scholarly journals Abiotic factors influence patterns of bacterial diversity and community composition in the Dry Valleys of Antarctica

2020 ◽  
Vol 96 (5) ◽  
Author(s):  
Eric M Bottos ◽  
Daniel C Laughlin ◽  
Craig W Herbold ◽  
Charles K Lee ◽  
Ian R McDonald ◽  
...  
Keyword(s):  
Community Composition ◽  
Bacterial Communities ◽  
Structural Equation ◽  
Abiotic Factors ◽  
Biotic Interactions ◽  
Equation Modeling ◽  
Dry Valleys ◽  
Physicochemical Variables ◽  
Soil Conductivity ◽  
Community Dissimilarity

ABSTRACT The Dry Valleys of Antarctica are a unique ecosystem of simple trophic structure, where the abiotic factors that influence soil bacterial communities can be resolved in the absence of extensive biotic interactions. This study evaluated the degree to which aspects of topographic, physicochemical and spatial variation explain patterns of bacterial richness and community composition in 471 soil samples collected across a 220 square kilometer landscape in Southern Victoria Land. Richness was most strongly influenced by physicochemical soil properties, particularly soil conductivity, though significant trends with several topographic and spatial variables were also observed. Structural equation modeling (SEM) supported a final model in which variation in community composition was best explained by physicochemical variables, particularly soil water content, and where the effects of topographic variation were largely mediated through their influence on physicochemical variables. Community dissimilarity increased with distance between samples, and though most of this variation was explained by topographic and physicochemical variation, a small but significant relationship remained after controlling for this environmental variation. As the largest survey of terrestrial bacterial communities of Antarctica completed to date, this work provides fundamental knowledge of the Dry Valleys ecosystem, and has implications globally for understanding environmental factors that influence bacterial distributions.

Nematode communities of Byers Peninsula, Livingston Island, maritime Antarctica

2011 ◽  
Vol 23 (4) ◽  
pp. 349-357 ◽  
Author(s):  
Uffe N. Nielsen ◽  
Diana H. Wall ◽  
Grace Li ◽  
Manuel Toro ◽  
Byron J. Adams ◽  
...  
Keyword(s):  
Community Composition ◽  
Abiotic Factors ◽  
Biotic Interactions ◽  
Terrestrial Ecosystems ◽  
Nematode Species ◽  
Trophic Group ◽  
Maritime Antarctica ◽  
Nematode Communities ◽  
Livingston Island ◽  
Harsh Conditions

AbstractThe nematode communities of Antarctica are considered simple. The few species present are well adapted to the harsh conditions and often endemic to Antarctica. Knowledge of Antarctic terrestrial ecosystems is increasing rapidly, but nematode communities remain to be explored in large parts of Antarctica. In soil samples collected at Byers Peninsula (Antarctic Specially Protected Area No. 126), Livingston Island we recorded 37 nematode taxa but samples showed great variation in richness and abundance. Nematode richness decreased with increasing soil pH, whereas total abundances, and the abundance of several trophic groups, were greatest at intermediate pH (around 6.5–7). Moreover, the community composition was mainly related to pH and less so to soil moisture. Trophic group, and total nematode, rotifer and tardigrade, abundances were generally positively correlated. Byers Peninsula is thus, by maritime Antarctic standards, a nematode biodiversity hotspot, and the presence of several previously unrecorded genera indicates that nematode species richness in maritime Antarctica is probably underestimated. Our results indicate that abiotic factors influence nematode communities with little evidence for biotic interactions. The unexplained heterogeneity in community composition is probably related to variation in microclimate, vegetation, topography and unmeasured soil properties, but may also be contributed to by biological processes.

scholarly journals Dispersal limitation and thermodynamic constraints govern spatial structure of permafrost microbial communities

2018 ◽  
Author(s):  
Eric M. Bottos ◽  
David W. Kennedy ◽  
Elvira B. Romero ◽  
Sarah J. Fansler ◽  
Joseph M. Brown ◽  
...  
Keyword(s):  
Microbial Community ◽  
Variable Selection ◽  
Microbial Communities ◽  
Community Composition ◽  
Structural Equation ◽  
Microbial Community Composition ◽  
Dispersal Limitation ◽  
Equation Modeling ◽  
Permafrost Soil ◽  
Total Selection

AbstractUnderstanding drivers of permafrost microbial community composition is critical for understanding permafrost microbiology and predicting ecosystem responses to thaw, however studies describing ecological controls on these communities are lacking. We hypothesize that permafrost communities are uniquely shaped by constraints imposed by prolonged freezing, and decoupled from factors that influence non-permafrost soil communities. To test this hypothesis, we characterized patterns of environmental variation and microbial community composition in permafrost across an Alaskan boreal forest landscape. We used null modeling to estimate the relative importance of selective and neutral assembly processes on community composition, and identified environmental factors influencing ecological selection through regression and structural equation modeling (SEM). Proportionally, the strongest process influencing community composition was dispersal limitation (0.36), exceeding the influence of homogenous selection (0.21), variable selection (0.16), and homogenizing dispersal (0.05). Fe(II) content was the most important factor explaining variable selection, and was significantly associated with total selection by univariate regression (R2=0.14, p=0.003). SEM supported a model in which Fe(II) content mediated influences of the Gibbs free energy of the organic matter pool and organic acid concentration on total selection. These findings reveal that the processes shaping microbial communities in permafrost are distinct from those in non-permafrost soils, as the stability of the permafrost environment imposes dispersal and thermodynamic constraints on permafrost communities. Models of permafrost community composition will need to account for these unique drivers in order to predict community characteristics across permafrost landscapes, and in efforts to understand how pre-thaw conditions will influence post-thaw ecological and biogeochemical processes.

scholarly journals Phylogeography needs extrinsic causal theory

2020 ◽  
Author(s):  
Greer Dolby
Keyword(s):  
Structural Equation Modeling ◽  
Structural Equation ◽  
Biotic Interactions ◽  
Directed Acyclic Graphs ◽  
Interdisciplinary Studies ◽  
Equation Modeling ◽  
Natural Systems ◽  
Geological Processes ◽  
The Earth ◽  
Causal Structures

The overarching goal of phylogeography and the Earth-life sciences is to understand how geological and climatic processes contribute to the generation and distribution of the diversity of life on Earth. This question, at its heart, is one of causation. Causal structures are used to explain the cause-effect relations within natural systems and can be quantitatively evaluated through structural equation modeling. Here, I suggest that causality provides an organizing framework for linking extrinsic (geological) processes with genetic diversification and species richness that can be broadly applied. By using causal structures within individualistic taxonomic and geographic studies, we can tackle higher-order questions to reveal how Earth shapes life through time. Causal diagrams and structural equation modeling allow the abstraction of variables to accommodate (1) the heterogeneity of individual study systems, and (2) the need to reduce the complexity in interdisciplinary studies. Using directed acyclic graphs to articulate these relationships yield actionable hypotheses that feed directly back into Earth-life theory. I suggest many classically studied features, such as mountain ranges, are aggregate features whose causal effects can be decomposed into networks of indirect causal paths that are empirically testable. Formalizing causal relationships mitigates against the risk of mis-assigning causality, which can cloud our understanding of how the Earth-life system functions. Finally, this approach formalizes a way to test ideas about the top-down causation of biodiversity. Knowing how much of life is extrinsically forced would in turn reveal the importance of biotic-biotic interactions as well as intrinsic organismal and stochastic effects in shaping the diversity we see today.

scholarly journals Abiotic Drivers of Seedling Bank Diversity in Subtropical Forests of Southern China

2021 ◽  
Vol 9 ◽  
Author(s):  
Francesco Martini ◽  
Chaobo Zou ◽  
Xiaoyang Song ◽  
Uromi Manage Goodale
Keyword(s):  
Species Richness ◽  
Soil Properties ◽  
Community Composition ◽  
Soil Nutrients ◽  
Diversity Index ◽  
Abiotic Factors ◽  
Equation Modeling ◽  
Subtropical Forests ◽  
Adult Trees ◽  
Seedling Community

Abiotic factors are important to shape plant community composition and diversity through processes described as environmental filtering. Most studies on plant diversity in forests focus on adult trees, while the abiotic drivers of forest seedling community characteristics are less understood. Here, we studied seedling banks’ composition, richness, diversity, and abundance, and investigated their relationships with microsite abiotic conditions along a wide elevational gradient. We sampled seedling communities in 312 1-m2 quadrats, distributed in 13 one-ha plots in four subtropical forests in south China, covering an elevation gradient of 1500 m, for 2 years. We measured light availability, slope, and 11 soil nutrients for each seedling quadrat. We used analysis of similarities and multivariate analysis of variance to compare the composition and abiotic drivers of the four forests’ seedling communities. We then used mixed models and structural equation modeling to test the direct and indirect effects of abiotic factors on seedling species richness, diversity, and abundance. The differences in seedling community composition among these forests were mostly explained by differences in elevations and soil nutrients. Seedling diversity as Shannon and Simpson diversity index decreased with increasing elevation and increased with increasing slope, but seedling abundance and species richness did not. Elevation had an indirect effect on Simpson’s diversity index through modulating the direct effects of soil properties. Our findings show that soil properties play a prominent role in favoring differentiation in species composition among the four forests we studied and provide additional evidence to decreasing species diversity with elevation. However, this was reflected in decreasing Shannon and Simpson indices rather than species richness, which is more commonly studied. Whether and to what extent future environmental changes in climate and soil acidification will alter future forest composition and diversity needs to be investigated.

Evaluating the Scale Dependence of Biodiversity-productivity Relationships: A Case Study in Mountain Meadow Habitat

2021 ◽  
Author(s):  
Jiajia Liu ◽  
Xue-Jun Ge
Keyword(s):  
Structural Equation ◽  
Abiotic Factors ◽  
Regional Scale ◽  
Chemical Properties ◽  
Elevational Gradient ◽  
Equation Model ◽  
Equation Modeling ◽  
Scale Dependency ◽  
Ecological Communities ◽  
Natural Habitats

Abstract Ecological scale has been widely assumed to influence various biodiversity-productivity relationships in ecological communities; however, its robustness has not been extensively studied. In this study, we tested the scale dependency of biodiversity-productivity relationships by evaluating their direct linkages while considering other confounders, and simultaneously incorporating functional traits and interspecific phylogenetic relationships. We surveyed sixty quadrats each with an area of 0.25 m2 in three different meadows located along an elevational gradient in Yulong Mountain, China. We calculated different biodiversity parameters (richness, evenness, functionality, and phylogeny), and evaluated the chemical properties of soil from all quadrats, correlating their relationships with plant productivity at the local and regional scale. The direct and indirect relationships of biodiversity and productivity were evaluated using structural equation modeling. The biodiversity-productivity relationships were weak and inconsistent at the local scale, whereas some biodiversity metrics (richness, functional, and phylogenetic) showed either strong positive or negative relationships with productivity at the regional scale. However, a direct correlation between productivity and variables such as soil pH and community-weighted mean leaf carbon content was observed in the structural equation model reconstructed. Our study indicates that the scale dependency of biodiversity-productivity relationships in natural habitats may not be as strong as it may have been previously perceived, in case of taxonomic, functional, and phylogenetic diversity, respectively. Our study emphasizes the necessity to account for the confounding effects of abiotic factors when evaluating biodiversity-productivity relationship in natural habitats at regional or even worldwide scales.

scholarly journals Habitat filtering differentially modulates phylogenetic vs functional diversity relationships between dominant ground-dwelling arthropods in salt marshes

2020 ◽  
Author(s):  
Aurélien Ridel ◽  
Denis Lafage ◽  
Pierre Devogel ◽  
Thomas Lacoue-Labarthe ◽  
Julien Pétillon
Keyword(s):  
Salt Marshes ◽  
Structural Equation ◽  
Evolutionary History ◽  
Abiotic Factors ◽  
Taxonomic Diversity ◽  
Coi Gene ◽  
Equation Modeling ◽  
Pitfall Trapping ◽  
Spatial And Temporal Scales ◽  
Colonization Process

AbstractWhile mechanisms underlying biological diversities at different scales received huge attention over the last decades, whether local abiotic factors driving functional and phylogenetic diversities can differ among ecologically and phylogenetically closely related taxa remains under-investigated. In this study, we compared correlations and drivers of functional (FD) and phylogenetic (PD) diversities between two dominant taxa of ground-dwelling arthropods in salt marshes, spiders and carabids. Pitfall trapping in two sampling sites of N-W France resulted in the collection and identification of more than 7000 individuals belonging to 67 species. Morphological and behavioral traits, as well as molecular sequences of COI gene, were attributed to all species for calculating functional and phylogenetic diversities respectively. Both taxa exhibited high correlation between FD and PD, which was even higher in carabids probably due to their lower species richness. Analyses using Bayesian framework and structural equation modeling revealed that FD and PD were positively influenced by taxonomic diversity in spiders and carabids, but abiotic factors driving FD and PD differed between taxa. Salinity especially drove the taxonomic diversity of carabids, but not that of spiders, suggesting that spiders are more plastic and less selected by this factor. Phylogenetic diversity was conversely influenced by salinity in spiders but not in carabids. This interesting result can be interpreted by different evolutionary history and colonization process of salt marshes between the two model taxa. Our study finally highlights that, even in taxa of the same phylum and occupying the same niche in a highly constrained habitat, functional and phylogenetic diversities can have different drivers, showing different filtering mechanisms and evolutionary history at small spatial and temporal scales.

scholarly journals Crossing Treeline: Bacterioplankton Communities of Alpine and Subalpine Rocky Mountain Lakes

2022 ◽  
Vol 12 ◽  
Author(s):  
Kim Vincent ◽  
Hannah Holland-Moritz ◽  
Adam J. Solon ◽  
Eli M. S. Gendron ◽  
Steven K. Schmidt
Keyword(s):  
Environmental Factors ◽  
Community Composition ◽  
Bacterial Communities ◽  
Rocky Mountain ◽  
Early Summer ◽  
Mountain Lakes ◽  
Mountain Watersheds ◽  
Subalpine Lakes ◽  
Key Players ◽  
Community Dissimilarity

From the aboveground vegetation to the belowground microbes, terrestrial communities differ between the highly divergent alpine (above treeline) and subalpine (below treeline) ecosystems. Yet, much less is known about the partitioning of microbial communities between alpine and subalpine lakes. Our goal was to determine whether the composition of bacterioplankton communities of high-elevation mountain lakes differed across treeline, identify key players in driving the community composition, and identify potential environmental factors that may be driving differences. To do so, we compared bacterial community composition (using 16S rDNA sequencing) of alpine and subalpine lakes in the Southern Rocky Mountain ecoregion at two time points: once in the early summer and once in the late summer. In the early summer (July), shortly after peak runoff, bacterial communities of alpine lakes were distinct from subalpine lakes. Interestingly, by the end of the summer (approximately 5 weeks after the first visit in August), bacterial communities of alpine and subalpine lakes were no longer distinct. Several bacterial amplicon sequence variants (ASVs) were also identified as key players by significantly contributing to the community dissimilarity. The community divergence across treeline found in the early summer was correlated with several environmental factors, including dissolved organic carbon (DOC), pH, chlorophyll-a (chl-a), and total dissolved nitrogen (TDN). In this paper, we offer several potential scenarios driven by both biotic and abiotic factors that could lead to the observed patterns. While the mechanisms for these patterns are yet to be determined, the community dissimilarity in the early summer correlates with the timing of increased hydrologic connections with the terrestrial environment. Springtime snowmelt brings the flushing of mountain watersheds that connects terrestrial and aquatic ecosystems. This connectivity declines precipitously throughout the summer after snowmelt is complete. Regional climate change is predicted to bring alterations to precipitation and snowpack, which can modify the flushing of solutes, nutrients, and terrestrial microbes into lakes. Future preservation of the unique alpine lake ecosystem is dependent on a better understanding of ecosystem partitioning across treeline and careful consideration of terrestrial-aquatic connections in mountain watersheds.

scholarly journals Bacterial Diversity and Community Composition Distribution in Cold-Desert Habitats of Qinghai–Tibet Plateau, China

2021 ◽  
Vol 9 (2) ◽  
pp. 262
Author(s):  
Wei Zhang ◽  
Ali Bahadur ◽  
Wasim Sajjad ◽  
Gaosen Zhang ◽  
Fahad Nasir ◽  
...  
Keyword(s):  
Bacterial Community ◽  
Bacterial Diversity ◽  
Community Composition ◽  
Bacterial Communities ◽  
Desert Ecosystem ◽  
Tibet Plateau ◽  
Vegetation Coverage ◽  
Cold Desert ◽  
Physicochemical Variables ◽  
Qinghai Tibet Plateau

Bacterial communities in cold-desert habitats play an important ecological role. However, the variation in bacterial diversity and community composition of the cold-desert ecosystem in Qinghai–Tibet Plateau remains unknown. To fill this scientific gape, Illumina MiSeq sequencing was performed on 15 soil samples collected from different cold-desert habitats, including human-disturbed, vegetation coverage, desert land, and sand dune. The abundance-based coverage estimator, Shannon, and Chao indices showed that the bacterial diversity and abundance of the cold-desert were high. A significant variation reported in the bacterial diversity and community composition across the study area. Proteobacteria accounted for the largest proportion (12.4–55.7%) of all sequences, followed by Actinobacteria (9.2–39.7%), Bacteroidetes (1.8–21.5%), and Chloroflexi (2.7–12.6%). Furthermore, unclassified genera dominated in human-disturbed habitats. The community profiles of GeErMu, HongLiangHe, and CuoNaHu sites were different and metagenomic biomarkers were higher (22) in CuoNaHu sites. Among the soil physicochemical variables, the total nitrogen and electric conductivity significantly influenced the bacterial community structure. In conclusion, this study provides information regarding variation in diversity and composition of bacterial communities and elucidates the association between bacterial community structures and soil physicochemical variables in cold-desert habitats of Qinghai–Tibet Plateau.

scholarly journals Biotic Interactions in Experimental Antarctic Soil Microcosms Vary with Abiotic Stress

Soil Systems ◽  
2019 ◽  
Vol 3 (3) ◽  
pp. 57
Author(s):  
E. Ashley Shaw ◽  
Diana H. Wall
Keyword(s):  
High Salinity ◽  
Abiotic Factors ◽  
Biotic Interactions ◽  
Trophic Relationships ◽  
Salinity Treatment ◽  
Ecological Communities ◽  
Dry Valleys ◽  
Top Down ◽  
Terrestrial Vertebrates ◽  
The Many

Biotic interactions structure ecological communities but abiotic factors affect the strength of these relationships. These interactions are difficult to study in soils due to their vast biodiversity and the many environmental factors that affect soil species. The McMurdo Dry Valleys (MDV), Antarctica, are relatively simple soil ecosystems compared to temperate soils, making them an excellent study system for the trophic relationships of soil. Soil microbes and relatively few species of nematodes, rotifers, tardigrades, springtails, and mites are patchily distributed across the cold, dry landscape, which lacks vascular plants and terrestrial vertebrates. However, glacier and permafrost melt are expected to cause shifts in soil moisture and solutes across this ecosystem. To test how increased moisture and salinity affect soil invertebrates and their biotic interactions, we established a laboratory microcosm experiment (4 community × 2 moisture × 2 salinity treatments). Community treatments were: (1) Bacteria only (control), (2) Scottnema (S. lindsayae + bacteria), (3) Eudorylaimus (E. antarcticus + bacteria), and (4) Mixed (S. lindsayae + E. antarcticus + bacteria). Salinity and moisture treatments were control and high. High moisture reduced S. lindsayae adults, while high salinity reduced the total S. lindsayae population. We found that S. lindsayae exerted top-down control over soil bacteria populations, but this effect was dependent on salinity treatment. In the high salinity treatment, bacteria were released from top-down pressure as S. lindsayae declined. Ours was the first study to empirically demonstrate, although in lab microcosm conditions, top-down control in the MDV soil food web.

scholarly journals Trophic interactions as determinants of the arbuscular mycorrhizal fungal community with cascading plant-promoting consequences

Microbiome ◽  
2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Yuji Jiang ◽  
Lu Luan ◽  
Kaijie Hu ◽  
Manqiang Liu ◽  
Ziyun Chen ◽  
...  
Keyword(s):  
Community Composition ◽  
Trophic Interactions ◽  
Fungal Community ◽  
Mycorrhizal Fungi ◽  
Structural Equation ◽  
Plant Pathogens ◽  
Arbuscular Mycorrhizal ◽  
Plant Performance ◽  
Equation Modeling ◽  
Amf Communities

Abstract Background The soil mycobiome is composed of a complex and diverse fungal community, which includes functionally diverse species ranging from plant pathogens to mutualists. Among the latter are arbuscular mycorrhizal fungi (AMF) that provide phosphorous (P) to plants. While plant hosts and abiotic parameters are known to structure AMF communities, it remains largely unknown how higher trophic level organisms, including protists and nematodes, affect AMF abundance and community composition. Results Here, we explored the connections between AMF, fungivorous protists and nematodes that could partly reflect trophic interactions, and linked those to rhizosphere P dynamics and plant performance in a long-term manure application setting. Our results revealed that manure addition increased AMF biomass and the density of fungivorous nematodes, and tailored the community structures of AMF, fungivorous protists, and nematodes. We detected a higher abundance of AMF digested by the dominant fungivorous nematodes Aphelenchoides and Aphelenchus in high manure treatments compared to no manure and low manure treatments. Structural equation modeling combined with network analysis suggested that predation by fungivorous protists and nematodes stimulated AMF biomass and modified the AMF community composition. The mycorrhizal-fungivore interactions catalyzed AMF colonization and expression levels of the P transporter gene ZMPht1;6 in maize roots, which resulted in enhanced plant productivity. Conclusions Our study highlights the importance of predation as a key element in shaping the composition and enhancing the biomass of AMF, leading to increased plant performance. As such, we clarify novel biological mechanism of the complex interactions between AMF, fungivorous protists, and nematodes in driving P absorption and plant performance.

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