of the variation in biomass. The rate of net primary production was highly correlated with biomass and had a similar response to stress from mine drainage. Overall, chemical stresses (low pH, high concentration of zinc) generally led to the hypothesized trends in our model of ecosystems under stress. Physical stress (deposition of metal oxides), however, led to variable responses, and often decreased biomass and function even at low intensity, contrary to the original hypothesis. Thus, the nature of ecosystem response to stress may differ for chemical and physical stresses.     

贵州月亮山5种森林类型土壤生态化学计量特征研究

为了解贵州省月亮山森林土壤的化学计量特征,分层采集5种森林类型的土壤,测定C、N、P含量并分析化学计量特征。结果表明,5种森林类型0~20 cm土壤中变异最大的是P,20~100 cm土壤中变异最大的是C,最小的是N。5种森林类型0~10 cm土壤的C、N含量远高于中国陆地0~10 cm土壤的平均含量,而P含量远低于其平均含量。硬阔和软阔自然林土壤C、N、P含量存在明显差异,C含量为硬阔自然林软阔自然林,N和P含量基本呈现为软阔自然林硬阔自然林。不同森林类型土壤的C∶N为硬阔自然林软阔自然林,针阔混交林杉木和马尾松纯林。硬阔和软阔自然林、针阔混交林的C∶P、N∶P均随土层深度的增加而下降,而杉木和马尾松纯林的C∶P、N∶P随土层深度增加呈先下降后升高再下降的趋势,且均在30~50 cm处出现累积峰。相关分析表明0~100 cm土壤的C、N、P含量呈极显著正相关关系,土壤C含量、N含量与C∶N、C∶P、N∶P均呈极显著的正相关关系,P含量与C∶N呈极显著正相关关系(P0.001)。因此,贵州月亮山5种森林类型和不同土层的C、N、P含量及其化学计量特征存在显著差异。     

Phosphorus Availability Alters the Effects of Silver Nanoparticles on Periphyton Growth and Stoichiometry

Exposure to silver nanoparticles (AgNPs) may alter the structure and function of freshwater ecosystems. However, there remains a paucity of studies investigating the effects of AgNP exposure on freshwater communities in the natural environment where interactions with the ambient environment may modify AgNP toxicity. We used nutrient diffusing substrates to determine the interactive effects of AgNP exposure and phosphorus (P) enrichment on natural assemblages of periphyton in three Canadian Shield lakes. The lakes were all phosphorus poor and spanned a gradient of dissolved organic carbon availability. Ag slowly accumulated in the exposed periphyton, which decreased periphyton carbon and chlorophyll a content and increased periphyton C:P and N:P in the carbon rich lakes. We found significant interactions between AgNP and P treatments on periphyton carbon, autotroph standing crop and periphyton stoichiometry in the carbon poor lake such that P enhanced the negative effects of AgNPs on chlorophyll a and lessened the impact of AgNP exposure on periphyton stoichiometry. Our results contrast with those of other studies demonstrating that P addition decreases metal toxicity for phytoplankton, suggesting that benthic and pelagic primary producers may react differently to AgNP exposure and highlighting the importance of in situ assays when assessing potential effects of AgNPs in fresh waters.     

大别山山地次生林鸟类群落集团结构的季节变化

2007年12月—2008年12月,在大别山鹞落坪,对落叶阔叶次生林鸟类的集团结构的季节变化特征进行了研究。采用连续取样法采集鸟类取食行为数据,用聚类分析法对繁殖和非繁殖季节鸟类群落进行集团划分,通过无倾向对应分析（DCA）对32种森林鸟类的两个季节资源利用特点进行了研究。结果表明,鸟类群落在非繁殖季节可以分为地面、灌丛、树干（枝）、冠层等4个取食集团,而在繁殖季节还出现空中取食集团;候鸟影响鹞落坪次生林鸟类群落取食集团的结构,产生新的取食集团。DCA的第一轴主要代表鸟类取食高度信息,第二轴主要代表鸟类取食位置信息,第三轴代表鸟类取食方式和取食基质信息;用DCA前两轴对32种鸟类排序表明,有6种鸟主要在第一轴发生变化,有4种鸟主要在第二轴发生变化。     

Forest Structure and Primary Productivity in a Bornean Heath Forest

Aboveground forest structure, biomass, and primary productivity in a tropical heath forest in Central Kalimantan (Indonesian Borneo) were examined using data from 1-ha plots and stand-level allometric equations developed from harvested tree samples. The study site experienced a severe drought in 1997–1998 associated with the El Niño Southern Oscillation event. The drought effect on heath forest productivity was also assessed by evaluating changes in wood mass increment rates. Allometric relationships suggested that heath forest trees had leaves with smaller specific leaf area (SLA), and large heath forest trees allocate more to leaf mass compared to mixed dipterocarp forest trees. Aboveground biomass (for trees ≥ 4.8 cm DBH) in two 1-ha plots, P1 and P4, totaled 244.8 and 232.0 Mg/ha. Aboveground wood mass increment rate was –0.1 and 4.7 Mg/ha/yr in P1 and P4 during the drought period (from February to August 1998), while it quickly recovered to 8.1 and 8.5 Mg/ha/yr during the post-drought period (from August 1998 to August 1999 for P1 and from August 1998 to November 1999 for P4). This suggests a severe impact of the drought on heath forest productivity. Leaf characteristics of heath forest such as small SLA and long-lived leaves probably play a significant role in effective assimilation and maintenance of heath forest productivity under stressful conditions.     

大别山北坡落叶阔叶林的物种多样性

应用Simpson生态优势度指数（C）,Shannon—Wiener多样性指数（H）和均匀度（E）等指标,对落叶阔叶林的4个组合类型的物种多样性进行了分析。结果表明;乔木层树种的多样性指数H变化在1.4709-3.8875之间,以T_3（3.8875）最高,依次为T_4、T_2、T_1（1.4709）最低;均匀度E为T_3＞T_4＞T_1＞T_2,而生态优势度C与H的变化相反。表现出物种多样性不只受到海拔高度、生境条件的影响,人为活动、群落的稳定性等因素也有重要作用。相反,灌木层和草本层的物种多样性受人为活动的影响相对较小,表现出常规的变化,即随海拔升高,H和E值降低,C值则升高。格局检验的结果表明：栓皮栎种群为集群分布,短柄枹群呈随机分布。而化香种则呈现在化香林中的集群分布,在短柄枹林中又为随机分布的特点。     

长白山白桦林空间结构研究

于2006年在长白山建立了一个面积为5.2 hm2的次生白桦林永久样地,并对样地内的每株树木测量了坐标和胸径.运用混交度、大小比数和角尺度研究了该林分的空间结构.研究表明:该样地的平均混交度值为0.540,平均角尺度值为0.575.次生白桦林总体上处于中度混交水平,先锋树种和针叶树种的混交度高于其他类型的树种;次生演替的先锋树种在生长上处于优势,红松(Pinus koraiensis)、蒙古栎(Quercus mongolica)、水曲柳(Fraxinus mandshurica)等主要树种在该林分中处于劣态个体的比重高于先锋树种,槭属类植物处于劣态;次生白桦林总体上呈聚集分布格局.该林分的空间结构特点与所处的次生演替早期阶段和各个树种在林分中的地位、繁殖方式、更新策略以及采伐干扰等有关.     

秦岭太白山北坡蝗虫的群落结构

在秦岭太白山北坡23个样地内采集到蝗虫2总科7科25属34种。应用数量分类、多样性指数及相似性分析方法对太白山北坡蝗虫群落垂直分布样方资料进行了分析。应用数量分类法可将蝗虫群落按植被类型分为8种,即农耕带、栓皮栎林带、锐齿栎林带、辽东栎林带、桦木林带、冷杉林带、落叶松林带、高山草饲带。太白山蝗虫群落垂直分布规律明显。其中高海拔（如高山草甸带）的蝗虫种类数和多样性明显低于中低海拔,中低海拔（锐齿栎林带）蝗虫种类和多样性指数最大。但低海拔的农耕带人为干扰大,植被较单一,蝗虫优势种的优势度大,蝗虫密度大,而种类数较少。     

Tropical Forest Fragmentation Affects Floral Visitors but Not the Structure of Individual-Based Palm-Pollinator Networks

Despite increasing knowledge about the effects of habitat loss on pollinators in natural landscapes, information is very limited regarding the underlying mechanisms of forest fragmentation affecting plant-pollinator interactions in such landscapes. Here, we used a network approach to describe the effects of forest fragmentation on the patterns of interactions involving the understory dominant palm Astrocaryum mexicanum (Arecaceae) and its floral visitors (including both effective and non-effective pollinators) at the individual level in a Mexican tropical rainforest landscape. Specifically, we asked: (i) Does fragment size affect the structure of individual-based plant-pollinator networks? (ii) Does the core of highly interacting visitor species change along the fragmentation size gradient? (iii) Does forest fragment size influence the abundance of effective pollinators of A. mexicanum? We found that fragment size did not affect the topological structure of the individual-based palm-pollinator network. Furthermore, while the composition of peripheral non-effective pollinators changed depending on fragment size, effective core generalist species of pollinators remained stable. We also observed that both abundance and variance of effective pollinators of male and female flowers of A. mexicanum increased with forest fragment size. These findings indicate that the presence of effective pollinators in the core of all forest fragments could keep the network structure stable along the gradient of forest fragmentation. In addition, pollination of A. mexicanum could be more effective in larger fragments, since the greater abundance of pollinators in these fragments may increase the amount of pollen and diversity of pollen donors between flowers of individual plants. Given the prevalence of fragmentation in tropical ecosystems, our results indicate that the current patterns of land use will have consequences on the underlying mechanisms of pollination in remnant forests.     

梵净山黔周林的结构和动态

(一)黔椆(Cyclobalanopsis stewardiana)林主要分布于梵净山上部回香坪以上,剪刀峡及三王殿一牛尾河一带。它是贵州省所特有的群落类型。对梵净山海拔较高地区的常绿阔叶林一一黔椆林的结构和动态的分析表明,黔椆处于一种稳定的状态中,并保持着一种相对稳定的种的组成和结构。大量的幼苗和强有力的根出条的更新方式,使黔椆在群落中保持其优势地位,从而使黔椆林成为这一地区的“顶极植物群落”。(二)黔椆在海拔1150米开始出现;在1400一1700米一带成为常绿、落叶阔叶混交林内常绿树中的优势种;在1800—2100米,黔椆优势群落成为“顶极植物群落”,以及黔椆林下存在着大量的、仅在山体上部才有分布的大箭竹,说明黔椆林是对于这一高度地带的天然生境长期适应的结果。(三)在黔椆林中的大箭竹周期性成批枯死,这可能有利于黔椆的更新,因为黔椆树苗只能生长在林冠间隙的竹杆中间。大箭竹在黔椆林中大量相继枯死,这对于树的更新十分重要。     

A hot-spot of biodiversity in Northern Patagonia,Argentina

Located along the Argentine coastline of northern Patagonia, are San Matías (SMG) and San José (SJG) gulfs; although they are regarded as an area with a high-priority conservational status, knowledge on their diversity is currently fragmentary. Studies on molluscs from this area have been historically centred in economic resources and few works have referred to non-commercial species. The present study aims to document the biological diversity of molluscs at the SMG/SJG area, in order to determine the significance of these two gulfs in the context of the Argentine marine fauna; to evaluate how well represented is this fauna in three protected areas; and to compare the fauna present in the protected areas with that of a non-protected area. For that purpose, molluscs coming from 132 sampling stations, ranging from the intertidal to 170 m depth, were studied, and a thorough bibliographic compilation was performed. A total of 196 species of molluscs are reported for the area. Surprisingly, almost one third of these species lacked previous records for SMG/SJG, including several new/possibly new species. The three studied protected areas contain 88.3% of the species recognised for the entire SMG/SJG area. Although several species appear as exclusive from one of these three areas, many of them are also present in an intermediately located, non-protected area. Molluscan diversity at the SMG/SJG area is greater than previously thought, comprising about 41.4% of the bivalves and 37.8% of the gastropods present in the Argentine shelf; thus suggesting that the area may be considered as a hot-spot of diversity in the Argentine Sea.     

The Amphibian Chytrid Batrachochytrium dendrobatidis Occurs on Freshwater Shrimp in Rain Forest Streams in Northern Queensland, Australia

Chytridiomycosis is a disease of amphibians caused by the chytrid fungus Batrachochytrium dendrobatidis. It can be highly virulent and is unusual in that it appears to drive many host species to local extinction during outbreaks. One mechanism that could facilitate this is the ability to grow saprophytically or on alternative hosts. This is common in other chytrids but has not been demonstrated for B. dendrobatidis in the field. B. dendrobatidis can grow on arthropod exoskeletons in the laboratory, and freshwater shrimp can be the most abundant animals in tropical rain forest streams. We therefore used diagnostic quantitative polymerase chain reaction to determine the infection status of freshwater shrimp from areas in which they are sympatric with frog species that have suffered declines in association with outbreaks of chytridiomycosis. We detected B. dendrobatidis on three individual shrimp belonging to two genera and collected from two widely separated streams. Two of the individuals had high levels of infection. This indicates that the presence of alternative hosts is likely to contribute to the extreme virulence of chytridiomycosis outbreaks in some systems. The presence of alternative hosts may allow B. dendrobatidis to remain in the environment after local extinctions of amphibian hosts, preventing the recovery of amphibian populations.     

青海互助北山国家森林公园不同生境的蝶类多样性研究

为了进一步探讨高海拔地区蝴蝶种类和数量与生境结构之间的关系,1993–1997年每年的7月对互助北山国家森林公园不同生境类型(谷间平原、温性草原、针阔叶混交林、高寒灌丛草甸)中蝶类群落的结构、数量和多样性进行了调查。共获得蝴蝶标本4,745头,86种,隶属于8科57属。种类较丰富的类群主要有:粉蝶科豆粉蝶属(Colias)6种、菜粉蝶属(Pieris)5种、绢粉蝶属(Aporia)4种、云粉蝶属(Pontia)3种,蛱蝶科网蛱蝶属(Melitaea)3种;个体数量以粉蝶科和灰蝶科为最多。不同的生境蝶类在种类组成和个体数量上有明显差异,其中以针阔叶混交林物种数(44种)最多,谷间平原个体数量(1,969只)最多。物种多样性指数以针阔叶混交林中最高,高寒灌丛草甸最低;均匀度以针阔叶混交林最高,谷间平原最低;优势度以高寒灌丛草甸最高。从不同生境蝶类成分的特有性上分析,特有属和特有种含量高低依次为针阔叶混交林(20属24种)>高寒灌丛草甸(8属8种)>谷间平原(6属7种)>温性草原(5属6种)。不同生境类型间蝶类种类的相似性系数在0–0.4259之间。蝶类种类组成的聚类分析结果显示:谷间平原与温性草原最先聚为一类,然后与针阔叶混交林聚为一类,最后与高寒灌丛草甸聚为一类。为保护该地区的蝶类物种多样性,应加大宣传力度,建立自然保护区,继续加强本底资源调查。     

祁连山5种典型灌丛土壤生态化学计量特征

土壤C、N、P生态化学计量特征是体现生态系统变化过程的重要依据。该研究以分布于祁连山北麓中段的甘青锦鸡儿、鲜黄小檗、金露梅、鬼箭锦鸡儿、吉拉柳等5种典型灌丛群落为研究对象,通过野外调查采样,测定土壤有机C、N、P含量,分析了不同灌丛群落土壤C、N、P含量及其生态化学计量比的垂直分布特征,并探讨了各指标间的耦合关系,为祁连山地区土壤-植物养分关系及退化植被恢复与重建提供理论依据。结果表明:(1)祁连山北麓中段5种灌丛群落土壤有机C(45.29 g/kg)、全N(3.85 g/kg)、全P含量(0.70 g/kg)较高,均高于全国平均水平。(2)相关性分析表明,土壤有机C与全N之间呈极显著正相关(P0.01),但土壤有机C与全P以及全N与全P之间没有明显的相关性,且土壤C、N含量变化几乎完全同步。(3)各灌丛类型土壤有机C、全N含量均表现为表层高于下层,而全P含量土层间差异不显著;各灌丛群落土壤有机C、全N含量均随土层加深呈现"倒金字塔"的分布格局,但不同灌丛类型全P含量随土层加深的变化规律却不一致,且土层对全P含量的影响不显著。(4)5种灌丛群落土壤整体C∶N、C∶P、N∶P(11.29、66.99、5.67)均低于全国平均水平,各灌丛群落土壤C∶P、N∶P随土层加深均呈不同程度的下降趋势,但不同灌丛群落土壤C∶N随土层加深的变化规律有所不同。(5)土壤有机C、全N与C∶N、C∶P、N∶P之间均具有极显著的二次函数关系(P0.01),土壤全P与C∶N、C∶P、N∶P之间关系不显著。研究认为,祁连山北麓中段土壤C∶N和P含量的稳定性较高(CV=3.99%和2.66%),C∶P、N∶P是判断研究区限制性养分的重要指标,祁连山北麓中段灌丛群落土壤主要受N素的限制。     

Thylakoid Membrane Reduction Affects the Photosystem Stoichiometry in the Cyanobacterium Synechocystis sp. PCC 6803

Biogenesis of thylakoid membranes in both chloroplasts and cyanobacteria is largely not understood today. The vesicle-inducing protein in plastids 1 (Vipp1) has been suggested to be essential for thylakoid membrane formation in Arabidopsis (Arabidopsis thaliana), as well as in the cyanobacterium Synechocystis sp. PCC 6803, although its exact physiological function remains elusive so far. Here, we report that, upon depletion of Vipp1 in Synechocystis cells, the number of thylakoid layers in individual Synechocystis cells decreased, and that, in particular, the content of photosystem I (PSI) complexes was highly diminished in thylakoids. Furthermore, separation of native photosynthetic complexes indicated that PSI trimers are destabilized and the monomeric species is enriched. Therefore, depletion of thylakoid membranes specifically affects biogenesis and/or stabilization of PSI in cyanobacteria.In chloroplasts and cyanobacteria the energy transfer between PSI and PSII is regulated in a light-dependent manner (for a recent review, see Kramer et al., 2004). The two photosystems are connected by the cytochrome b₆f complex, and electron transfer from PSII via the cytochrome b₆f complex to PSI is believed to be regulated by the redox state of the plastoquinol pool potentially also involving the cytochrome b₆f complex (Fujita et al., 1987; Murakami and Fujita, 1993; Schneider et al., 2001, 2004; Pfannschmidt, 2003; Volkmer et al., 2007). Transfer of light energy to the two photosystems is mediated by light-harvesting complexes, and in cyanobacteria light is harvested by the soluble extramembranous phycobilisomes. The efficient energy transfer to PSI and PSII has to be balanced to synchronize the function of the two photosystems. In response to changing light intensities and qualities, energy coupling between the phycobilisomes and the photosystems changes, which allows a rapid adjustment of light absorbance by the individual photosystems. Furthermore, besides this short-term adaptation mechanism, it has been shown in many studies that on a longer term in cyanobacteria the ratio of the two photosystems changes depending on the light conditions (Manodori and Melis, 1986; Murakami and Fujita, 1993; Murakami et al., 1997). Upon shifting cyanobacterial cells from low-light to high-light growth conditions, the PSI-to-PSII ratio decreases due to selective suppression of the amount of functional PSI. In recent years, some genes have already been identified that are involved in this regulation of the photosystem stoichiometry (Hihara et al., 1998; Sonoike et al., 2001; Fujimori et al., 2005; Ozaki et al., 2007).Whereas in chloroplasts of higher plants and green algae the amounts of the two photosystems change in response to changing light conditions (Melis, 1984; Chow et al., 1990; Smith et al., 1990; Kim et al., 1993), it has already been noted a long time ago that the chloroplast ultrastructure also adapts to high-light and low-light conditions (Melis, 1984). Chloroplasts of plants grown under low light or far-red light have more thylakoid membranes than chloroplasts of plants grown under high light or blue light (Anderson et al., 1973; Lichtenthaler et al., 1981; Melis and Harvey, 1981). There appears to be a direct correlation between the chlorophyll content and the amount of thylakoids per chloroplast because light harvesting is increased by enhanced chlorophyll and thylakoid membrane content per chloroplast. Thus, chloroplasts adapt to high light both by a reduction of thylakoid membranes and by a decrease in the PSI-to-PSII ratio.Thylakoid membranes are exclusive features of both cyanobacteria and chloroplasts, and it still remains mysterious how formation of thylakoid membranes is organized. Many cellular processes, like lipid biosynthesis, membrane formation, protein synthesis in the cytoplasm and/or at a membrane, protein transport, protein translocation, and protein folding have to be organized and aligned for formation of internal thylakoid membranes. The recent observation that deletion of the vipp1 gene in Arabidopsis (Arabidopsis thaliana) results in complete loss of thylakoid membranes has indicated that Vipp1 is involved in biogenesis of thylakoid membranes. Further analysis has suggested that Vipp1 could be involved in vesicle trafficking between the inner envelope and the thylakoid membrane of chloroplasts (Kroll et al., 2001). Because of this, the protein was named Vipp1, for vesicle-inducing protein in plastids 1. Depletion of Vipp1 strongly affected the ability of cyanobacterial cells to form proper thylakoid membranes (Westphal et al., 2001) and, consequently, also in cyanobacteria Vipp1 appears to be involved in formation of thylakoid membranes. A Vipp1 depletion strain of Arabidopsis is deficient in photosynthesis, although the defect could not be assigned to a deficiency of a single photosynthetic complex, but appeared to be caused by dysfunction of the entire photosynthetic electron transfer chain (Kroll et al., 2001). Therefore, depletion of Vipp1 in Arabidopsis seems to affect thylakoid membrane formation rather than the assembly of thylakoid membrane protein complexes (Aseeva et al., 2007). However, for cyanobacteria, it is not clear yet how diminishing the amount of thylakoid membrane layers would affect the amount and stoichiometry of the two photosystems.Here, we present the generation and characterization of a Vipp1 depletion strain of the cyanobacterium Synechocystis sp. PCC 6803. Upon depletion of Vipp1, a decrease in thylakoid membrane pairs in the generated mutant strain and, furthermore, a significant decrease in active PSI centers was observed. Moreover, trimerization of PSI also appeared to be impaired in the mutant strain. These results suggest that thylakoid membrane perturbations caused by the Vipp1 depletion directly affects PSI assembly and stability in cyanobacterial thylakoid membranes.     

Patterns in the Chemical Fractionation of Organic Nitrogen in Rocky Mountain Streams

The intraannual dynamics of particulate organic nitrogen (PON) and two fractions of dissolved organic nitrogen (DON) were investigated in two Rocky Mountain streams draining watersheds with low rates of N deposition. Organic nitrogen accounted for over 60% of the total annual nitrogen export and consisted mostly of DON. Nitrate peaked during winter months and declined considerably during the growing season (less than 10 µg/L) suggesting the importance of biotic uptake. Concentrations of PON, total DON, and two DON fractions (humic and non-humic) peaked during spring runoff and were positively related to discharge, indicating hydrologic influence. Total DON and its two fractions showed significant inverse relationships to nitrate, indicating that DON and nitrate followed different intraannual patterns. Despite its seasonal fluctuations in concentration, PON showed a consistent carbon–nitrogen (C:N) ratio suggesting that it was relatively uniform in composition. Fractionation studies indicated that DON was primarily of non-humic origin, whereas dissolved organic carbon (DOC) was mainly derived from humic sources. The two DON fractions differed from each other in seasonal patterns of concentration and C:N ratio. The proportion of humic DON increased during snowmelt, and there were diverging seasonal patterns in the C:N ratio of the two fractions implying variations in bioavailability. Although organic nitrogen is commonly treated as a single pool in ecological studies, our results indicated that DON consists of fractions that undergo large intraannual changes in proportions and chemical composition. Treatment of DON as a single pool may be misleading from the viewpoint of understanding ecosystem processes directly related to changes in its sources and biological reactivity.     

长白山北坡岳桦种群结构及动态分析

以“空间代时间”的方法 ,以种群径级结构代替年龄结构 ,采用静态生命表、生存分析和空间格局分析方法 ,探讨了长白山北坡不同海拔分布的岳桦种群的结构和动态规律。结果表明 ,在海拔 180 0、190 0和 2 0 0 0m ,随海拔升高 ,岳桦种群密度增大 ,径级分布范围减小 ,种群存活曲线由DeeveyⅡ型过渡到DeeveyⅠ型 ,种群由稳定型过渡为增长型 ,说明岳桦种群由低海拔向高海拔 ,群落处于不同的演替和发展阶段。而且随着岳桦径级的增大 ,其分布格局由集群分布过渡到随机分布。