Multi-scale variation in spatial heterogeneity for microbial community structure in an eastern Virginia agricultural field

To better understand the distribution of soil microbial communities at multiple spatial scales, a survey was conducted to examine the spatial organization of community structure in a wheat field in eastern Virginia (USA). Nearly 200 soil samples were collected at a variety of separation distances ranging from 2.5 cm to 11 m. Whole-community DNA was extracted from each sample, and community structure was compared using amplified fragment length polymorphism (AFLP) DNA fingerprinting. Relative similarity was calculated between each pair of samples and compared using geostatistical variogram analysis to study autocorrelation as a function of separation distance. Spatial autocorrelation was found at scales ranging from 30 cm to more than 6 m, depending on the sampling extent considered. In some locations, up to four different correlation length scales were detected. The presence of nested scales of variability suggests that the environmental factors regulating the development of the communities in this soil may operate at different scales. Kriging was used to generate maps of the spatial organization of communities across the plot, and the results demonstrated that bacterial distributions can be highly structured, even within a habitat that appears relatively homogeneous at the plot and field scale. Different subsets of the microbial community were distributed differently across the plot, and this is thought to be due to the variable response of individual populations to spatial heterogeneity associated with soil properties.     

Spatial characterization of arbuscular mycorrhizal fungal molecular diversity at the submetre scale in a temperate grassland

Although arbuscular mycorrhizal fungi (AMF) form spatially complex communities in terrestrial ecosystems, the scales at which this diversity manifests itself is poorly understood. This information is critical to the understanding of the role of AMF in plant community composition. We examined small-scale (submetre) variability of AMF community composition (terminal restriction fragment length polymorphism fingerprinting) and abundance (extraradical hyphal lengths) in two 1 m(2) plots situated in a native grassland ecosystem of western Montana. Extraradical AMF hyphal lengths varied greatly between samples (14-89 m g soil(-1)) and exhibited spatial structure at scales <30 cm. The composition of AMF communities was also found to exhibit significant spatial autocorrelation, with correlogram analyses suggesting patchiness at scales <50 cm. Supportive of overall AMF community composition analyses, individual AMF ribotypes corresponding to specific phylogenetic groups exhibited distinct spatial autocorrelation. Our results demonstrate that AMF diversity and abundance can be spatially structured at scales of <1 m. Such small-scale heterogeneity in the soil suggests that establishing seedlings may be exposed to very different, location dependent AMF communities. Our results also have direct implications for representative sampling of AMF communities in the field.     

Variation in Community Structure across Vertical Intertidal Stress Gradients: How Does It Compare with Horizontal Variation at Different Scales?

In rocky intertidal habitats, the pronounced increase in environmental stress from low to high elevations greatly affects community structure, that is, the combined measure of species identity and their relative abundance. Recent studies have shown that ecological variation also occurs along the coastline at a variety of spatial scales. Little is known, however, on how vertical variation compares with horizontal variation measured at increasing spatial scales (in terms of sampling interval). Because broad-scale processes can generate geographical patterns in community structure, we tested the hypothesis that vertical ecological variation is higher than fine-scale horizontal variation but lower than broad-scale horizontal variation. To test this prediction, we compared the variation in community structure across intertidal elevations on rocky shores of Helgoland Island with independent estimates of horizontal variation measured at the scale of patches (quadrats separated by 10s of cm), sites (quadrats separated by a few m), and shores (quadrats separated by 100s to 1000s of m). The multivariate analyses done on community structure supported our prediction. Specifically, vertical variation was significantly higher than patch- and site-scale horizontal variation but lower than shore-scale horizontal variation. Similar patterns were found for the variation in abundance of foundation taxa such as Fucus spp. and Mastocarpus stellatus, suggesting that the effects of these canopy-forming algae, known to function as ecosystem engineers, may explain part of the observed variability in community structure. Our findings suggest that broad-scale processes affecting species performance increase ecological variability relative to the pervasive fine-scale patchiness already described for marine coasts and the well known variation caused by vertical stress gradients. Our results also indicate that experimental research aiming to understand community structure on marine shores should benefit from applying a multi-scale approach.     

Detection of the horizontal spatial structure of soil fungal communities in a natural forest

Soil microbes are considered to be a key determinant of the aboveground plant community. They are not distributed uniformly in the environment, and their activity, abundance, and ecosystem functioning could vary across localities, characterized by high β-diversity. Investigating factors that contribute to high β-diversity can help infer the possible mechanisms of microbial community assembly, and predict the scale and extent of impacts that soil microbes have on the plant community. Because soil systems consist of multiple horizons (i.e., vertical stratification) associated with different soil properties, complete understanding of high β-diversity requires consideration of both horizontal and vertical spatial structures of soil microbial communities. We studied the community composition of soil fungi from the O- and A-horizons in a Castanopsis-dominated temperate forest, and compared horizontal spatial autocorrelation in species composition between the two soil horizons (O- versus A-horizons). Pyrosequencing analysis yielded 67,129 sequencing reads, summed across all the 48 forest soil samples. Clustering analysis resulted in 597 molecular operational taxonomic units (OTUs), 68 % of which were identified as fungi, represented by four phyla. The Mantel test revealed that the O-horizon communities are spatially clustered, and the observed high β-diversity was driven not only by changes in OTUs present, but also by high turnover in identities of OTUs in soil samples. Furthermore, Mantel correlogram analysis showed that the O-horizon communities resembled each other in composition within the range of 50 m, whereas the A-horizon communities lacked such horizontal autocorrelation. These differences in the scale patchiness could arise from two processes: (1) that environmental conditions could show higher heterogeneity in finer scale at the A-horizon than at the O-horizon; and/or (2) dispersal could be more frequent at the O-horizon than the A-horizon. The present study suggests that either environmental filtering (i.e., the niche-based process) or dispersal limitation (i.e., neutral process) could characterize the observed patterns of spatial clustering in the soil fungal community.     

Species turnover in ant assemblages is greater horizontally than vertically in the world's tallest tropical forest

Abiotic and biotic factors structure species assembly in ecosystems both horizontally and vertically. However, the way community composition changes along comparable horizontal and vertical distances in complex three‐dimensional habitats, and the factors driving these patterns, remains poorly understood. By sampling ant assemblages at comparable vertical and horizontal spatial scales in a tropical rainforest, we tested hypotheses that predicted differences in vertical and horizontal turnover explained by different drivers in vertical and horizontal space. These drivers included environmental filtering, such as microclimate (temperature, humidity, and photosynthetic photon flux density) and microhabitat connectivity (leaf area), which are structured differently across vertical and horizontal space. We found that both ant abundance and richness decreased significantly with increasing vertical height. Although the dissimilarity between ant assemblages increased with vertical distance, indicating a clear distance‐decay pattern, the dissimilarity was higher horizontally where it appeared independent of distance. The pronounced horizontal and vertical structuring of ant assemblages across short distances is likely explained by a combination of microclimate and microhabitat connectivity. Our results demonstrate the importance of considering three‐dimensional spatial variation in local assemblages and reveal how highly diverse communities can be supported by complex habitats.     

Dormant propagule banks integrate spatio-temporal heterogeneity in cladoceran communities

The dynamics of populations of short-lived organisms are very patchy, both in space and time. The production of dormant propagules, however, results in an effective increase in generation time. We hypothesize that prolonged dormancy, together with variable regeneration niches, result in integration of temporal variability in community structure. In addition, in aquatic habitats, mechanisms such as sediment focussing can contribute to the integration of spatial variability. We tested the hypothesis that dormant propagule banks integrate spatial and temporal variation in active zooplankton communities. This was done by comparing cladoceran species richness and the community structure of hatchling assemblages retrieved from propagule bank samples collected on a single occasion with assemblages encountered in active community samples covering spatial variation (littoral and pelagic zone), diel (day and night), intra-year (May–October) and inter-year variation (1996–2000). The egg bank community structure differed significantly from the active community structure, but the dissimilarity decreased as spatial and temporal variation was better covered by the active community samples. Furthermore, the identification of all fully grown hatchlings (n=214) yielded an equally high number of species (n=22) to that occurring in all active community samples together (a total of 1,730 individuals were analysed). We conclude that the analysis of dormant propagules may form a cost-efficient alternative tool to the analysis of active community samples for an integrated assessment of cladoceran communities.     

Resource heterogeneity in oldfields

Abstract. Spatial heterogeneity of photosynthetically active radiation (PAR), soil moisture and soil N mineralization in a range of oldfield communities was analyzed using semi-variograms for transect data. Percent transmittance of PAR was examined in eight communities, and soil moisture and N mineralization were examined in the two most common communities. In general, the sites with the highest resource availability had the smallest coefficients of variation. For light, 63% of the transects showed significant non-zero spatial autocorrelation with sills at 1 - 70 cm distance intervals. Although the grass-dominated communities had the highest average PAR levels and the lowest coefficients of variation, they also were among those with the greatest percentage of transects that had non-zero spatial autocorrelation. For light, the average semivariogram range, or distance within which samples were autocorrelated, was 19 cm and different among communities at p = 0.07. For soil moisture, two of three shrub sites and one of three grass sites showed non-zero spatial autocorrelation with sills at 10 - 300 cm distance intervals. Average semivariance range was 249 cm for the shrub community and 170 cm for the grass community. For N-mineralization, none of the shrub and one of three grass sites showed non-zero spatial autocorrelation with a sill, with a semivariance range of 60 cm. Soil moisture and N-mineralization were higher in the shrub than in the grass communities. Overall, these results indicate that resource variability occurred within patches of uniform vegetation, and the range of resource spatial dependence was different among resources even within a single community type. Our results suggest that different seedlings invading these communities will experience very different patterns of microsite heterogeneity as a result of their specific resource requirements.     

Small-scale spatial heterogeneity of arbuscular mycorrhizal fungal abundance and community composition in a wetland plant community

Although it has become increasingly clear that arbuscular mycorrhizal fungi (AMF) play important roles in population, community, and ecosystem ecology, there is limited information on the spatial structure of the community composition of AMF in the field. We assessed small-scale spatial variation in the abundance and molecular diversity of AMF in a calcareous fen, where strong underlying environmental gradients such as depth to water table may influence AMF. Throughout an intensively sampled 2 × 2 m plot, we assessed AMF inoculum potential at a depth of 0–6 and 6–12 cm and molecular diversity of the AMF community using terminal restriction fragment length polymorphism of 18S rDNA. Inoculum potential was only significantly spatially autocorrelated at a depth of 6–12 cm and was significantly positively correlated with depth to water table at both depths. Molecular diversity of the AMF community was highly variable within the plot, ranging from 2–14 terminal restriction fragments (T-RFs) per core, but the number of T-RFs did not relate to water table or plant species richness. Plant community composition was spatially autocorrelated at small scales, but AMF community composition showed no significant spatial autocorrelation. Saturated soils of calcareous fens contain many infective AMF propagules and the abundance and diversity of AMF inoculum is patchy over small spatial scales. An erratum to this article can be found at     

Spatial scaling and transition in pneumatophore arthropod communities

Although most ecological variables are scale-dependent, few studies cover a broad range of spatial scales. Here, we consider South African mangrove pneumatophore arthropod communities (mites, crustaceans and insects), across seven spatial scales (from 10  cm to 100  km). We plot spatial autocorrelation in individual species, evaluate if resource and habitat availability determine spatial patterning, and identify the scales of community transition. Spatial autocorrelation in most ecological variables decreased with increasing spatial scale, with notable exceptions for the larger scales. Negative abundance autocorrelation was stronger at 10  km than at 100  km for common species, while the opposite was true for rare species. Spatial autocorrelation in species richness decreased from 1  m (strong positive) to 10  km (strong negative), but was not significant at the 100  km scale. These patterns reflect the patchy distribution of pneumatophores within mangrove forests, that of the forests along the coast, and the poor dispersal abilities of most of the arthropods sampled, in a highly dynamic environment. Although resource and habitat availability exhibited a similar autocorrelation pattern to that of the community, the total mass of pneumatophores did not appear to be an important determinant of community structure. Variations in the abundance of common species, as well as the restricted distribution of rare species caused assemblage structure to change gradually with increasing distance from 10 cm to 100 km, but only marginally from 10 to 100  km. We highlight the need for cross-scale studies in bridging the gap between two key ecological concepts: potential ecological niche and realized geographic range.     

青藏高原淡水湖普莫雍错和盐水湖阿翁错湖底沉积物中细菌群落的垂直分布

【目的】湖泊沉积物中存储着大量独特的微生物,这些微生物在湖泊生态系统生物地球化学循环中扮演着非常重要的角色。然而,很少有研究报道微生物群落在湖泊沉积物中的垂直分布。本文比较研究青藏高原淡水湖普莫雍错和盐水湖阿翁错沉积物在不同深度下细菌的丰度和群落结构。【方法】利用定量PCR(q PCR)和变性梯度凝胶电泳(DGGE)技术分别测定细菌群落的丰度与群落结构。【结果】定量PCR结果显示,湖泊沉积物中细菌丰度均随深度增加而降低,盐水湖阿翁错和淡水湖普莫雍错的细菌丰度分别从1011数量级降到108数量级,从1012数量级降到1010数量级。在相对应的沉积物层,淡水湖沉积物的细菌丰度比盐水湖高1-2个数量级。变性梯度凝胶电泳(DGGE)指纹图谱的分析表明,淡水湖沉积物细菌群落的DGGE条带数(丰富度)显著高于盐水湖(P=0.014);淡水与盐水湖泊沉积物细菌群落结构明显不同,同时在同一湖泊沉积物中上层(0-6 cm)和下层(7-20 cm)细菌群落结构也呈明显分异。系统发育分析表明,盐水湖阿翁错沉积物特有菌门为Gamma-变形菌、拟杆菌门、蓝细菌和栖热菌门,而淡水湖普莫雍错沉积物中特有菌门为Delta-和Beta-变形菌、酸杆菌和绿弯菌门。【结论】青藏高原淡水与盐水湖泊沉积物细菌丰度与群落结构具有明显的差异;同时,细菌群落结构在沉积物的不同深度也表现出差异。这些结果可为进一步阐明青藏高原湖泊生态系统中微生物对气候环境变化的响应提供科学依据。     

三江平原农田土壤跳虫多尺度空间自相关性

土壤动物多尺度空间自相关性特征是土壤动物空间异质性和空间共存格局研究的重要基础。以土壤跳虫为研究对象,以中国科学院三江平原沼泽湿地生态实验站为研究区,于2011年8月和10月,选取具30 a以上耕作历史的旱地为实验样地,以5 m为步长设置一个50 m×50 m的实验样地,采用地统计中的全局Moran's I指数和局部Moran's I指数相结合的方法,研究土壤跳虫多尺度空间自相关性特征。全局空间自相关结果表明,土壤跳虫群落总密度和多数跳虫种类存在显著的多尺度空间自相关特征,多数为显著的正的空间自相关性,形成明显的空间集群。局部空间自相关结果表明,土壤跳虫群落总密度和所有跳虫种类均存在显著的局部空间自相关性,在局部地区形成"高—高"和/或"低—低"的空间集群,并和"高—低"和/或"低—高"的空间孤立区相伴发生,即形成"斑块"和"孔隙"相间分布的水平镶嵌格局;这种镶嵌格局具一定的时间动态特征,从夏季到秋季斑块大小和空间分布范围略有变化。研究表明,土壤跳虫具有明显的多尺度空间自相关性;空间集群是土壤跳虫的常见空间分布格局,在样地内形成"斑块"和"孔隙"相间分布的水平镶嵌格局,这种格局具年内时间变异性。     

Bacterial water quality and network hydraulic characteristics: a field study of a small, looped water distribution system using culture-independent molecular methods

Aims: To determine the spatial and temporal variability in the abundance, structure and composition of planktonic bacterial assemblages sampled from a small, looped water distribution system and to interpret results with respect to hydraulic conditions. Methods and Results: Water samples were collected from five sampling points, twice a day at 06:00 h and 09:00 h on a Monday (following low weekend demand) and a Wednesday (higher midweek demand). All samples were fully compliant with current regulated parameter standards. This study did not show obvious changes in bacterial abundance (DAPI count) or community structure Denaturing gradient gel electrophoresis analysis with respect to sample site and hence to water age; however, the study did show temporal variability with respect to both sampling day and sample times. Conclusions: Data suggests that variations in the bacterial assemblages may be associated with the local system hydraulics: the bacterial composition and numbers, over short durations, are governed by the interaction of the bulk water and the biofilm influenced by the hydraulic conditions. Significance and Impact of the Study: This study demonstrates general stability in bacterial abundance, community structure and composition within the system studied. Trends and patterns supporting the transfer of idealized understanding to the real world were evident. Ultimately, such work will help to safeguard potable water quality, fundamental to public health.     

Stream community structure in relation to spatial variation: the influence of mesohabitat characteristics

Community structure of benthic macroinvertebrates was studied in six first- through fourth-order streams in northeast France, to elucidate changes in richness, abundance, diversity and evenness of mesohabitat assemblages as a function of environmental conditions. Patch samples were subjected to multivariate analyses to determine: (i) relationships among seven indices describing community structure (structure parameters); (ii) relationships among seven environmental variables; (iii) the relationship between community structure and environmental characteristics of patches. Faunal data showed that indices measuring the distribution of individuals among taxa (evenness, dominance) and richness are prominent in describing the structure of macroinvertebrate communities of mesohabitats. The analysis of environmental data demonstrated a major differentiating ability of current velocity and strong inter-relations among in-stream hydraulic-dependent parameters in structuring the mesohabitat environment. The co-structure (= relationship) between community organization and environmental variables indicated that substrate may be a primary determinant of community structure. Current velocity and water depth emerged as secondary factors. Trends in community structure were closely related to the spatial variability of mesohabitats. Species richness increased with habitat heterogeneity. Total abundance increased with trophic potentialities of patches. Equitability and diversity seemed to increase with patch stability. This revised version was published online in July 2006 with corrections to the Cover Date.     

Species Richness,Spatial Variation,and Abundance of the Soil Seed Bank of a Secondary Tropical Rain Forest1

Despite the importance of the soil seed bank in tropical forest regeneration, little is known about spatial variability in species composition and abundance of seeds stored in the soil. To develop sampling methods for comparative studies, we examined species richness, spatial variation, and abundance of germinants from the soil seed bank in a 16 year old secondary, tropical wet forest at La Selva Biological Station, Costa Rica. Surface soil (10 cm deep, 4.7 cm diameter) was collected at the intersection points of a gridded 1 ha plot (10 × 10-m grid, 121 samples) and in a nested 100 m² subplot (2 × 2-m grid, 36 samples). The 1 ha plot had a density of 4535 seeds/m² with 34 species observed. Based on a series of 100 randomized species accumulation curves, a Michaelis-Menten fit predicted a mean species richness of 36.3 species; the number of observed species was close to the predicted asymptote. A nonparametric, first-order jackknife species richness estimator predicted a species richness of 37.0 species. Eighty-five and 95 percent of the observed species richness is contained, on average, within 41 and 74 pooled samples, respectively. Within the 100 m² nested subplot, a density of 5476 seeds/m² was observed, comprising 26 species with an estimated species richness (Michaelis-Menten fit) of 29.1 species. The jackknife species richness estimator predicted a species richness of 36.7 species. For species richness and abundance of both plots, spatial autocorrelation statistics (Moran's I) were not significantly different from zero at lag distances from 2 to 100 m, indicating a random distribution at these spatial scales. For this site, accurate estimates of species composition depend upon the number of samples collected as well as the spatial distribution of sampling effort. Many small samples distributed over a large area provide greater accuracy and precision for estimating species richness of the soil seed bank.     

Spatial distribution of bacterivorous nematodes in a Chinese Ecosystem Research Network (CERN) site

Geostatistics was applied to assess the spatial distribution of bacterivorous nematodes in a Chinese Ecosystem Research Network (CERN) site in northeast China. A 42×30 m plot was divided into grids with 7×5 m spacing that included 49 sampling points. Soil samples were collected from depths of 0–10 cm and 10–20 cm. The results showed that Cephalobus and Panagrolaimus were the most dominant bacterivores, which together represented 74 and 82% of total bacterivorous nematodes on average at depths of 0–10 cm and 10–20 cm, respectively. Within-site variability was high for these nematode genera. Geostatistical analysis indicated that a major part of this variability was spatially dependent; variograms suggest that 55–100% of sample population variance was related to spatial autocorrelation over ranges of 9–91 m. The mean numbers of total bacterivores and Panagrolaimus populations were higher at 0–10 cm depth than at 10–20 cm depth. Between the two depths, different distribution patterns were found for Panagrolaimus, whereas similar patterns were found for Cephalobus. The maps obtained by kriging well illustrated horizontal distribution patterns of bacterivorous nematodes at two depths at field scale.     

Seed bank spatial structure in semi-arid environments: beyond the patch-bare area dichotomy

The prevalence of patchy structures in vegetation is a common feature in semi-arid ecosystems. Although the effect of patches on seed density is widely known, we still lack information on how patch features affect seed bank density and composition. Our aim was to answer two basic questions: (1) How do seed bank density and composition vary within and outside patch aboveground physical limits? and (2) Do patch characteristics affect soil seed bank density and composition? We sampled 50 shrub patches in a semi-arid gypsum system in Central Spain, measuring patch size, composition and structure, and seed bank at three locations per shrub (centre, edge and outside). We calculated the effect of interior patch location, patch composition and structure on seed density and composition. Patches acted both as seed sources, increasing seed density in neighbouring areas and as seed sinks by trapping seeds from bare areas. Patch structure (erect perennial cover) had the greatest effect on seed bank density, whereas patch size and microslope had the greatest influence on bare area density. Patch structure, composition and interior location explained the variation in seed bank composition. Patch effect extends to the surrounding bare matrix creating a seed bank gradient in density and composition. This effect is modulated by patch structure and composition and affects seed bank composition. Our results suggest that the spatial structure of gypsum community seed banks may act as a mechanism for a spatial storage effect contributing to the maintenance of high levels of diversity in semi-arid environments     

塔河源荒漠河岸林群落物种组成、结构与植物区系特征

为了更好地了解荒漠河岸林植被动态与生物多样性维持机制,于塔里木河干流源头荒漠河岸林内建立6个1 hm 2样地,对群落物种组成、数量特征和空间格局等进行综合分析。结果表明,塔河源荒漠河岸林群落结构简单、物种多样性低,共有物种12科15属16种,杨柳科重要值最大(28. 97%),是群落优势建群科。取样面积在0. 04 hm 2时,包括了87. 5%的物种;样地内稀有种和偶见种均占所有物种的12. 5%。植物区系贫乏,单种科、属多,温带成分占绝对优势,古地中海成分也占有重要地位,具典型温带区系性质。样地内 DBH ≥ 1 cm 的活木本个体有2497株,灰胡杨多度占92. 95%,胸高断面积和重要值最大,在群落中占绝对优势地位。群落内科、属、种的数量随植株高度级的增加而减少,垂直结构层次分明,由乔木层、灌木层和草本层构成。样地内所有树种平均胸径15. 57 cm,径级与高度级结构均呈偏正态分布,缺乏高度≤ 2 m的个体,群落更新不良。优势种灰胡杨、胡杨径级结构均呈单峰型,其中胡杨幼树出现断层,灰胡杨幼苗向幼树发展过程中死亡率极高(92. 56%),均为衰退型种群。两个优势种空间格局呈聚集分布,不同生境下随径级增大空间分布格局变化不同;且两个优势种在空间上相互排斥而占据不同生境,暗示着种间竞争与生境异质性是影响荒漠河岸林物种空间分布格局和物种共存的重要因素。     

中亚热带南酸枣落叶阔叶林土壤磷素空间变异及其影响因素

在湖南省长沙县大山冲国有林场南酸枣落叶阔叶林建立1 hm²固定样地,基于植物群落学调查数据和等距离网格布点取样的土壤养分测定数据,采用地统计学和GIS相结合的方法,研究土壤P含量的空间变异特征及其影响因子.结果表明: 腐殖质层及0～10、10～20、20～30 cm土层的全P、有效P含量的均为中等强度变异,同一土层有效P含量的变异程度较全P含量高,随着土壤深度增加,全P、有效P含量下降,变异程度增大.土壤全P、有效P含量具有较高的空间自相关性,主要受结构性因素影响.有效P含量的空间异质性较全P强,各土层全P、有效P含量空间自相关范围分别为92.80～168.90 m、79.43～106.20 m.同一土层全P含量分维数高于有效P,空间格局较有效P复杂,有效P含量空间依赖性更强,具有更好的结构性.腐殖质层及0～10、10～20、20～30 cm土层的全P、有效P含量呈现条带状和斑块状梯度性分布,且全P、有效P含量的空间变化趋势基本一致,高值出现在洼地,低值则出现在山脊.全P、有效P含量与高程、地表凋落物现存量呈显著负相关,与凹凸度、树种种数、株数、土壤pH相关性不显著,与土壤有机C、全N含量呈显著正相关.这反映出土壤P的淋溶特性,其空间变异性受到多种因子相互作用的影响.     

Fine-scale spatial patterns in bacterial community composition and function within freshwater ponds

The extent to which non-host-associated bacterial communities exhibit small-scale biogeographic patterns in their distribution remains unclear. Our investigation of biogeography in bacterial community composition and function compared samples collected across a smaller spatial scale than most previous studies conducted in freshwater. Using a grid-based sampling design, we abstracted 100+ samples located between 3.5 and 60 m apart within each of three alpine ponds. For every sample, variability in bacterial community composition was monitored using a DNA-fingerprinting methodology (automated ribosomal intergenic spacer analysis) whereas differences in bacterial community function (that is, carbon substrate utilisation patterns) were recorded from Biolog Ecoplates. The exact spatial position and dominant physicochemical conditions (for example, pH and temperature) were simultaneously recorded for each sample location. We assessed spatial differences in bacterial community composition and function within each pond and found that, on average, community composition or function differed significantly when comparing samples located >20 m apart within any pond. Variance partitioning revealed that purely spatial variation accounted for more of the observed variability in both bacterial community composition and function (range: 24–38% and 17–39%) than the combination of purely environmental variation and spatially structured environmental variation (range: 17–32% and 15–20%). Clear spatial patterns in bacterial community composition, but not function were observed within ponds. We therefore suggest that some of the observed variation in bacterial community composition is functionally ‘redundant''. We confirm that distinct bacterial communities are present across unexpectedly small spatial scales suggesting that populations separated by distances of >20 m may be dispersal limited, even within the highly continuous environment of lentic water.     

Spatial and temporal variability among marine Bacteroidetes populations in the NW Mediterranean Sea

The abundance and structure of Bacteroidetes populations at diverse temporal and spatial scales were investigated in the Northwestern Mediterranean Sea. At a temporal scale, their relative abundance exhibited a marked seasonality, since it was higher in spring and decreased in winter. Similarly, Bacteroidetes community structure encompassed three main groups (winter, spring and summer-fall), which mimicked global bacterioplankton seasonality. At the spatial scale, relative abundances were similar in all surface samples along an inshore–offshore transect, but they decreased with depth. Analysis of the community structure identified four markedly different groups mostly related to different depths. Interestingly, seasonal changes in abundance and community structure were not synchronized. Furthermore, richness was higher when Bacteroidetes were less abundant. The variability of Bacteroidetes contributions to community structure in the temporal and spatial scales was correlated with different environmental factors: day length was the most important factor at the temporal scale, and salinity at the spatial scale. The community composition in terms of phylotypes changed significantly over time and along the depth gradients, but season or depth-specific phylogenetic clusters were not identified. Delineation of coherent Bacteroidetes sub-clusters should help to uncover higher resolution patterns within Bacteroidetes, and explore associations with environmental and biological variables.