Microbial diversity and function in Antarctic freshwater ecosystems

Freshwater lakes occur through much of Antarctica and are characterized by short food chains dominated by microbes. Comparatively few studies have been made of continental freshwater lakes until recently, with the main emphasis being on the less extreme maritime Antarctic lakes. The wide range of trophic status seen at the northern extremes of the maritime Antarctic reduces markedly further south, but a wide range of micro-organisms occur throughout the latitudinal range. Information on seasonal and spatial patterns of microbial activity for freshwater lakes demonstrate rapid changes in community composition at certain times of year despite constant low temperatures. Benthic communities of cyanobacteria and bacteria are a feature of most lakes and are involved in a wide range of geochemical cycling. There is a need for more detailed taxonomic information on most groups and considerable potential for molecular studies.     

Global diversity of stoneflies (Plecoptera; Insecta) in freshwater

Plecoptera, or stoneflies, is a small order of hemimetabolous insects: according to our data, more than 3,497 species have been described so far in the world. The total number of species has enormously increased in the last 30 years (2,000 species estimated in 1976) and, if the trend continues, then it will nearly double in the near future. The order is divided into the suborders Arctoperlaria and Antarctoperlaria, and includes 16 families: 12 arctoperlarian and 4 antarctoperlarian. The Arctoperlaria account for a total number of 3,179 species, and Antarctoperlaria, only 318 species. The total number of genera is 286. We give in this article the estimated number of species for each family. The fauna and diversity of stonefly in North America (650 species reported) and Europe (426 species) are best known. Nevertheless, in the last 25 years, a mean of 2.6 Plecoptera species per year were described in Europe. Stonefly-faunas of Australia (191 species, Tasmania included) and New Zealand (104 species) are relatively well-known, while our knowledge of the Plecoptera of Central and South America (95 and 378 species respectively) is poor and still not representative of the real diversity. Africa has a reduced stonefly fauna (126 species). Asian stonefly diversity (approximately 1,527 species) is much greater than that of Europe or North America despite the fact that, except for Japan and Asiatic Russia that have been well studied, our knowledge of the remaining Asiatic areas is extremely poor. Even though our data indicate the Holarctic Region as the diversity hot-spot for the order, the analysis of the specific diversity divided by family suggests also an important role of tropical stoneflies. Guest editors: E.V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment     

Alpine freshwater ecosystems in a protected area: a source of diatom diversity

The “All Taxa Biodiversity Inventories” (ATBIs) project coordinated by the European Distributed Institute of Taxonomy (EDIT) aims to achieve a baseline biodiversity assessment of flora and fauna in those regions characterized by a lack of knowledge and a high potential for biodiversity. Within the framework of the ATBIs, the aim of this study was to analyse the diatom flora and ecology of a complex of freshwater ecosystems in the Maritime Alps Natural Park (Italy), designated as a Special area of Conservation under the European Habitat Directive. We sampled epilithic and epiphytic diatoms in different habitats in 24 sites: shallow lake, springs, and streams. Our analysis resulted in a list of 138 diatom taxa, highlighting the great biodiversity and the complex structure of the investigated diatom communities. The taxa list included a wide range of uncommon species, including some recorded for the first time in North-Western Italy. Among the different habitats the highest level of diversity was found in the more lentic waters, in particular in limnocrene springs. These results show that the diatom communities of pristine and undisturbed high-mountain environments are rich and complex, despite the severe environmental conditions.     

Zoosporic fungi in freshwater ecosystems

A review of the modern state of knowledge of zoosporic fungi in freshwater plankton and benthos is given. The effects of abiotic factors upon the distribution and development of these fungi are discussed, along with the problem of the role zoosporic fungi play in lake ecosystems.     

More refined diversity of anammox bacteria recovered and distribution in different ecosystems

A newly reported 16S rRNA gene-based PCR primer set was successfully applied to detect anammox bacteria from four ecosystem samples, including sediments from marine, reservoir, mangrove wetland, and wastewater treatment plant sludge. This primer set showed ability to amplify a much wider coverage of all reported anammox bacterial genera. Based on the phylogenetic analyses of 16S rRNA gene of anammox bacteria, two new clusters were obtained, one closely related to Candidatus Scalindua, and the other in a previously reported novel genus related to Candidatus Brocadia. In the Scalindua cluster, four new subclusters were also found in this study, mainly by sequences of the South China Sea sediments, presenting a higher diversity of Candidatus Scalindua in marine environment. Community structure analyses indicated that samples were grouped together based on ecosystems, showing a niche-specific distribution. Phylogenetic analyses of anammox bacteria in samples from the South China Sea also indicated distinguished community structure along the depth. Pearson correlation analysis showed that the amount of anammox bacteria in the detected samples was positively correlated with the nitrate concentration. According to Canonical Correspondence Analysis, pH, temperature, nitrite, and nitrate concentration strongly affected the diversity and distribution of anammox bacteria in South China Sea sediments. Results collectively indicated a promising application of this new primer set and higher anammox bacteria diversity in the marine environment.     

Glyphosate in northern ecosystems

Glyphosate is the main nonselective, systemic herbicide used against a wide range of weeds. Its worldwide use has expanded because of extensive use of certain agricultural practices such as no-till cropping, and widespread application of glyphosate-resistant genetically modified crops. Glyphosate has a reputation of being nontoxic to animals and rapidly inactivated in soils. However, recent evidence has cast doubts on its safety. Glyphosate may be retained and transported in soils, and there may be cascading effects on nontarget organisms. These processes may be especially detrimental in northern ecosystems because they are characterized by long biologically inactive winters and short growing seasons. In this opinion article, we discuss the potential ecological, environmental and agricultural risks of intensive glyphosate use in boreal regions.     

Warming alters the size spectrum and shifts the distribution of biomass in freshwater ecosystems

Organism size is one of the key determinants of community structure, and its relationship with abundance can describe how biomass is partitioned among the biota within an ecosystem. An outdoor freshwater mesocosm experiment was used to determine how warming of～4 °C would affect the size, biomass and taxonomic structure of planktonic communities. Warming increased the steepness of the community size spectrum by increasing the prevalence of small organisms, primarily within the phytoplankton assemblage and it also reduced the mean and maximum size of phytoplankton by approximately one order of magnitude. The observed shifts in phytoplankton size structure were reflected in changes in phytoplankton community composition, though zooplankton taxonomic composition was unaffected by warming. Furthermore, warming reduced community biomass and total phytoplankton biomass, although zooplankton biomass was unaffected. This resulted in an increase in the zooplankton to phytoplankton biomass ratio in the warmed mesocosms, which could be explained by faster turnover within the phytoplankton assemblages. Overall, warming shifted the distribution of phytoplankton size towards smaller individuals with rapid turnover and low standing biomass, resulting in a reorganization of the biomass structure of the food webs. These results indicate future environmental warming may have profound effects on the structure and functioning of aquatic communities and ecosystems.     

System controls on the aqueous distribution of mercury in the northern Florida Everglades

The forms and partitioning of aqueous mercury species in the canals and marshes of the Northern Florida Everglades exhibit strong spatial and temporal variability. In canals feeding Water Conservation Area (WCA) 2A, unfiltered total Hg (HgT_U) is less than 3 ng L^-1 and relatively constant. In contrast, methyl mercury (MeHg) exhibited a strong seasonal pattern, with highest levels entering WCA-2A marshes during July. Stagnation and reduced flows also lead to particle enrichment of MeHg. In the marshes of WCA-2A, 2B and 3A, HgT_U is usually <5 ng L^-1 with no consistent north–south patterns. However, for individual dates, aqueous unfiltered MeHg (MeHg_U) levels increase from north to south with generally lowest levels in the eutrophied regions of northern WCA-2A. A strong relationship between filtered Hg species and dissolved organic carbon (DOC), evident for rivers draining wetlands in Wisconsin, was not apparent in the Everglades, suggesting either differences in the binding sites of DOC between the two regions, or non-organic Hg complexation in the Everglades.     

Role of fungi in freshwater ecosystems

There are more than 600 species of freshwater fungi with a greater number known from temperate, as compared to tropical, regions. Three main groups can be considered which include Ingoldian fungi, aquatic ascomycetes and non-Ingoldian hyphomycetes, chytrids and, oomycetes. The fungi occurring in lentic habitats mostly differ from those occurring in lotic habitats. Although there is no comprehensive work dealing with the biogeography of all groups of freshwater fungi, their distribution probably follows that of Ingoldian fungi, which are either cosmopolitan, restricted to pantemperate or pantropical regions, or in a few cases, have a restricted distribution. Freshwater fungi are thought to have evolved from terrestrial ancestors. Many species are clearly adapted to life in freshwater as their propagules have specialised aquatic dispersal abilities. Freshwater fungi are involved in the decay of wood and leafy material and also cause diseases of plants and animals. These areas are briefly reviewed. Gaps in our knowledge of freshwater fungi are discussed and areas in need of research are suggested.     

River inter linking in India: status,issues, prospects and implications on aquatic ecosystems and freshwater fish diversity

India is a vast country in terms of natural resources and considered one of the mega- biodiversity countries in the world. The freshwater aquatic resources of the different river basins are unevenly distributed in space and time and the country is suffering from the increasing population and shortage of all kind of natural resources like water. To fulfill the water demand and mitigate flood and drought, Indian Government has been planning a huge scheme encompassing the Himalayas and most of India, by linking all major rivers through interlinking canals systems and building several dams. Though the concept of interlinking of rivers is novel and new in India, it had rather initiated long back in other countries of ancient civilization. This is considered as one of the options to remedy spatial mismatch in water availability and demand. To overcome those, National Water Development Agency (NWDA) has taken up massive project and nearly 30 links have been proposed to interlink the major rivers. The Government of India has approved the country’s first river interlinking project on Ken–Betwa and a MOU has been signed among the states of Uttar Pradesh and Madhya Pradesh and the Union Government. The feasibility report of most of the links have been completed and detailed project reports of Ken–Betwa River link is expected to be finalized soon. Our study indicated presence of rich fish diversity and threatened fishes in river Betwa and improved aquatic environment in river Ken which makes it a high priority area in view of proposed interlinking. The current state of knowledge indicates that large dams, interbasin transfers and water withdrawal from rivers have many negative as well as positive impacts on freshwater aquatic ecosystem. As regards to the impact on fish and aquatic biodiversity, there could be positive as well as negative impacts. The present paper is aimed at explaining and synthesizing the long term plan and its implications, creating baseline database, requirement of appropriate technology, manpower and related issues especially with reference to riverine aquatic ecosystem and conservation of fish biodiversity.     

再论生物多样性与生态系统的稳定性

本文在简述生物多样性与生态系统稳定性研究动态的基础上,从生物多样性和稳定性的概念出发,指出忽视多样性和稳定性的生物组织层次可能是造成观点纷争的根源之一。特定生物组织层次的稳定性可能更多地与该层次的多样性特征相关,探讨多样性和稳定性的关系应从不同的生物组织层次上进行,抗动是生态系统多样性与稳定性关系悖论中的重要因子,如果根据扰动的性质,把生态系统（或其他组织层次）区分为受非正常外力干扰和受环境因子时间异质性波动干扰2类系统,稳定性的4个内涵可以理解为：对于受非正常外力干扰的系统而言,抵抗力和恢复力是稳定性适宜的测度指标;对于受环境因子时间异质性波动干扰和系统而言。利用持久性和变异性衡量系统的稳定性则更具实际意义。结合对群落和种群层次多样性与稳定性相关机制的初步讨论,本文认为;在特定的前提下,多样性可以导致稳定性。     

陆地和淡水生态系统新型微生物氮循环研究进展

氮生物地球化学循环是地球物质循环的重要枢纽,是决定陆地生态系统生产力水平、水资源安全、温室气体生成排放的关键过程。氮循环是由微生物介导的一系列复杂过程,不同形态、价态氮化合物的转化分别由相应的功能微生物驱动完成。随着厌氧氨氧化、完全氨氧化等新型氮转化过程的相继报道和发现更新了人们对氮循环的认识。本文综述了陆地和淡水生态系统中厌氧氨氧化(anammox)、硝酸盐异化还原为铵(DNRA)、完全氨氧化(comammox)等新型氮循环过程的发生机制、热区分布及环境效应,并总结了这三种氮循环的相互关系。     

Exploring and quantifying fungal diversity in freshwater lake ecosystems using rDNA cloning/sequencing and SSU tag pyrosequencing

Water samples were collected along transects from the shore to the centre of two French lakes: the deep, volcanic, oligomesotrophic and low allochthonic-impacted Lake Pavin, and the productive and higher allochthonic-impacted Lake Aydat. The biodiversity was analysed using two approaches: the classical approach consisting of cloning/sequencing of the 18S, ITS1, 5.8S, ITS2 and partial 28S region using primers designed for fungus sequences, and the pyrosequencing of 18S rRNA hypervariable V2, V3 and V5 regions using two primer sets (one universal for eukaryotes and one for fungi). The classical approach yielded 146 (Lake Pavin) and 143 (Lake Aydat) sequences, corresponding to 46 and 63 operational taxonomic units (OTUs) respectively. Fungi represented half of the OTUs identified in Lake Pavin and 30% in Lake Aydat, and were dominated by sequences from Chytridiomycota found throughout Lake Pavin but mostly in the central pelagic zone of Lake Aydat. The pyrosequencing approach yielded 42,064 (Pavin) and 61,371 (Aydat) reads, of which 12-15% and 9-19% reads were assigned to fungi in Lakes Pavin and Aydat respectively. Chytridiomycota members were also dominant among these reads, with OTUs displaying up to > 33-fold overrepresentation in the centre compared with the riparian areas of Lake Aydat. Besides fungi, both approaches revealed other major eukaryote groups, with the highest diversity in the central areas of lakes. One of the major findings of our study was that the two lakes displayed contrasting spatial distributions, homogenous for Lake Pavin and heterogeneous for Lake Aydat, which may be related to their peculiarities. This study represents the first unveiling of microbial eukaryote and fungus diversity assessed with two complementary molecular methods, and is considered a major milestone towards understanding the dynamics and ecology of fungi in freshwater lake ecosystems, which are directly link to the abundance and distribution of taxa.     

北疆盐碱地植物群落空间分布及物种多样性

为探究盐碱地植物群落空间分布特征及群落间物种多样性的关系,根据对北疆盐碱地植物群落84个样点调查的数据,以各物种多度为指标,采用双向指示种分析方法（TWINSPAN）、除趋势对应分析法（DCA）、典范对应分析法（CCA）进行数量分类并分析群落分布与环境因子间关系和群落物种多样性及相似性变化特征。结果表明,TWINSPAN数量等级分类将84个样点的植物划分为11种类型。各群丛类型的物种多样性特征表现为群丛Ⅲ的多样性最大,群丛X多样性最小,且群丛Ⅲ多样性显著高于群丛X （P<0.05）,群丛VⅡ均匀度最大,群丛X均匀度最小,且群丛Ⅲ均匀度显著高于群丛X（P<0.05）,群丛I的丰富度最大,群丛X丰富度最小,且群丛I丰富度显著高于群丛X（P<0.05）,在所有群丛中群丛Ⅲ所含有的植物种类最多,有26种;相似性特征为群丛V和群丛VⅡ的相似性最大,群丛V和群丛VⅡ物种间的竞争较小,群丛稳定性高;CCA排序结果表明,北疆盐碱地植物群落分布与海拔高度、多年平均温度、土壤酸碱度等因素有关,其中影响最大的是海拔高度,其次为多年平均温度、降水量、蒸发量和土壤电导率,地形因子坡度对各群丛分布影响不大;北疆盐碱地植物群落数量分类及物种多样性变化的分析对于揭示北疆盐碱地植物群落空间分布特征和新疆盐碱地植物种质资源调查及其保护具有重要的意义。     

Viral abundance and genome size distribution in the sediment and water column of marine and freshwater ecosystems

The size distribution of viral DNA in natural samples was investigated in a number of marine, brackish and freshwater environments by means of pulsed field gel electrophoresis (PFGE). The method was modified to work with both water and sediment samples, with an estimated detection limit for individual virus genome size groups of 1-2 x 10(4) virus-like particles (VLP) mL(-1) water and 2-4 x 10(5) VLP cm(-3) sediment in the original samples. Variations in the composition and distribution of dominant virus genome sizes were analyzed within and between different habitats that covered a range in viral density from 0.4 x 10(7) VLP mL(-1) (sea water) to 300 x 10(7) VLP cm(-3) (lake sediment). The PFGE community fingerprints showed a number of cross-system similarities in the genome size distribution with a general dominance of genomes in the 30-48, 50-70 and 145-200 kb size fractions, and with many of the specific genome sizes detected in all the investigated habitats. However, large differences in community fingerprints were also observed between the investigated sites, and some virus genome sizes were found only in specific biotopes (e.g. lake water), in specific ecosystems (e.g. a particular lake) or even in specific microhabitats (e.g. a particular sediment stratum).     

Physiological and ecological controls on carbon sequestering in terrestrial ecosystems

Carbon cycling processes in ecosystems are generally believed to be well understood. Carbon, hydrogen, oxygen and other essential elements are chemically converted from inorganic to organic compounds primarily in the process of photosynthesis. Secondary metabolic processes cycle carbon in and among organisms and carbon is ultimately released back to the environment as CO₂ by respiratory processes. Unfortunately, our understanding of this cycle was determined under the assumption that the primary inorganic form of C (CO₂ in the atmosphere) was relatively constant. With the emerging concensus that atmospheric carbon concentration is increasing, we must now reassess our understanding of the carbon cycle. How will plants, animals and decomposers respond to a doubling of carbon supply? Will biological productivity be accelerated? If plant productivity increases will a predictable percentage of the increase be accumulated as increased standing crop? Or, is it possible that doubling the availability of CO₂ will increase metabolic activity at all trophic levels resulting in no net increase in system standing crop? The purpose of this paper is to review evidence for physiological and growth responses of plants to carbon dioxide enhancement. Essentially no research has been completed on the ecological aspects of these questions. From this review, I conclude that accurate predictions of future ecosystem responses to increasing atmospheric carbon dioxide concentration are not possible without additional understanding of physiological and ecological mechanisms.