Drivers Of Community Structure Research Articles

Interspecies interactions in dairy biofilms drive community structure and response against cleaning and disinfection

Interspecies interactions within a biofilm community influence population dynamics and community structure, which in turn may affect the bacterial stress response to antimicrobials. This study was conducted to assess the impact of interactions between Kocuria salsicia and a three-species biofilm community (comprising Stenotrophomonas rhizophila, Bacillus licheniformis, and Microbacterium lacticum) on biofilm mass, the abundance of individual species, and their survival under a laboratory-scale cleaning and disinfection (C&D) regime. The presence of K. salsicia enhanced the cell numbers of all three species in pairwise interactions. The outcomes derived from summing up pairwise interactions did not accurately predict the bacterial population dynamics within communities of more than two species. In four-species biofilms, we observed the dominance of S. rhizophila and B. licheniformis, alongside a concurrent reduction in the cell counts of K. salsicia and M. lacticum. This pattern suggests that the underlying interactions are not purely non-transitive; instead, a more complex interplay results in the dominance of specific species. We observed that bacterial spatial organization and matrix production in different mixed-species combinations affected survival in response to C&D. Confocal microscopy analysis of spatial organization showed that S. rhizophila localized on the biofilm formed by B. licheniformis and M. lacticum, and S. rhizophila was more susceptible to C&D. Matrix production in B. licheniformis, evidenced by alterations in biofilm mass and by scanning electron microscopy, demonstrated its protective role against C&D, not only for this species itself, but also for neighbouring species. Our findings emphasise that various social interactions within a biofilm community not only affect bacterial population dynamics but also influence the biofilm community's response to C&D stress.

Size‐dependent community patterns differ between microbial eukaryotes and bacteria in a permafrost lake–river–sea continuum

AbstractMicrobial communities play a crucial role in ecosystem functioning, with contributions that can vary among taxonomic domains and size fractions. However, microbial assembly processes for bacteria and eukaryotes are seldom characterized together using size fractionation, especially in flowing waters. Here, we used amplicon sequencing combined with physicochemical measurements to determine how size fractionated (small fraction 0.22–3 μm; large fraction > 3 μm) community structure and diversity varied over a subarctic river continuum. We sampled the Sheldrake River, a 25 km river flowing through degrading discontinuous permafrost, from its lacustrine source through subarctic forest shrub tundra to its discharge plume in eastern Hudson Bay (Nunavik, Canada). Microbial community structure differed by size fraction and among habitats, with differences in the variables potentially driving community structure among size fractions and microbial domains. For the small size fraction, colored dissolved organic matter was a significant covariate of community variation for both bacteria and eukaryotes, consistent with the influence of landscape gradients. There were contrasting diversity patterns along the lake–river transect between bacterial size fractions. An abundance‐based approach indicated that for all communities, assembly processes were dominated by homogeneous selection, while an incidence‐based method showed dominance of heterogeneous selection for bacteria and homogenizing dispersal for microbial eukaryotes. Our findings show how different components of riverine microbial communities can have divergent patterns along the downstream continuum to the sea.

Temporal and environmental factors drive community structure and function of methanotrophs in volcanic forest soils

Temporal and environmental factors drive community structure and function of methanotrophs in volcanic forest soils

Year effects drive beta diversity, but unevenly across plant community types.

Year of establishment can be a critical driver of plant communities with the establishment stage of community development particularly susceptible to factors including ambient rain, temperature, and other temporally variable drivers (e.g., seed and seedling predators). However, while year effects have been shown to drive community structure at local (patch) scales, it is yet unexplored how these within-patch effects scale up to drive landscape-level patterns of biodiversity. These dynamics are likely to be critical but are overlooked in many systems including those with high-frequency disturbance regimes or active management. Here we leveraged a series of field-based grassland mesocosms established identically at three sites across 5 years, and each monitored for 4-8 years. We compared the strength of these temporal and spatial drivers (year effects and site effects) on consequent patterns of spatial and temporal variability (beta diversity and turnover) between plots seeded with native perennial species versus those seeded with nonnative annual species. The composition of plots seeded with perennial species showed strong effects of planting year and consequently exhibited higher beta diversity within sites (across mesocosms established in five different years within sites), while plots seeded with annual species had higher between-site variation but low beta diversity within sites. Plots with annual species were also more temporally variable than plots with perennial species. These findings have important implications for our understanding of key drivers of biodiversity across landscapes. Specifically, we showed that variable trajectories in community composition generated by site and year effects during establishment can promote beta diversity across landscapes dominated by perennial species, but are considerably less impactful in annual-dominated systems. These findings further our understanding of the importance of assembly dynamics on landscape-scale patterns of diversity, and have important management implications for restoration efforts.

The distribution of subarctic and boreal deep-sea demersal fish assemblages across environmental gradients of the northwest Atlantic.

The oceanography of the Labrador Sea is well studied because of its globally important deep-water convection that oxygenates the deep ocean and drives climate-regulating ocean currents. However, little is known about the fish communities that inhabit this area, particularly beyond the depths accessible to standard research surveys and commercial fishing activities. We used baited longline surveys to characterize important components of demersal fish communities across a depth gradient of 200-3000 m and compared these data to a similar dataset collected c. 1200 km to the south in the Flemish Cap Region. We found demersal fish communities in the Labrador Sea to be similar to those of the Flemish Cap Region despite unique oceanography and lower primary productivity in the Labrador Sea. Moreover, both areas had high abundance, biomass, and species richness at intermediate depths that suggests factors beyond depth drive community structure in the deep ocean. These data are important for identifying high-value areas for potential protective measures in the northwest Atlantic and provide necessary data with which to assess potential environmental impacts of extractive industries that are expanding north and to deeper waters.

Landscape-scale floral resource discontinuity decreases bumble bee occurrence and alters community composition.

Agricultural practices and intensification during the past two centuries have dramatically altered the abundance and temporal continuity of floral resources that support pollinating insects such as bumble bees. Long-term trends among bumble bees within agricultural regions suggest that intensive agricultural conditions have created inhospitable conditions for some species, while other species have maintained their relative abundances despite landscape-level changes in flower availability. Bumble bee responses to spatiotemporal resource heterogeneity have been explored at the colony and behavioral level, but we have yet to understand whether these conditions drive community structure and ultimately explain the diverging patterns in long-term species trends. To explore the relationship between landscape-level floral resource continuity and the likelihood of bumble bee occurrence, we mapped the relative spatial and temporal availability of floral resources within an intensive agricultural region in the US Upper Midwest and related this resource availability with bumble bee species relative abundance. Across the bee community, we found that relative bumble bee occurrence increases in landscapes containing more abundant and more temporally continuous floral resources. Declining species, such as Bombus terricola, exhibited the strongest, positive responses to resource abundance and continuity whereas common, stable species, such as Bombus impatiens, showed no statistical relationship to either. Together with existing experimental evidence, this work suggests that efforts to increase spatiotemporal flower availability, along with overall flower abundance at landscape scales may have positive effects on bumble bee communities in the US Upper Midwest.

Movement of protistan trophic groups in soil-plant continuums.

Protists, functionally divided into consumers, phototrophs, and parasites act as integral components and vital regulators of microbiomes in soil-plant continuums. However, the drivers of community structure, assembly mechanisms, co-occurrence patterns, and the associations with human pathogens and different protistan trophic groups remain unknown. Here, we characterized the phyllosphere and soil protistan communities associated with three vegetables under different fertilization treatments (none and organic fertilization) at five growth stages. In this study, consumers were the most diverse soil protist group, had the role of inter-kingdom connector, and were the primary biomarker for rhizosphere soils which were subjected to decreasing deterministic processes during plant growth. In contrast, phototrophs had the greatest niche breadth and formed soil protistan hubs, and were the primary biomarkers for both bulk soils and the phyllosphere. Parasites had minimal input to microbial co-occurrence networks. Organic fertilization increased the relative abundance (RA) of pathogenic protists and the number of pathogen-consumer connections in rhizosphere soils but decreased protistan richness and the number of internal protistan links. This study advances our understanding of the ecological roles and potential links between human pathogens and protistan trophic groups associated with soil-plant continuums, which is fundamental to the regulation of soil-plant microbiomes and maintenance of environmental and human health.

Upper Ocean Biogeochemistry of the Oligotrophic North Pacific Subtropical Gyre: From Nutrient Sources to Carbon Export

AbstractSubtropical gyres cover 26%–29% of the world's surface ocean and are conventionally regarded as ocean deserts due to their permanent stratification, depleted surface nutrients, and low biological productivity. Despite tremendous advances over the past three decades, particularly through the Hawaii Ocean Time‐series and the Bermuda Atlantic Time‐series Study, which have revolutionized our understanding of the biogeochemistry in oligotrophic marine ecosystems, the gyres remain understudied. We review current understanding of upper ocean biogeochemistry in the North Pacific Subtropical Gyre, considering other subtropical gyres for comparison. We focus our synthesis on spatial variability, which shows larger than expected dynamic ranges of properties such as nutrient concentrations, rates of N2 fixation, and biological production. This review provides new insights into how nutrient sources drive community structure and export in upper subtropical gyres. We examine the euphotic zone (EZ) in subtropical gyres as a two‐layered vertically structured system: a nutrient‐depleted layer above the top of the nutricline in the well‐lit upper ocean and a nutrient‐replete layer below in the dimly lit waters. These layers vary in nutrient supply and stoichiometries and physical forcing, promoting differences in community structure and food webs, with direct impacts on the magnitude and composition of export production. We evaluate long‐term variations in key biogeochemical parameters in both of these EZ layers. Finally, we identify major knowledge gaps and research challenges in these vast and unique systems that offer opportunities for future studies.

Metagenome-based metabolic modelling predicts unique microbial interactions in deep-sea hydrothermal plume microbiomes

Deep-sea hydrothermal vents are abundant on the ocean floor and play important roles in ocean biogeochemistry. In vent ecosystems such as hydrothermal plumes, microorganisms rely on reduced chemicals and gases in hydrothermal fluids to fuel primary production and form diverse and complex microbial communities. However, microbial interactions that drive these complex microbiomes remain poorly understood. Here, we use microbiomes from the Guaymas Basin hydrothermal system in the Pacific Ocean to shed more light on the key species in these communities and their interactions. We built metabolic models from metagenomically assembled genomes (MAGs) and infer possible metabolic exchanges and horizontal gene transfer (HGT) events within the community. We highlight possible archaea–archaea and archaea–bacteria interactions and their contributions to the robustness of the community. Cellobiose, D-Mannose 1-phosphate, O2, CO2, and H2S were among the most exchanged metabolites. These interactions enhanced the metabolic capabilities of the community by exchange of metabolites that cannot be produced by any other community member. Archaea from the DPANN group stood out as key microbes, benefiting significantly as acceptors in the community. Overall, our study provides key insights into the microbial interactions that drive community structure and organisation in complex hydrothermal plume microbiomes.

Influence of upwelling on coral reef benthic communities: a systematic review and meta-analysis.

Highly competitive coral reef benthic communities are acutely sensitive to changes in environmental parameters such as temperature and nutrient concentrations. Physical oceanographic processes that induce upwelling therefore act as drivers of community structure on tropical reefs. How upwelling impacts coral communities, however, is not fully understood; upwelling may provide a natural buffer against climate impacts and could potentially enhance the efficacy of spatial management and reef conservation efforts. This study employed a systematic review to assess existing literature linking upwelling with reef community structure, and a meta-analysis to quantify upwelling impact on the percentage cover of coral reef benthic groups. We show that upwelling has context-dependant effects on the cover of hard coral and fleshy macroalgae, with effect size and direction varying with depth, region and remoteness. Fleshy macroalgae were found to increase by 110% on inhabited reefs yet decrease by 56% around one well-studied remote island in response to upwelling. Hard coral cover was not significantly impacted by upwelling on inhabited reefs but increased by 150% when direct local human pressures were absent. By synthesizing existing evidence, this review facilitates adaptive and nuanced reef management which considers the influence of upwelling on reef assemblages.

Species differences in stoichiometric homeostasis affect grassland community stability under N and P addition

Unbalanced N and P input has substantially altered the relative importance of N and P limitation in grassland ecosystems, which resulted in profound impacts on species nutrient cycling, community structure, and ecosystem stability. However, the underlying species-specific nutrient use strategy and stoichiometric homeostasis in driving community structure and stability changes remain unclear. A split-plot N and P addition experiment (main-plot: 0, 25, 50, and 100 kgN hm-2 a-1; subplot: 0, 20, 40, and 80 kgP2O5 hm-2 a-1) was conducted during 2017-2019 in two typical grasslands (perennial grass and perennial forb) communities in the Loess Plateau. The stoichiometric homeostasis of 10 main component species, species dominance, stability changes, and their contribution to community stability were investigated. Perennial legume and perennial clonal species tend to perform higher stoichiometric homeostasis than non-clonal and annual forb. Large shifts in species with high homeostasis vs. low homeostasis caused by N and P addition showed consistently profound impacts on community homeostasis and stability in both communities. In both two communities, species dominance performed significantly positive relationships with homeostasis under no N and P addition. P alone or combined with 25 kgN hm-2 a-1 addition strengthened species dominance-homeostasis relationship and increased community homeostasis due to increased perennial legumes. Under 50 and 100 kgN hm-2 a-1 combined with P addition, species dominance-homeostasis relationships were weakened, and community homeostasis decreased significantly in both communities, which was due to that increased annual and non-clonal forb suppressed perennial legume and clonal species. Our results demonstrated that trait-based classifications of species-level homeostasis offer a reliable tool in predicting species performance and community stability under N and P addition, and conserving species with high homeostasis is important to enhance semiarid grassland ecosystem function stability on the Loess Plateau.

Phytoplankton and macroinvertebrate diversity and eco-exergy responses to rainfall diverge in semiarid reservoirs

Rainfall is a variable that drives community structure in aquatic ecosystems and is even more important in dry regions. Most studies have evaluated how the seasonal variation of rainfall influences aquatic communities. However, studies that evaluate the influence of spatial gradients of rainfall on aquatic organisms are scarce, especially regarding biological diversity and thermodynamic information. This study evaluated the response from diversity metrics and thermodynamic indices (eco-exergy and specific eco-exergy) in phytoplankton and benthic macroinvertebrate communities in 13 reservoirs distributed along a spatial gradient of rainfall in the Brazilian semiarid region. We hypothesized that the phytoplankton and benthic macroinvertebrate communities are congruent in response to the spatial gradient of rainfall in terms of diversity and thermodynamic indices in semiarid reservoirs. We expect to find higher values of biomass and the eco-exergy index under lower rainfall. To test our hypothesis, generalized linear models (GLMs) were used to relate the effects of rainfall changes on community structure. The eco-exergy and specific eco-exergy indices of the phytoplankton community were positively related to rainfall and reflected a greater investment in biomass production and genetic information (e.g., Chlorophyceae). As for the macroinvertebrate community, the reduction in rainfall promoted a greater investment in energy storage by generalist organisms (e.g., Melanoides tuberculata and some genera of Chironomidae). Thus, for a holistic evaluation of ecosystem health, the joint analysis of thermodynamic indices associated with an assessment of taxonomic composition, diversity and taxonomic richness is important, providing a more complete and multifaceted response. Additionally, thermodynamic indices better reflected the changes in both aquatic communities in response to rainfall, and were more sensitive than the diversity and richness indices. Consequently, the thermodynamic indices represent an efficient tool in the assessment of aquatic community responses to climate change, even when these communities respond in an opposite manner.

Habitat area and local habitat conditions outweigh fragmentation effects on insect communities in vineyards

Abstract Fragmentation of habitat, for example by intensive agricultural practices, can be detrimental to local biodiversity. However, it often remains unclear whether such biodiversity declines are caused by loss of habitat area or increased fragmentation, and how habitat quality factors into it. In our study system, vegetated vineyards are typically small, and isolated from one another, potentially limiting the distribution and dispersal of organisms. In a full‐factorial experiment of a priori selected vegetated vineyard patches of differing size and fragmentation, we aimed to disentangle the effects of habitat area (area of vegetated vineyards), habitat fragmentation (number of vegetated vineyards per 100 ha) and field‐scale ground vegetation density on ground beetle, leafhopper and wild bee communities using a combined framework of multiscale and multispecies modelling (Hierarchical Model of Species Communities). We demonstrate variable effects of habitat area, fragmentation and local ground vegetation density on the three insect groups: Increased habitat area at fine scales favours higher species richness of leafhoppers, while local vegetation density boosts species richness of both leafhoppers and ground beetles, whereas no community‐level responses were detected for wild bees. We conclude that increased ground vegetation density at both field and landscape scales (i.e. higher habitat area) favours more diverse and abundant insect communities, while fragmentation effects are highly variable and species specific. In addition, our results highlight that mainly ground beetles and leafhoppers will benefit from simple ground greening measures in vineyards, while for wild bees environmental factors other than the ones tested here may drive community structure. We recommend increasing the number and area of vegetated vineyards (even at small spatial scales) requiring more nature‐friendly farming practices especially regarding a reduction or renunciation from herbicide applications, while the within‐field vegetation density should optimally be intermediate or high to favour a diverse insect community.

The role of environmental variables in shaping temperate coralline algae communities across large spatial scales

ABSTRACTCoralline algae are ecologically important macroalgae providing settlement cues and habitat for a number of marine organisms. They are abundant in a wide range of habitats in tropical to polar systems and are at severe risk from a number of local and global anthropogenic stressors. Despite their ecological importance, there are large gaps in understanding coralline algae diversity patterns and abiotic drivers of this diversity. Furthermore, recent advances in molecular identifications have revealed larger diversity than previously estimated through morphological approaches. The aim of this study was to explore coralline algal community composition in a modern context using DNA-based species identifications and to examine broad-scale environmental variables driving community structure around the New Zealand coastline. Hierarchical cluster techniques identified seven distinct coralline algal communities in the region. Sea surface temperature (SST) and light at seabed explained significant variation in coralline algal community composition, with SST explaining the highest amount of variation. Both SST and light are important for the growth, calcification and survival of coralline algae, and responses to these environmental parameters can vary widely among species. Wave exposure indices and turbidity were not found to have a large influence in shaping coralline community structure, most likely due to the ability of coralline algae to tolerate mechanical stress and periods of intense sand scouring and burial. Understanding the drivers structuring diversity, particularly for ecologically important primary producers, provides insights into community and ecosystem functioning and contributes to our baseline understanding of current species distribution.

Microhabitat thermal environment controls community structure of macrobenthos on coastal infrastructures

The proliferation of coastal infrastructure in the context of coastal development, urbanization, and global change is inevitably related to the transformation of coastal community structure. For restoration of biodiversity in these human-disturbed coastal ecosystems, it is vital to untangle the community structure and thermal environments, with the consideration of the microhabitat-scale thermal environment variations. In the present study, we measured the species richness, α-diversity (i.e. the species composition of each surface of breakwaters), and β-diversity (i.e. the dissimilarities among macrobenthic communities of different surfaces of breakwater) of macrobenthos on the breakwaters on a tropical shore for understanding the variation of the community structure of macrobenthos; we also monitored the operative temperatures in different surfaces of the breakwaters during the experimental period for investigating the roles of microhabitat thermal environment on the community structure of macrobenthos on the artificial infrastructure. Our results showed that there were higher species richness and abundance in the thermally benign microhabitats. The variations of β-diversity indicated that the community structure underwent dramatic changes in different microhabitats and seasons. The population dynamics of thermal-sensitive species (e.g. Patelloida pygmaea, Cellana toreuma, and Siphonaria japonica) largely contributed to the changes in community structure. Redundancy analysis (RDA) results showed that maximum temperature, temperature predictability (i.e. the degree to which a temperature data point in a time series is influenced by its historical values), and heating rate were important thermal characteristics driving community structure on the artificial infrastructure. These results indicate the heterogeneity of thermal environments among different microhabitats is crucial for maintaining the community structure of macrobenthos on the artificial infrastructure and suggest that structural complexity should be considered for biodiversity conservation in the design and construction of coastal infrastructure.

South West Atlantic salt marshes as model systems for community and ecosystem ecology

Just as some species are used as model systems in organismal biology (e.g., physiology, genetics), many ecosystems are commonly used as model systems in ecology. Salt marshes, for instance, are great models to perform manipulative field experiments, and thus, were historically used to understand the drivers of community and ecosystem function. Decades of experimental work, indeed, made a strong contribution to community ecology as a discipline, but most of the emerged hypotheses and models were grounded in a few sites. When studies from new sites came onboard, looking to enlarge generalities, their results challenged the prevailing ideas. Here, we review more than 25 years of intense experimentation in South West Atlantic salt marshes, which helped not only to increase the knowledge about salt marsh functioning, but also to expand this knowledge beyond salt marshes helping to refine community and ecosystem function theory. We show that results coming from SW Atlantic marshes significantly contribute to understand 1) the separate and interactive effect of biotic and abiotic stress for species distribution and even for ecosystem stability, 2) the integrated role of species that can function as ecosystem engineers and as consumers, 3) the balance between stochastic and deterministic forces as drivers of community structure and 4) the regulation of cross-ecosystem fluxes. Nevertheless, we believe SW Atlantic salt marshes still have a lot more to offer, not only as conceptual models that help satisfy our intellectual curiosity, but also as key ecosystems that provide valuable benefits to our societies.

Driving factors of phytoplankton trace metal concentrations and distribution along anthropogenically-impacted estuaries of southern Taiwan

Phytoplankton are key marine components in global primary productivity and ocean biogeochemistry. However, anthropogenic activities impact phytoplankton through toxic metal dispersion—threatening the food web with increased metal bioaccumulation. This study assessed the phytoplankton trace metal concentrations, distribution, and relationship with community structure. Environmental parameters (temperature, salinity, pH, dissolved oxygen, biological oxygen demand, suspended solids, chlorophyll-a, ammonium, nitrate, nitrite, phosphate, silicate, total phosphorus) and phytoplankton were collected in southern Taiwan; from five transects (estuaries; T1–T5), composed of estuarine (Es) and offshore (Os) sites. This study respectively used size and density fractionation to accurately measure phytoplankton trace metals. Results showed that anthropogenically-impacted rivers and marine outfall discharges drive community structure and phytoplankton trace metal distribution. Among sites, T3–T5Es differed in its environmental characteristics. Significant differences on environmental characteristics and trace metals in phytoplankton were found between transects—indicating higher anthropogenic impacts in T3 (Dianbao–Houjin estuary) and T4 (Kaohsiung Harbor estuary). Phytoplankton trace metals follows an order of Fe >> Mn > Cr > Cu > Ni > Co > As > Pb > Hg. Metals in estuarine phytoplankton were higher compared offshore, but not significantly different (p > 0.05), highlighting the role of marine outfalls in offshore pollutant diffusion. Phytoplankton metal distribution showed a distinct spatial gradient between agriculture- and industry-associated areas. Significantly high Cr bioaccumulation factor (BCF > 100) were also found in transects T2 and T4. Overall, this study presents an accurate trace metal data and BCF in phytoplankton of southern Taiwan. Further, insights on the potential relationship between phytoplankton community structure and trace metal concentrations are presented – with nutrients mainly impacting phytoplankton community, initiating a ripple effect which likely favored blooming of metal-tolerant species (high dominance) – increasing the trace metal bioaccumulation.

Response of arid‐land macroinvertebrate communities to extremes of drought, wildfire, and monsoonal flooding

AbstractObserving spatial and temporal variation in aquatic communities provides insight into factors driving community structure. These observations are particularly important as ecosystems are being challenged by new extremes associated with a changing climate. However, since the timing of disturbances is unpredictable, capturing their effects is difficult, unless a study is already gathering data prior to and after these events. During a 2008–2016 study on the spatial and temporal variation of aquatic macroinvertebrate communities in the Gila River of New Mexico, a severe drought from 2011 to 2013, two mega‐wildfires in 2011 and 2012, and the third‐largest monsoon flood on record in 2013 occurred, providing an opportunity to document how these disturbances structure macroinvertebrate communities. Taxonomic richness and biomass of many individual taxa decreased following the wildfires and the extreme flood, yet the total biomass of the macroinvertebrate community decreased only slightly. We also found an association between the response of some taxa to inter‐annual variation in hydrologic conditions and habitat use. This was evidenced by an increase in the relative biomass of taxa associated with pool habitats, such as Nematoda and Ceratopogonidae during drought years, whereas taxa from riffle habitats, such as mayfly (Leptophlebiidae) and stonefly (Perlodidae) nymphs increased in biomass in relatively wet years. Two groups of stonefly nymphs (Nemouridae and Taeniopterygidae) notably increased following the large monsoonal flooding in 2013. Collectively, the observed responses of macroinvertebrates to extreme hydrologic, wildfire and climate disturbances suggest that increasing frequency of disturbance might result in directional changes in the macroinvertebrate communities due to taxa‐specific responses to those events.

Contrasting Community Assembly Forces Drive Microbial Structural and Potential Functional Responses to Precipitation in an Incipient Soil System.

Microbial communities in incipient soil systems serve as the only biotic force shaping landscape evolution. However, the underlying ecological forces shaping microbial community structure and function are inadequately understood. We used amplicon sequencing to determine microbial taxonomic assembly and metagenome sequencing to evaluate microbial functional assembly in incipient basaltic soil subjected to precipitation. Community composition was stratified with soil depth in the pre-precipitation samples, with surficial communities maintaining their distinct structure and diversity after precipitation, while the deeper soil samples appeared to become more uniform. The structural community assembly remained deterministic in pre- and post-precipitation periods, with homogenous selection being dominant. Metagenome analysis revealed that carbon and nitrogen functional potential was assembled stochastically. Sub-populations putatively involved in the nitrogen cycle and carbon fixation experienced counteracting assembly pressures at the deepest depths, suggesting the communities may functionally assemble to respond to short-term environmental fluctuations and impact the landscape-scale response to perturbations. We propose that contrasting assembly forces impact microbial structure and potential function in an incipient landscape; in situ landscape characteristics (here homogenous parent material) drive community structure assembly, while short-term environmental fluctuations (here precipitation) shape environmental variations that are random in the soil depth profile and drive stochastic sub-population functional dynamics.

Temperature Loggers Capture Intraregional Variation of Inundation Timing for Intermittent Ponds

AbstractHydroperiod, or the amount of time a lentic waterbody contains water, shapes communities of aquatic organisms. Precise measurement of hydroperiod features such as inundation timing and duration can help predict community dynamics and ecosystem stability. In areas defined by high spatial and temporal variability, fine‐scale temporal variation in inundation timing and duration may drive community structure, but that variation may not be captured using common approaches including remote sensing technology. Here, we provide methods to accurately capture inundation timing by fitting hidden Markov models to measurements of daily temperature SD collected from temperature loggers. We describe a rugged housing design to protect loggers from physical damage and apply our methods to a group of intermittent ponds in southeastern Arizona, showing that initial pond inundation timing is highly variable across a small geographic scale (∼50 km2). We also compare a 1‐logger (pond only) and 2‐logger (pond + control) design and show that, although a single logger may be sufficient to capture inundation timing in most cases, a 2‐logger design can increase confidence in results. These methods are cost‐effective and show promise in capturing variation in intraregional inundation timing for a range of temporary lentic habitats that may have profound effects on aquatic communities, with implications for how these communities may respond to hydroperiod alteration from a changing climate.