Microbial communities across nearshore to offshore coastal transects are primarily shaped by distance and temperature

Recent studies have focused on linking marine microbial communities with environmental factors, yet, relatively little is known about the drivers of microbial community patterns across the complex gradients from the nearshore to open ocean. Here, we examine microbial dynamics in 15 five-station transects beginning at the estuarine Piver's Island Coastal Observatory (PICO) time-series site and continuing 87 km across the continental shelf to the oligotrophic waters of the Sargasso Sea. 16S rRNA gene libraries reveal strong clustering by sampling site with distinct nearshore, continental shelf and offshore oceanic communities. Water temperature and distance from shore (which serves as a proxy for gradients in factors such as productivity, terrestrial input and nutrients) both most influence community composition. However, at the phylotype level, modelling shows the distribution of some taxa is linked to temperature, others to distance from shore and some by both factors, highlighting that taxa with distinct environmental preferences underlie apparent clustering by station. Thus, continental margins contain microbial communities that are distinct from those of either the nearshore or the offshore environments and contain mixtures of phylotypes with nearshore or offshore preferences rather than those unique to the shelf environment.     

Spatial scale impacts microbial community composition and distribution within and across stream ecosystems in North and Central America

A mechanistic understanding of factors that structure spatiotemporal community composition is a major challenge in microbial ecology. Our study of microbial communities in the headwaters of three freshwater stream networks showed significant community changes at the small spatial scale of benthic habitats when compared to changes at mid- and large-spatial scales associated with stream order and catchment. Catchment (which included temperate and tropical catchments) had the strongest influence on community composition followed by habitat type (epipsammon or epilithon) and stream orders. Alpha diversity of benthic microbiomes resulted from interactions between catchment, habitat, and canopy. Epilithon contained relatively more Cyanobacteria and algae while Acidobacteria and Actinobacteria proportions were higher in epipsammic habitats. Turnover from replacement created ~60%–95% of beta diversity differences among habitats, stream orders, and catchments. Turnover within a habitat type generally decreased downstream indicating longitudinal linkages in stream networks while between habitat turnover also shaped benthic microbial community assembly. Our study suggests that factors influencing microbial community composition shift in dominance across spatial scales, with habitat dominating locally and catchment dominating globally.     

Partitioning of beta‐diversity reveals distinct assembly mechanisms of plant and soil microbial communities in response to nitrogen enrichment

Nitrogen (N) deposition poses a serious threat to terrestrial biodiversity and alters plant and soil microbial community composition. Species turnover and nestedness reflect the underlying mechanisms of variations in community composition. However, it remains unclear how species turnover and nestedness contribute to different responses of taxonomic groups (plants and soil microbes) to N enrichment. Here, based on a 13‐year consecutive multi‐level N addition experiment in a semiarid steppe, we partitioned community β‐diversity into species turnover and nestedness components and explored how and why plant and microbial communities reorganize via these two processes following N enrichment. We found that plant, soil bacterial, and fungal β‐diversity increased, but their two components showed different patterns with increasing N input. Plant β‐diversity was mainly driven by species turnover under lower N input but by nestedness under higher N input, which may be due to a reduction in forb species, with low tolerance to soil Mn²⁺, with increasing N input. However, turnover was the main contributor to differences in soil bacterial and fungal communities with increasing N input, indicating the phenomenon of microbial taxa replacement. The turnover of bacteria increased greatly whereas that of fungi remained within a narrow range with increasing N input. We further found that the increased soil Mn²⁺ concentration was the best predictor for increasing nestedness of plant communities under higher N input, whereas increasing N availability and acidification together contributed to the turnover of bacterial communities. However, environmental factors could explain neither fungal turnover nor nestedness. Our findings reflect two different pathways of community changes in plants, soil bacteria, and fungi, as well as their distinct community assembly in response to N enrichment. Disentangling the turnover and nestedness of plant and microbial β‐diversity would have important implications for understanding plant–soil microbe interactions and seeking conservation strategies for maintaining regional diversity.     

若尔盖高原泥炭沼泽湿地土壤细菌群落空间分布及其驱动机制

了解高原泥炭沼泽湿地生态系统土壤微生物群落结构组成、多样性及空间分布特征对认识高原湿地生态特征及演化过程至关重要。利用高通量测序技术,在局域尺度上研究了四川若尔盖高原泥炭沼泽湿地土壤细菌群落结构与多样性特征。通过进一步测定土壤及植物基本理化指标,量化采样点之间的地理距离,比较了细菌群落不同成员（稀有种和丰富种）的空间周转差异,分析了土壤环境变量和空间因子对细菌群落结构的相对贡献。结果表明：若尔盖泥炭土壤细菌群落主要由绿弯菌门（Chloroflexi）（26.25%）、变形菌门（Proteobacteria）（23.21%）、厚壁菌门（Firmicutes）（10.56%）等优势物种门类组成;土壤细菌群落结构表现出较强的空间依赖关系,群落结构相似性随采样点地理距离增加而逐渐降低,细菌群落的周转速率表现为总细菌群落 > 丰富种 > 稀有种;Mantel检验结果显示,地上生物量与细菌群落呈极显著相关性（P<0.01）,其中,影响稀有种空间分布特征的环境因子还包括土壤硫含量、活性磷、Mn和土壤pH值;方差分解分析表明,局域尺度上的土壤因子对若尔盖高原泥炭沼泽土壤细菌群落构建的相对贡献大于空间因子,土壤异质性是影响微生物空间分布特征的关键因素。研究为开展高原湿地泥炭土壤微生物多样性调查及揭示微生物群落构建机制提供了重要参考。     

黄土丘陵沟壑区地形变化对土壤微生物群落功能多样性的影响

研究黄土高原丘陵沟壑区破碎地形对土壤微生物功能多样性的影响,对于理解复杂地形区生态过程与系统功能的空间变化具有重要意义。选择陕西省安塞县陈家洼为研究区,依据坡面地形变化选择不同坡位土壤,采用Biolog微平板培养法探究地形变化对土壤微生物群落功能多样性的影响。实验发现,土壤微生物群落培养的平均颜色变化率(AWCD)增长曲线总的呈现出坡下部坡中部坡上部的规律,且坡下部AWCD值与坡中部、坡上部间差异显著(P0.05);坡下部土壤微生物群落功能多样性显著高于坡中部和坡上部,但不同土层深度(0—10 cm、10—20 cm)间无显著性差异(P0.05);对土壤微生物群落功能多样性差异贡献较大的碳源是糖类、羧酸类和多酚化合物类碳源;土壤含水率高低是不同坡位土壤微生物群落功能多样性差异显著的主要原因;微生物群落丰富度(H)和均一度(D)与土壤全氮含量正相关,优势度(U)反之,土壤全碳、全磷和p H对土壤微生物群落结构和功能多样性差异作用不显著。     

Microbial community changes in methanogenic granules during the transition from mesophilic to thermophilic conditions

Upflow anaerobic sludge blanket (UASB) reactor is one of the most applied technologies for various high-strength wastewater treatments. The present study analysed the microbial community changes in UASB granules during the transition from mesophilic to thermophilic conditions. Dynamicity of microbial community in granules was analysed using high-throughput sequencing of 16S ribosomal RNA gene amplicons, and the results showed that the temperature strictly determines the diversity of the microbial consortium. It was demonstrated that most of the microbes which were present in the initial mesophilic community were not found in the granules after the transition to thermophilic conditions. More specifically, only members from family Anaerolinaceae managed to tolerate the temperature change and contributed in maintaining the physical integrity of granular structure. On the contrary, new hydrolytic and fermentative bacteria were quickly replacing the old members in the community. A direct result from this abrupt change in the microbial diversity was the accumulation of volatile fatty acids and the concomitant pH drop in the reactor inhibiting the overall anaerobic digestion process. Nevertheless, by maintaining deliberately the pH levels at values higher than 6.5, a methanogen belonging to Methanoculleus genus emerged in the community enhancing the methane production.

     

The Pareto principle: To what extent does it apply to resource acquisition in stable microbial communities and thereby steer their geno−/ecotype compositions and interactions between their members?

The Pareto principle, or 20:80 rule, describes resource distribution in stable communities whereby 20% of community members acquire 80% of a key resource. In this Burning Question, we ask to what extent the Pareto principle applies to the acquisition of limiting resources in stable microbial communities; how it may contribute to our understanding of microbial interactions, microbial community exploration of evolutionary space, and microbial community dysbiosis; and whether it can serve as a benchmark of microbial community stability and functional optimality?     

Microbial diversity in acid mineral bioleaching systems of dongxiang copper mine and Yinshan lead–zinc mine

To understand the composition and structure of microbial communities in acid mineral bioleaching systems, the molecular diversity of 16S rDNA genes was examined using a PCR-based cloning approach. A total of 31 Operational Taxonomic Units (OTUs) were obtained from the four samples taken from four different bioleaching sites in Yinshan lead–zinc mine and Dongxiang copper mine in Jiangxi Province, China. The percentages of overlapping OTUs between sites ranged from 22.2 to 50.0%. Phylogenetic analysis revealed that the bacteria present at the four bioleaching sites fell into six divisions, α-Proteobacteria (1.1%), β-Proteobacteria (2.3%), γ-Proteobacteria (30.8%), Firmicutes (15.4%), Actinobacteria (0.3%) and Nitrospira (50.1%). Organisms of genera Leptospirillum, Acidithiobacillus, and Sulfobacillus, which were in Nitrospira, γ-Proteobacteria, and Firmicutes divisions, respectively, were the most dominant. The results of principal component analysis based on the six phylogenetic divisions and biogeochemical data indicated that the microbial community structure of a site was directly related to the biogeochemical characteristic of that site. It follows therefore that sites with similar biogeochemical characteristics were comprised of similar microbial community structures. The results in our study also suggest that the elements copper and arsenic appear to be the key factors affecting the compositions and structures of microbial community in the four bioleaching sites. Zhiguo He, Shengmu Xiao, Xuehui Xie are equally contributed to this work.     

Fungal-Fungal Associations Affect the Assembly of Endophyte Communities in Maize (Zea mays)

Many factors can affect the assembly of communities, ranging from species pools to habitat effects to interspecific interactions. In microbial communities, the predominant focus has been on the well-touted ability of microbes to disperse and the environment acting as a selective filter to determine which species are present. In this study, we investigated the role of biotic interactions (e.g., competition, facilitation) in fungal endophyte community assembly by examining endophyte species co-occurrences within communities using null models. We used recombinant inbred lines (genotypes) of maize (Zea mays) to examine community assembly at multiple habitat levels, at the individual plant and host genotype levels. Both culture-dependent and culture-independent approaches were used to assess endophyte communities. Communities were analyzed using the complete fungal operational taxonomic unit (OTU) dataset or only the dominant (most abundant) OTUs in order to ascertain whether species co-occurrences were different for dominant members compared to when all members were included. In the culture-dependent approach, we found that for both datasets, OTUs co-occurred on maize genotypes more frequently than expected under the null model of random species co-occurrences. In the culture-independent approach, we found that OTUs negatively co-occurred at the individual plant level but were not significantly different from random at the genotype level for either the dominant or complete datasets. Our results showed that interspecific interactions can affect endophyte community assembly, but the effects can be complex and depend on host habitat level. To our knowledge, this is the first study to examine endophyte community assembly in the same host species at multiple habitat levels. Understanding the processes and mechanisms that shape microbial communities will provide important insights into microbial community structure and the maintenance of microbial biodiversity.     

青藏高原高寒草甸不同海拔梯度下土壤微生物群落碳代谢多样性

土壤微生物群落功能多样性对维持生态系统功能和稳定性具有非常重要的意义。为探究青藏高原高寒草甸不同海拔梯度下土壤微生物碳源利用差异以及影响机制,运用Biolog微平板技术,研究了西藏当雄县草原站4300—5100 m的6个不同海拔梯度下土壤微生物群落碳源代谢多样性。研究结果表明:(1)不同海拔下高寒草甸土壤微生物碳源的利用程度均随培养时间的延长而升高;微生物代谢活性和群落多样性指数均随海拔升高呈现先上升后下降的单峰变化趋势,整体表现4800 m4950 m4400 m4650 m5100 m4300 m;(2)主成分分析表明不同海拔显著影响了土壤微生物群落碳源代谢多样性,其中碳水化合物类、氨基酸类和胺类碳源是各海拔土壤微生物的偏好碳源;碳水化合物类、羧酸类、氨基酸类和胺类碳源的利用强度受海拔影响较大;(3)分类变异分析表明,土壤、植物和气候因素是影响不同海拔碳源利用变异的主要影响因子,可解释不同海拔的碳源利用差异的79.0%;排除环境因子之间的多重及交互作用,偏曼特尔检验表明土壤含水量、植被丰富度和年均降水量是影响不同海拔微生物碳源利用多样性的最重要的环境因子。综上,研究表明青藏高寒草甸不同海拔土壤微生物碳源代谢多样性呈现显著的海拔差异趋势,其海拔差异主要受到土壤含水量、植被丰富度和年均降水量的影响。     

The Adult Cystic Fibrosis Airway Microbiota Is Stable over Time and Infection Type,and Highly Resilient to Antibiotic Treatment of Exacerbations

Cystic fibrosis (CF) is characterized by defective mucociliary clearance and chronic airway infection by a complex microbiota. Infection, persistent inflammation and periodic episodes of acute pulmonary exacerbation contribute to an irreversible decline in CF lung function. While the factors leading to acute exacerbations are poorly understood, antibiotic treatment can temporarily resolve pulmonary symptoms and partially restore lung function. Previous studies indicated that exacerbations may be associated with changes in microbial densities and the acquisition of new microbial species. Given the complexity of the CF microbiota, we applied massively parallel pyrosequencing to identify changes in airway microbial community structure in 23 adult CF patients during acute pulmonary exacerbation, after antibiotic treatment and during periods of stable disease. Over 350,000 sequences were generated, representing nearly 170 distinct microbial taxa. Approximately 60% of sequences obtained were from the recognized CF pathogens Pseudomonas and Burkholderia, which were detected in largely non-overlapping patient subsets. In contrast, other taxa including Prevotella, Streptococcus, Rothia and Veillonella were abundant in nearly all patient samples. Although antibiotic treatment was associated with a small decrease in species richness, there was minimal change in overall microbial community structure. Furthermore, microbial community composition was highly similar in patients during an exacerbation and when clinically stable, suggesting that exacerbations may represent intrapulmonary spread of infection rather than a change in microbial community composition. Mouthwash samples, obtained from a subset of patients, showed a nearly identical distribution of taxa as expectorated sputum, indicating that aspiration may contribute to colonization of the lower airways. Finally, we observed a strong correlation between low species richness and poor lung function. Taken together, these results indicate that the adult CF lung microbiome is largely stable through periods of exacerbation and antibiotic treatment and that short-term compositional changes in the airway microbiota do not account for CF pulmonary exacerbations.     

Rewiring of peatland plant–microbe networks outpaces species turnover

Enviro–climatic changes are thought to be causing alterations in ecosystem processes through shifts in plant and microbial communities; however, how links between plant and microbial communities change with enviro–climatic change is likely to be less straightforward but may be fundamental for many ecological processes. To address this, we assessed the composition of the plant community and the prokaryotic community – using amplicon-based sequencing – of three European peatlands that were distinct in enviro–climatic conditions. Bipartite networks were used to construct site-specific plant–prokaryote co-occurrence networks. Our data show that between sites, plant and prokaryotic communities differ and that turnover in interactions between the communities was complex. Essentially, turnover in plant–microbial interactions is much faster than turnover in the respective communities. Our findings suggest that network rewiring does largely result from novel or different interactions between species common to all realised networks. Hence, turnover in network composition is largely driven by the establishment of new interactions between a core community of plants and microorganisms that are shared among all sites. Taken together our results indicate that plant–microbe associations are context dependent, and that changes in enviro–climatic conditions will likely lead to network rewiring. Integrating turnover in plant–microbe interactions into studies that assess the impact of enviro–climatic change on peatland ecosystems is essential to understand ecosystem dynamics and must be combined with studies on the impact of these changes on ecosystem processes.     

Microbial ecology of chlorinated solvent biodegradation

This study focused on the microbial ecology of tetrachloroethene (PCE) degradation to trichloroethene, cis‐1,2‐dichloroethene and vinyl chloride to evaluate the relationship between the microbial community and the potential accumulation or degradation of these toxic metabolites. Multiple soil microcosms supplied with different organic substrates were artificially contaminated with PCE. A thymidine analogue, bromodeoxyuridine (BrdU), was added to the microcosms and incorporated into the DNA of actively replicating cells. We compared the total and active bacterial communities during the 50‐day incubations by using phylogenic microarrays and 454 pyrosequencing to identify microorganisms and functional genes associated with PCE degradation to ethene. By use of this integrative approach, both the key community members and the ecological functions concomitant with complete PCE degradation could be determined, including the presence and activity of microbial community members responsible for producing hydrogen and acetate, which are critical for Dehalococcoides‐mediated PCE degradation. In addition, by correlation of chemical data and phylogenic microarray data, we identified several bacteria that could potentially oxidize hydrogen. These results demonstrate that PCE degradation is dependent on some microbial community members for production of appropriate metabolites, while other members of the community compete for hydrogen in soil at low redox potentials.     

Plant Species Composition Effects on Belowground Properties and the Resistance and Resilience of the Soil Microflora to a Drying Disturbance

We hypothesised that plant species composition and richness would affect soil chemical and microbial community properties, and that these in turn would affect soil microbial resistance and resilience to an experimentally imposed drying disturbance. We performed a container experiment that manipulated the composition and species richness of common pasture plant species (Trifolium repens, Lolium perenne, and Plantago lanceolata) by growing them in monoculture, and in all the possible two and three-way combinations, along with an unplanted control soil. Experimental units were harvested at four different times over a 16-month period to determine the effect of plant community development and seasonal changes in temperature and moisture on belowground properties. Results showed that plant species composition influenced soil chemistry, soil microbial community properties and soil microbial resistance and resilience. Soil from planted treatments generally showed reduced soil microbial resistance to drying compared to unplanted control soils. Soils from under T. repens showed a higher resistance and resilience than the soils from under P. lanceolata, and a higher resistance than soils from under L. perenne. We suggest that differences across soils in either resource limitation or soil microbial community structure may be responsible for these results. Plant species richness rarely affected soil microbial community properties or soil microbial resistance and resilience, despite having some significant effects on plant community biomass and soil nitrogen contents in some harvests. The effect that treatments had for most variables differed between harvests, suggesting that results can be altered by the stage of plant community development or by extrinsic environmental factors that varied with harvest timing. These results in combination show that soil microbial resistance and resilience was affected by plant community composition, and the time of measurement, but was largely unrelated to plant species richness.     

Gut microbial diversity across a contact zone for California voles: Implications for lineage divergence of hosts and mitonuclear mismatch in the assembly of the mammalian gut microbiome

Gut microbial diversity is thought to reflect the co‐evolution of microbes and their hosts as well as current host‐specific attributes such as genetic background and environmental setting. To explore interactions among these parameters, we characterized variation in gut microbiome composition of California voles (Microtus californicus) across a contact zone between two recently diverged lineages of this species. Because this contact zone contains individuals with mismatched mitochondrial‐nuclear genomes (cybrids), it provides an important opportunity to explore how different components of the genotype contribute to gut microbial diversity. Analyses of bacterial 16S rRNA sequences and joint species distribution modelling revealed that host genotypes and genetic differentiation among host populations together explained more than 50% of microbial community variation across our sampling transect. The ranked importance (most to least) of factors contributing to gut microbial diversity in our study populations were: genome‐wide population differentiation, local environmental conditions, and host genotypes. However, differences in microbial communities among vole populations (β‐diversity) did not follow patterns of lineage divergence (i.e., phylosymbiosis). Instead, among‐population variation was best explained by the spatial distribution of hosts, as expected if the environment is a primary source of gut microbial diversity (i.e., dispersal limitation hypothesis). Across the contact zone, several bacterial taxa differed in relative abundance between the two parental lineages as well as among individuals with mismatched mitochondrial and nuclear genomes. Thus, genetic divergence among host lineages and mitonuclear genomic mismatches may also contribute to microbial diversity by altering interactions between host genomes and gut microbiota (i.e., hologenome speciation hypothesis).     

Spatial and halophyte-associated microbial communities in intertidal coastal region of India

Microbial communities in intertidal coastal soils respond to a variety of environmental factors related to resources availability, habitat characteristics, and vegetation. These intertidal soils of India are dominated with Salicornia brachiata, Aeluropus lagopoides, and Suaeda maritima halophytes, which play a significant role in carbon sequestration, nutrient cycling, and improving microenvironment. However, the relative contribution of edaphic factors, halophytes, rhizosphere, and bulk sediments on microbial community composition is poorly understood in the intertidal sediments. Here, we sampled rhizosphere and bulk sediments of three dominant halophytes (Salicornia, Aeluropus, and Suaeda) from five geographical locations of intertidal region of Gujarat, India. Sediment microbial community structure was characterized using phospholipid fatty acid (PLFA) profiling. Microbial biomass was significantly influenced by the pH, electrical conductivity, organic carbon, nitrogen, and sodium and potassium concentrations. Multivariate analysis of PLFA profiles had significantly separated the sediment microbial community composition of regional sampling sites, halophytes, rhizosphere, and bulk sediments. Sediments from Suaeda plants were characterized by higher abundance of PLFA biomarkers of Gram-negative, total bacteria, and actinomycetes than other halophytes. Significantly highest abundance of Gram-positive and fungal PLFAs was observed in sediments of Aeluropus and Salicornia, respectively than in those of Suaeda. The rhizospheric sediment had significantly higher abundance of Gram-negative and fungal PLFAs biomarkers compared to bulk sediment. The results of the present study contribute to our understanding of the relative importance of different edaphic and spatial factors and halophyte vegetation on sediment microbial community of intertidal sediments of coastal ecosystem.     

Geomicrobiological Changes in Two Ephemeral Desert Playa Lakes in the Western United States

The geochemistry and microbiology of two ephemeral playa lakes in the Western United States, Surprise Valley Alkali Lake (SVAL) and Eldorado Playa (EP), were examined over one wetting cycle, revealing dramatic temporal changes in suspended mineralogy, aqueous chemistry, and bacterial populations. In SVAL the predominant suspended mineral changed from smectite to vermiculite and clinoptilolite, which led to a depletion of soluble Mg²⁺. Nitrate became depleted in both playas as a result of biological nitrogen demand imparted by unusually dense microbial communities reaching ～1 × 10⁸ cultivable heterotrophs per ml of water. One hundred eighty eight bacterial isolates were obtained, representing sixty phylotypes and four phyla: Actinobacteria, Bacteroidetes, Proteobacteria, and Firmicutes. Phylogenetic analyses suggested that the microbial communities reflected different phases of succession, with SVAL changing from a diverse community with abundant Yonghaparkia to a less diverse late summer community with abundant Bacteroidetes and Proteobacteria such as Loktanella, Rhodobaca, Saccharospirillum, Flexibacter, and phylogenetically novel members of the Flexibacteriaceae. In EP, a diverse assemblage of bacteria often associated with soils was replaced very quickly by a much less even community dominated by Yonghaparkia, Sandarakinorhabdus, and relatives of Belliella baltica. Strikingly, the early summer microbial community from SVAL was not significantly different from the EP community that developed within one week of flooding, even though these playas are almost 1000 km apart, whereas sympatric communities in different phases of succession were different. To our knowledge, this is one of the first geomicrobiological studies of a recharge playa, the dominant playa type worldwide.     

Dissimilatory sulphate reduction in hypersaline coastal pans: an integrated microbiological and geochemical study

Here, we report on the spatial and temporal variation in sulphate‐reducing bacterial community structure and activity in three hypersaline coastal pans. Community structure was determined using denaturing gradient gel electrophoresis (DGGE). Cluster analysis of DGGE patterns indicated that similar microbial populations were generally found in individual pans but varied from one pan to the other. Sulphate reducing bacteria (SRB) were quantified by competitive polymerase chain reaction based on the amplification of the dsrAB genes. Cell numbers and in situ sulphate reduction activities varied between seasons and pans but in general showed low variation in depth. Sulphate reduction activity was not correlated with microbial population size indicating that community composition is relevant for specific microbial processes. Principal component analysis coupled with correlation analyses suggested that salinity, sulphate concentration, C/N ratio and pH were the most important factors in explaining variations in SRB community composition. Most sequences derived from DGGE amplicons belonged to members of the Desulfobacteraceae and Desulfohalobiaceae families.     

长期氮添加对亚热带森林土壤微生物碳源代谢多样性的影响

土壤微生物功能多样性对维持生态系统功能和稳定性具有非常重要的意义。人类活动造成全球氮沉降量激增,会引起土壤微生物群落结构和功能的改变,但是目前有关亚热带森林生态系统土壤微生物碳源利用多样性对模拟N沉降的响应还不是很清楚。依托位于鼎湖山的长达15年的长期野外模拟氮沉降试验样地平台,借助Biolog-Eco微平板技术,分析探讨了不同N添加量对季风常绿阔叶林中土壤微生物群落碳代谢功能多样性的影响差异及机制。研究结果表明:(1)与对照相比,长期低N、中N和高N量添加使土壤微生物碳源代谢活性(AWCD)分别显著降低了15.3%、32.9%和38.0%;并且显著降低了微生物碳源利用Shannon多样性指数和丰富度指数;(2)微生物对糖类、羧酸、氨基酸、胺类和酚酸类的利用随着施N水平的提高而显著降低;其中胺类最为敏感,长期高N添加下其利用强度与对照相比显著降低了80.2%;(3)主成分分析表明,不同N添加水平显著影响了土壤微生物碳源利用(P=0.001);(4)分类变异分析表明,土壤和植物因素可解释不同N水平下碳源利用差异的90.7%;(5)典型对应分析发现,土壤pH(P=0.009)是解释不同N水平添加处理间土壤微生物碳源代谢多样性差异的主要环境因子;而植被丰富度和凋落物量没有显著影响。综上所述,长期不同N添加显著影响了亚热带森林土壤微生物碳源代谢多样性,并且结果表明土壤pH是影响碳源利用多样性的主要影响因素。研究结果对于揭示全球变化影响下热带森林生态系统地下生物多样性维持机制提供了重要理论依据。     

The importance of dispersal related and local factors in shaping the taxonomic structure of diatom metacommunities

To date, little is known about the relative importance of dispersal related versus local factors in shaping microbial metacommunities. A common criticism regarding existing datasets is that the level of taxonomic resolution might be too coarse to reliably assess microbial community structure and study biogeographical patterns. Moreover, few studies have assessed the importance of geographic distance between habitats, which may influence metacommunity dynamics through its effect on dispersal rates. We applied variation partitioning analyses to 15 separate regional datasets on diatoms found in lakes in Eurasia, Africa and Antarctica. These analyses quantified the relative contributions of dispersal related and local factors in determining patterns of taxonomic turnover at the species and at the genus level. In general, results were similar at both taxonomic levels. Local environmental factors accounted for most of the explained variation (median=21%), whereas dispersal related factors were much less important (median of significant fractions=5.5% variation explained) and failed to significantly explain any variation, independent of the environmental variables, in the majority of the datasets. However, the amount of variation explained by dispersal related factors increased with increasing geographic distance and increasing taxonomic resolution. We extrapolated our regional scale observations to the global scale by combining the regional datasets into a global dataset comprising 1039 freshwater lakes from both hemispheres and spanning a geographic distance of over 19 000  km. At this global scale, taxonomic turnover was lowest in highly connected habitats, once environmental factors were partialled out. In common with many other studies of macro-organisms, these analyses showed that both dispersal related and local variables significantly contribute to the structure of global lacustrine diatom communities.