Microbial genetic diversity and ciliate community structure along an environmental gradient in coastal soil

We investigated the microbial genetic diversity and ciliate community in coastal soil from five sites with an environmental gradient using denaturing gradient gel electrophoresis (DGGE), gene sequencing and the Ludox–QPS method. The analyses of both the 16S ribosomal RNA (rRNA) gene and 18S rRNA gene DGGE resulted in equal or even a higher number of bands found in the samples taken from the high-salinity sites IV and V than in those taken from the low-to-moderate-salinity sites I–III. Cluster analysis of both DGGE profiles classified the five sites into three main groups (sites I, II and III and IV and V), which corresponded well to the analysis of environmental factors. There were 13 species observed at site I, three species at site II and nine species at site III, while no active ciliates were observed at the high-salinity sites IV and V. By contrast, the ciliate-specific DGGE revealed a higher number of bands in the samples taken from the high-salinity soil. Furthermore, gene sequencing suggested that the ciliates in the high-salinity soil comprised forms originating not only from soil but also from marine environments. The data indicate that saline soil may maintain a high diversity of ciliates and soil salinity might be the most influential factor regulating the community structure of ciliates.     

Microbial community structure along an altitude gradient in three different localities

The microbial community structure along an altitude gradient was investigated in different localities, in Kalasi lake, Urumqi river and Sangong river, Xingjiang (China). The mean numbers of DAPI (4',6-diamidino-2-phenylindole)-stained cells were lower in Kalasi lake than that in Urumqi river and Sangong river; these differences were attributed to increasing environmental harshness including lower soil organic carbon and nitrogen content, more acidic pH and lower annual temperature. In each locality, the numbers of bacteria and archaea measured with two fluorescence-labeled 16S rRNA oligonucleotide probes (EUB338 and ARCH915) were higher in a coniferous forest and lower in desert vegetation. A significant and positive relationship was found between microbial and soil organic carbon and total nitrogen along the altitudinal gradient, indicating that plant communities and soil nutrients influence the soil microbial structure. The results show that the microbial population in higher latitudinal site was fewer than lower latitudinal one, soil microorganisms were positively correlated to soil organic carbon and total nitrogen, and plant communities had an obviously impact on soil microbes.     

Afforestation alters community structure of soil fungi

Relatively little is known about the effect of afforestation on soil fungal communities. This study demonstrated that afforestation altered fungal community structure and that changes were correlated to pools of soil C. Pasture at three locations on the same soil type was afforested with Eucalyptus globulus or Pinus pinaster. The structure of fungal communities under the three land uses was measured after 13y using automated ribosomal intergenic spacer analysis (ARISA). Afforestation significantly altered the structure of fungal communities. The effect of location on the structure of fungal communities was limited to pasture soils; although these contained the same plant species, the relative composition of each species varied between locations. Differences in the structure of fungal communities between pasture, E. globulus and P. pinaster were significantly correlated with changes in the amount of total organic C and microbial biomass-C in soil. Afforestation of patches of agricultural land may contribute to conserving soil fungi in agricultural landscapes by supporting fungal communities with different composition to agricultural soils.     

不同海拔缓步动物群落结构的比较

为研究海拔对缓步动物群落结构的影响,对地处秦岭北坡的南五台山缓步动物群落进行了初步调查研究.调查设置3个样区、45个样方,共采集缓步动物919个,个体密度平均816.89个·m-2,隶属缓步动物门2纲2目3科7属11种.其中Macrobiotus hufelandi和M.harmsworthi共占总采量的92.93%,为优势类群.采用Simpson指数、Shannon-Wiener信息指数、Pielou均匀度指数和修正的Hill指数来计算各生境缓步动物群落结构特点.研究表明,海拔对缓步动物群落结构有一定的影响.随着海拔的下降其物种的个体数量、群落优势类群的数量和优势物种数都呈下降趋势;物种多样性的变化趋势为中海拔地区＞低海拔地区＞高海拔地区,而群落优势度的变化趋势完全相反;不同海拔样区的群落相似性较低.     

Macrofaunal community bioturbation along an estuarine gradient

A multidisciplinary study of the impact of bioturbation on sediment dynamics has been underway for some time at the Plymouth Marine Laboratory. The current programme has been founded upon the careful selection of six sites in the River Tamar, representative of important combinations of physical and biological variables. The paper presents preliminary results illustrating the contrasting importance of the speciesNereis diversicolor andNephtys hombergi as agents of bioturbation, given their different distributions across the six sites. Thus bioirrigation byN. diversicolor increases up the estuary and is greatest in the region of high suspended bed-load due to tidal pumping, where the consequences for chemical exchange processes between sediments and the water column may be most important. The sediment mixing effects ofN. hombergi are likely to be greater towards the seaward end of the estuary but ultimately the particular sediment types and the macrofaunal communities they support dictate the level of bioturbation in ways that do not necessarily relate to simple axial gradients along the estuary.     

藏东南森林土壤微生物群落结构与土壤酶活性随海拔梯度的变化

【目的】针对青藏高原藏东南地区色季拉山不同海拔森林土壤,探讨微生物群落与土壤酶活性之间的联系以及受控因子。【方法】利用微生物细胞膜磷脂(PLFA)方法研究土壤微生物群落结构随海拔变化情况,分析土壤葡萄糖苷酶、酚氧化酶、蛋白酶、L-天冬酰胺酶、脲酶和酸性磷酸酶活性以及土壤理化性质随海拔的变化趋势。【结果】土壤理化性质和生化指标随海拔增高没有显著变化,如水分含量、有机碳、全氮、碳氮比、pH、无机氮和硝态氮,土壤葡萄糖苷酶、酚氧化酶、蛋白酶、L-天冬酰胺酶和酸性磷酸酶活性等;然而,微生物丰度呈现中峰优势分布规律,细菌、真菌、革兰氏阳性菌、革兰氏阴性菌和放线菌含量在海拔3 900 m和4 000 m处生物量显著高于低海拔和更高海拔。皮尔森相关性分析表明土壤pH是影响微生物群落结构的主要因子,但海拔梯度上的温度变化与微生物群落结构和酶活性不存在显著相关性;同时,有机碳、全氮、水溶性有机碳和水溶性有机氮和pH等理化指标与土壤酶活性显著相关。【结论】在藏东南色季拉山森林生态系统,海拔梯度对土壤微生物群落结构影响较大,土壤理化指标与生物特征对海拔梯度的响应较弱。     

中亚热带森林土壤微生物群落多样性随海拔梯度的变化

运用Biolog EcoPlate技术, 对武夷山不同海拔植被带(常绿阔叶林(EBF)、针叶林(CF)、亚高山矮林(DF)、高山草甸(AM))土壤微生物群落多样性差异进行了研究。结果表明: 不同海拔植被带土壤微生物群落功能多样性差异显著。土壤平均颜色变化率(AWCD)随培养时间延长而逐渐增加, 同一深度土层的AWCD值随海拔升高而逐渐降低, 大小顺序依次为EFB > CF > DF > AM。同一海拔植被带, 不同深度土层的AWCD值总体趋势依次为0-10 cm > 10-25 cm > 25-40 cm。土壤微生物群落Simpson指数、Shannon-Wiener指数、丰富度指数和McIntosh指数的总体趋势为EBF最高, CF和DF次之, AM最低。不同海拔植被带土壤微生物对不同碳源利用强度存在较大差异, 其中EBF利用率最高, AM利用率最低, 碳水化合物和羧酸类碳源是各海拔植被带土壤微生物的主要碳源。主成分分析结果表明, 从31个因素中提取的与碳源利用相关的主成分1、主成分2分别能解释变量方差的75.27%和16.14%, 在主成分分离中起主要贡献作用的是胺类和氨基酸类碳源。土壤微生物群落多样性随着海拔上升、土层加深而逐渐下降的原因, 可能是生物量、林分凋落物、土壤养分、微小动物、植物根系等多种因素共同作用的结果。     

Synthetic sheep urine alters fungal community structure in an upland grassland soil

Agricultural improvement (fertilisation, liming, intensification of grazing) of acidic upland pastures results in loss of indigenous flora and notable changes in microbial community structure. Such practices have recently raised concerns regarding the possible impacts on natural ecosystem biodiversity and functioning. The effects of synthetic sheep urine (SSU) and plant species on fungal community structure in upland grassland microcosms were investigated. Plant species typical of agriculturally unimproved (Agrostis capillaris) and improved (Lolium perenne) pastures were treated with low, medium or high concentrations of SSU, with harvests carried out 10 d and 50 d after SSU application. Root biomass was negatively affected by SSU addition whereas shoot biomass did not display any significant change. Fungal richness (number of operational taxonomic units) was negatively correlated with SSU concentration (p < 0.001), and also with time (p < 0.001).Multi-dimensional scaling plots revealed significant changes in fungal community composition, depending on concentration of SSU and plant species type, while canonical correspondence analysis also emphasised the importance of interacting environmental variables. In addition, SIMPER analyses supported the finding that shifts in fungal community composition under different SSU and plant treatments had occurred. Overall, while SSU appeared to be influential in determining fungal community structure, community changes were largely driven by interacting environmental factors. This study contributes to our understanding of the potential implications of intensified farming, in particular increased pressure from grazing animals, on fungal community structure in semi-natural grassland systems.     

Hypolithic and soil microbial community assembly along an aridity gradient in the Namib Desert

The Namib Desert is considered the oldest desert in the world and hyperarid for the last 5 million years. However, the environmental buffering provided by quartz and other translucent rocks supports extensive hypolithic microbial communities. In this study, open soil and hypolithic microbial communities have been investigated along an East–West transect characterized by an inverse fog-rainfall gradient. Multivariate analysis showed that structurally different microbial communities occur in soil and in hypolithic zones. Using variation partitioning, we found that hypolithic communities exhibited a fog-related distribution as indicated by the significant East–West clustering. Sodium content was also an important environmental factor affecting the composition of both soil and hypolithic microbial communities. Finally, although null models for patterns in microbial communities were not supported by experimental data, the amount of unexplained variation (68–97 %) suggests that stochastic processes also play a role in the assembly of such communities in the Namib Desert.     

亚热带森林土壤微生物生物量及群落功能特征的城乡梯度变化

土壤微生物在土壤养分循环以及生物地球化学循环中起着重要作用,土壤微生物对环境变化响应灵敏.为研究城乡梯度环境变化对亚热带森林土壤微生物的影响,本研究选取合肥市大蜀山国家森林公园(城市林)、紫蓬山国家森林公园(远郊林)、六安市万佛山(乡村自然林)为样地,分析比较其微生物生物量碳(MBC)、微生物生物量氮(MBN)及微生物...     

Bacterial diversity,community structure and potential growth rates along an estuarine salinity gradient

Very little is known about growth rates of individual bacterial taxa and how they respond to environmental flux. Here, we characterized bacterial community diversity, structure and the relative abundance of 16S rRNA and 16S rRNA genes (rDNA) using pyrosequencing along the salinity gradient in the Delaware Bay. Indices of diversity, evenness, structure and growth rates of the surface bacterial community significantly varied along the transect, reflecting active mixing between the freshwater and marine ends of the estuary. There was no positive correlation between relative abundances of 16S rRNA and rDNA for the entire bacterial community, suggesting that abundance of bacteria does not necessarily reflect potential growth rate or activity. However, for almost half of the individual taxa, 16S rRNA positively correlated with rDNA, suggesting that activity did follow abundance in these cases. The positive relationship between 16S rRNA and rDNA was less in the whole water community than for free-living taxa, indicating that the two communities differed in activity. The 16S rRNA:rDNA ratios of some typically marine taxa reflected differences in light, nutrient concentrations and other environmental factors along the estuarine gradient. The ratios of individual freshwater taxa declined as salinity increased, whereas the 16S rRNA:rDNA ratios of only some typical marine bacteria increased as salinity increased. These data suggest that physical and other bottom-up factors differentially affect growth rates, but not necessarily abundance of individual taxa in this highly variable environment.     

猫儿山不同海拔植被带土壤微生物群落功能多样性

为研究中亚热带森林土壤微生物群落功能多样性特征及其随海拔梯度的变化,应用Biolog微平板技术,对猫儿山不同海拔植被带(常绿阔叶林(EBF)、落叶阔叶混交林(DBF)、针阔混交林(CBF))土壤微生物群落功能多样性差异进行了比较。结果表明,不同海拔植被带土壤微生物群落功能多样性差异显著。土壤平均颜色变化率(AWCD)随培养时间延长而逐渐增加,随着海拔升高,土壤AWCD值逐渐降低,大小顺序为EBFDBFCBF。土壤微生物群落Shannon指数和丰富度指数的总体趋势为EBF最高,DBF次之,CBF最低。不同海拔植被带土壤微生物群落均匀度指数之间差异不显著。不同海拔植被带土壤微生物对不同碳源的利用能力存在差异,其中EBF利用率最高,CBF利用率最低,氨基酸类、胺类和酯类碳源为各海拔植被带土壤微生物利用的主要碳源。主成分分析结果表明,主成分1和主成分2分别能解释变量方差的40.42%和15.97%,在主成分分离中起主要贡献作用的是酯类、胺类和氨基酸类碳源。土壤理化性质与土壤微生物群落功能多样性之间的相关性分析结果表明,微生物群落多样性的Shannon指数与全钾(TK)呈极显著正相关(P0.01),与含水量呈极显著负相关(P0.01),与总有机碳(TOC)、全氮(TN)、速效氮(AN)、有效P(AP)之间的相关性显著(P0.05)或极显著(P0.01),且为负相关。土壤TK含量和含水量可能是造成不同海拔土壤微生物群落功能多样性差异的主要原因。     

Scavenger community structure along an environmental gradient from boreal forest to alpine tundra in Scandinavia

Scavengers can have strong impacts on food webs, and awareness of their role in ecosystems has increased during the last decades. In our study, we used baited camera traps to quantify the structure of the winter scavenger community in central Scandinavia across a forest–alpine continuum and assess how climatic conditions affected spatial patterns of species occurrences at baits. Canonical correspondence analysis revealed that the main habitat type (forest or alpine tundra) and snow depth was main determinants of the community structure. According to a joint species distribution model within the HMSC framework, species richness tended to be higher in forest than in alpine tundra habitat, but was only weakly associated with temperature and snow depth. However, we observed stronger and more diverse impacts of these covariates on individual species. Occurrence at baits by habitat generalists (red fox, golden eagle, and common raven) typically increased at low temperatures and high snow depth, probably due to increased energetic demands and lower abundance of natural prey in harsh winter conditions. On the contrary, occurrence at baits by forest specialists (e.g., Eurasian jay) tended to decrease in deep snow, which is possibly a consequence of reduced bait detectability and accessibility. In general, the influence of environmental covariates on species richness and occurrence at baits was lower in alpine tundra than in forests, and habitat generalists dominated the scavenger communities in both forest and alpine tundra. Following forecasted climate change, altered environmental conditions are likely to cause range expansion of boreal species and range contraction of typical alpine species such as the arctic fox. Our results suggest that altered snow conditions will possibly be a main driver of changes in species community structure.     

Virioplankton community structure along a salinity gradient in a solar saltern

The virioplankton community structure along a salinity gradient from near seawater (40 per thousand ) to saturated sodium chloride brine (370 per thousand ) in a solar saltern was investigated by pulsed-field gel electrophoresis. Viral populations with genome sizes varying from 10 kb to 533 kb were detected. The viral community structure changed along the salinity gradient. Cluster analysis of the viral genome-banding pattern resulted in two main clusters. The virioplankton diversity within the samples with salinity from 40 per thousand to 150 per thousand was on the same cluster of a cladogram. The other group consisted of virioplankton from samples with salinity above 220 per thousand. The virioplankton diversity in the different samples was calculated using the Shannon index. The diversity index demonstrated an increase in diversity in the samples along the gradient from 40 per thousand to 150 per thousand salinity, followed by a decrease in the diversity index along the rest of the salinity gradient. These results demonstrate how viral diversity changes from habitats that are considered one of the most common (seawater) to habitats that are extreme in salt concentrations (saturated sodium brine). The diversity index was highest in the environments that lie in between the most extreme and the most common.     

Changes in riverine benthic diatom community structure along a chloride gradient

The application of salt is the primary means of deicing roads and highways in colder regions of north-eastern North America. This has increased the chloride concentrations of many lake and stream ecosystems. While this salinization has been documented, less is known about how increased salinity alters benthic communities in downstream ecosystems. Natural thresholds, at which there are large scale changes in community composition, have not yet been established for many types of contaminants, including chloride. The diatom community, which is sensitive to small changes in the ambient environment, has the potential to be a strong indicator of salinization effects on stream ecosystems. In this study, we sampled diatom communities in 41 streams across a salinity gradient throughout south central Ontario, Canada. We sampled benthic diatom assemblages in early May following complete snowmelt, when stream water chloride concentrations ranged from 5 to 502 mg/L. Based on redundancy analysis, we confirmed a strong association between the species composition of the diatom community and water conductivity, a commonly used index of stream salinity. Taxa indicator threshold analyses (TITAN) indicated the community changed substantially at chloride concentrations greater than 35 mg/L. We also found that, an indicator taxa, Meridion circulare, was extremely sensitive to high concentrations of salt and negatively correlated with chloride. In a wide synoptic survey of streams of our region, we found that streams in most developed watersheds exceed tolerance thresholds for benthic diatom communities. This work suggests that current chloride concentrations in urban watersheds are greatly exceeding the benthic community thresholds, for which improved management and regulatory practices are needed. Salinization thus appears to be an important feature of urban streams and needs to be considered as an important ecological driver in future studies.     

Differences in hyporheic-zone microbial community structure along a heavy-metal contamination gradient

The hyporheic zone of a river is nonphotic, has steep chemical and redox gradients, and has a heterotrophic food web based on the consumption of organic carbon entrained from downwelling surface water or from upwelling groundwater. The microbial communities in the hyporheic zone are an important component of these heterotrophic food webs and perform essential functions in lotic ecosystems. Using a suite of methods (denaturing gradient gel electrophoresis, 16S rRNA phylogeny, phospholipid fatty acid analysis, direct microscopic enumeration, and quantitative PCR), we compared the microbial communities inhabiting the hyporheic zone of six different river sites that encompass a wide range of sediment metal loads resulting from large base-metal mining activity in the region. There was no correlation between sediment metal content and the total hyporheic microbial biomass present within each site. However, microbial community structure showed a significant linear relationship with the sediment metal loads. The abundances of four phylogenetic groups (groups I, II, III, and IV) most closely related to alpha-, beta-, and gamma-proteobacteria and the cyanobacteria, respectively, were determined. The sediment metal content gradient was positively correlated with group III abundance and negatively correlated with group II abundance. No correlation was apparent with regard to group I or IV abundance. This is the first documentation of a relationship between fluvially deposited heavy-metal contamination and hyporheic microbial community structure. The information presented here may be useful in predicting long-term effects of heavy-metal contamination in streams and provides a basis for further studies of metal effects on hyporheic microbial communities.     

Macroinvertebrate colonization dynamics on artificial substrates along an algal resource gradient

Riparian canopy removal and land use may introduce multiple stressors that can alter food and habitat for stream organisms, but the influence of these alterations on macroinvertebrate colonization dynamics is less well known. A field study involving the simultaneous placement and removal of artificial substrates was performed to examine how macroinvertebrate colonization rates might vary with algal accumulation within a perennial stream segment in eastern Ohio, USA. The study was conducted over a 60-day summer colonization period in three reaches that were selected to represent an algal resource gradient according to canopy cover and agricultural nutrient sources in the riparian corridor. Total nitrogen, water temperatures, and mean algal biomass from substrates increased along the resource gradient represented by the study sites. Total macroinvertebrate biomass and the abundance and biomass of scrapers also increased according to the gradient. Correlation results indicated that chlorophyll a biomass, rather than time or temperature, was better related to the abundance and biomass of most primary consumers on substrates. These results suggest that the combined effects of elevated temperatures and nutrients can result in relatively rapid algal accrual that may alter the colonization and establishment of macroinvertebrate communities in streams subjected to gradients of riparian disturbances.     

Community structure of carrion flies along an island gradient

species richness, abundance relations, exploitation efficiencies, and population dynamics were examined within four carrion fly communities from a small isolated island in the Baltic to the large island of Åland. A total of 23 species and 11408 Specimens were collected.
Species richness (studied by rarefaction) of potential carrion flies was lowest on the small isolated island, but the smallest number of species emerged from the second largest island. Lucilia illustris Meig, was the most numerous species at every site, comprising 46–56% of the potential breeders and 71–91% of the emerging flies. Exploitation efficiency, measured by the numbers of individuals emerging per gram of carrion, was highest on the smallest island, but faunal similarity and ordination analyses suggest that competition was more intense on the larger islands.     

Zooplankton community structure along a trophic gradient in a canyon-shaped dam reservoir

The zooplankton community was surveyed along the longitudinalaxis of Rimov Reservoir (Czech Republic) on seven occasionsduring the vegetative season of 1996. The dimictic Rimov Reservoirhas a pronounced trophic gradient along its axis. In nearlyall samples, rotifers were dominant by numbers and formed onaverage 60–95% of the total zooplankton (including copepodnauplii). There was a consistent pattern of increasing relativeabundance of rotifers in the upper regions of the reservoircompared with the downstream parts. Very large rotifer populationscould develop in the upper regions, often associated with floodevents, but also coinciding with reduced abundance of crustaceansassociated with stronger wash-out effects and the advent ofturbid conditions. There was a greater similarity between twoadjacent sites in the proportions of crustacean species thanof rotifer species. This is partially due to the greater speciesdiversity of rotifers than of crustaceans. The timing of theseasonal succession of zooplankton species showed a coherentpattern along the whole longitudinal profile. The site-specificzooplankton patchiness seems to be reduced as there was no sitedependence if average data on zooplankton composition from downstreamlacustrine sites were compared.