Turnover In Community Composition Research Articles

Microcystin influence on soil-plant microbiota: Unraveling microbiota modulations and assembly processes in the rhizosphere of Vicia faba

Microcystins (MCs) are frequently detected in cyanobacterial bloom-impacted waterbodies and introduced into agroecosystems via irrigation water. They are widely known as phytotoxic cyanotoxins, which impair the growth and physiological functions of crop plants. However, their impact on the plant-associated microbiota is scarcely tackled and poorly understood. Therefore, we aimed to investigate the effect of MCs on microbiota-inhabiting bulk soil (BS), root adhering soil (RAS), and root tissue (RT) of Vicia faba when exposed to 100 μg L−1 MCs in a greenhouse pot experiment. Under MC exposure, the structure, co-occurrence network, and assembly processes of the bacterial microbiota were modulated with the greatest impact on RT-inhabiting bacteria, followed by BS and, to a lesser extent, RAS. The analyses revealed a significant decrease in the abundances of several Actinobacteriota-related taxa within the RT microbiota, including the most abundant and known genus of Streptomyces. Furthermore, MCs significantly increased the abundance of methylotrophic bacteria (Methylobacillus, Methylotenera) and other Proteobacteria-affiliated genera (e.g., Paucibacter), which are supposed to degrade MCs. The co-occurrence network of the bacterial community in the presence of MCs was less complex than the control network. In MC-exposed RT, the turnover in community composition was more strongly driven by deterministic processes, as proven by the beta-nearest taxon index. Whereas in MC-treated BS and RAS, both deterministic and stochastic processes can influence community assembly to some extent, with a relative dominance of deterministic processes. Altogether, these results suggest that MCs may reshape the structure of the microbiota in the soil-plant system by reducing bacterial taxa with potential phytobeneficial traits and increasing other taxa with the potential capacity to degrade MCs.

Relic DNA confounds the results of DNA-based study on microeukaryotic succession in aquatic biofilms

High-throughput sequencing has revolutionized the DNA sequence-based study of microbial community and diversity on an unprecedented scale. Relic DNA is widespread in the natural aquatic environment; however, the extent to which such DNA can bias the sequence-based analysis of living microeukaryotic communities is unclear. Here, we conducted a 30-day field-control experiment investigating biofilm succession of microeukaryotic communities on glass slides and polyurethane foam units (PFUs) in a subtropical urban reservoir, using DNA-based approach. The propidium monoazide (PMA) dye was used to distinguish living and relic DNA sequences. Our results showed that microeukaryotic community succession in biofilms was time and substratum dependent, which was correlated with changing environmental conditions, nutrients and microalgae. Most importantly, relic DNA has a significant influence on the estimation of beta diversity and turnover in community composition, importantly its presence masked the successional patterns of different microbial taxa. We found strong deterministic processes dominating microeukaryotic succession on glass slides and PFUs biofilms. Depending on substrate and the presence and absence of relic DNA sequences, contrasting community assembly mechanisms were observed. In the presence of relic DNA, our results showed that 0.53–3.15 % of dispersal limitation, and 13.16 % of homogeneous selection processes were overestimated, while 1.06–3.68 % of homogenizing dispersal, 2.11–10.53 % of undominated and 2.10–10.52 % of heterogeneous selection processes were underestimated. This study provides significant insights into the value of removing relic DNA when designing DNA-based studies to characterize microeukaryotic communities and raise questions about some ecological interpretations in molecular microbial ecology which have not accounted for the effects of relic DNA.

Effects of compositional heterogeneity and spatial autocorrelation on richness and diversity in simulated landscapes

AbstractLandscape structure plays a key role in mediating a variety of ecological processes affecting biodiversity patterns; however, its precise effects and the mechanisms underpinning them remain unclear. While the effects of landscape structure have been extensively investigated both empirically and theoretically from a metapopulation perspective, the effects of spatial structure at the landscape scale remain poorly explored from a metacommunity perspective. Here, we attempt to address this gap using a spatially explicit, individual‐based metacommunity model to explore the effects of landscape compositional heterogeneity and per se spatial configuration on diversity at the landscape and patch levels via their influence on long‐term community assembly processes. Our model simulates communities composed of species of annual, asexual organisms living, reproducing, dispersing, and competing within grid‐based, fractal landscapes that vary in their magnitude of spatial environmental heterogeneity and in their degree of spatial environmental autocorrelation. Communities are additionally subject to temporal environmental fluctuations and external immigration, allowing for turnover in community composition. We found that compositional heterogeneity and spatial autocorrelation had differing effects on richness, diversity, and the landscape and patch scales. Landscape‐level diversity was driven by community dissimilarity at the patch level and increased with greater heterogeneity, while landscape richness was largely the result of the short‐term accumulation of immigrants and decreased with greater compositional heterogeneity. Both richness and diversity decreased in variance with greater compositional heterogeneity, indicating a reduction in community turnover over time. Patch‐level richness and diversity patterns appeared to be driven by overall landscape richness and local mass effects, resulting in maximum patch‐level richness and diversity at moderate levels of compositional heterogeneity and high spatial autocorrelation.

Geology and elevation shape bacterial assembly in Antarctic endolithic communities

Ice free areas of continental Antarctica are among the coldest and driest environments on Earth, and yet, they support surprisingly diverse and highly adapted microbial communities. Endolithic growth is one of the key adaptations to such extreme environments and often represents the dominant life-form. Despite growing scientific interest, little is known of the mechanisms that influence the assembly of endolithic microbiomes across these harsh environments. Here, we used metagenomics to examine the diversity and assembly of endolithic bacterial communities across Antarctica within different rock types and over a large elevation range. While granite supported richer and more heterogeneous communities than sandstone, elevation had no apparent effect on taxonomic richness, regardless of rock type. Conversely, elevation was clearly associated with turnover in community composition, with the deterministic process of variable selection driving microbial assembly along the elevation gradient. The turnover associated with elevation was modulated by geology, whereby for a given elevation difference, turnover was consistently larger between communities inhabiting different rock types. Overall, selection imposed by elevation and geology appeared stronger than turnover related to other spatially-structured environmental drivers.Our findings indicate that at the cold-arid limit of life on Earth, geology and elevation are key determinants of endolithic bacterial heterogeneity. This also suggests that warming temperatures may threaten the persistence of such extreme-adapted organisms.

Ecosystem consequences of invertebrate decline

Human activities cause substantial changes in biodiversity.1,2 Despite ongoing concern about the implications of invertebrate decline,3,4,5,6,7 few empirical studies have examined the ecosystem consequences of invertebrate biomass loss. Here, we test the responses of six ecosystem services informed by 30 above- and belowground ecosystem variables to three levels of aboveground (i.e., vegetation associated) invertebrate community biomass (100%, 36%, and 0% of ambient biomass) in experimental grassland mesocosms in a controlled Ecotron facility. In line with recent reports on invertebrate biomass loss over the last decade, our 36% biomass treatment also represented a decrease in invertebrate abundance (-70%) and richness (-44%). Moreover, we simulated the pronounced change in invertebrate biomass and turnover in community composition across the season. We found that the loss of invertebrate biomass decreases ecosystem multifunctionality, including two critical ecosystem services, aboveground pest control and belowground decomposition, while harvested plant biomass increases, likely because less energy was channeled up the food chain. Moreover, communities and ecosystem functions become decoupled with a lower biomass of invertebrates. Our study shows that invertebrate loss threatens the integrity of grasslands by decoupling ecosystem processes and decreasing ecosystem-service supply.

Soil Micro-eukaryotic Diversity Patterns Along Elevation Gradient Are Best Estimated by Increasing the Number of Elevation Steps Rather than Within Elevation Band Replication.

The development of high-throughput sequencing (HTS) of environmental DNA (eDNA) has stimulated the study of soil microbial diversity patterns and drivers at all scales. However, given the heterogeneity of soils, a challenge is to define effective and efficient sampling protocols that allow sound comparison with other records, especially vegetation. In studies of elevational diversity pattern, a trade-off is choosing between replication within elevation bands vs. sampling more elevation bands. We addressed this question for soil protists along an elevation gradient on Mt. Asahi, Hokkaido, Japan. We compared two sampling approaches: (1) the replicate strategy (five replicates at six elevational bands, total = 30) and (2) the transect strategy (one sample in each of 16 different elevational bands). Despite a nearly twofold lower sampling effort, the transect strategy yielded congruent results compared to the replicate strategy for the estimation of elevational alpha diversity pattern: the regression coefficients between diversity indices and elevation did not differ between the two options. Furthermore, for a given total number of samples, gamma diversity estimated across the entire transect was higher when sampling more elevational bands as compared to replication from fewer elevational bands. Beta diversity (community composition turnover) was lower within a given elevational band than between adjacent bands and increased with elevation distance. In redundancy analyses, soil organic matter-related variable (the first principal component of soil organic matter, water content, total organic carbon, and nitrogen by whom were highly correlated) and elevation best explained elevational beta diversity pattern for both sampling approaches. Taken together, our results suggest that sampling a single plot per elevation band will be sufficient to obtain a good estimate of soil micro-eukaryotic diversity patterns along elevation gradients. This study demonstrated the effectiveness of the transect strategy in estimating diversity patterns along elevation gradients which is instructive for future environmental or even experimental studies. While not advocating for completely replacing replication-based sampling practices, it is important to note that both replicate and transect strategies have their merits and can be employed based on specific research goals and resource limitations.

Control of diatom and chrysophyte cyst dynamics by a meteorologically driven mixing regime in eutrophic Lake Żabińskie, northern Poland

Abstract Ongoing climate warming has strong moderating control over aquatic processes, such as ice cover duration, length of the growing season, vertical mixing patterns, thermal stratification, and the availability of light and nutrients. These fundamental mechanisms in turn influence the population dynamics of aquatic organisms such as diatoms and chrysophytes. In our study, over 3.5 years with contrasting meteorological conditions, we investigated eutrophic Lake Żabińskie located in northeast Poland. By combining observational data of meteorological conditions, physicochemical variables measured in the water column, and modern sedimentation, we sought to explain the relationships between changes in meteorological conditions, dynamics of total fluxes and the taxonomic composition of diatoms and chrysophyte cysts. Our results show the direct influence of meteorological conditions on physicochemical conditions and their indirect influence on total diatom and chrysophyte cyst fluxes and taxonomic succession. The former refers to the importance of air temperature and wind speed in shaping the mixing regime of Lake Żabińskie, while the latter refers to the nutrient cycling driven by changes in the mixing regime, which in turn influences the formation of biotic signals in the sediment. Our study also revealed that the biotic response to unusual meteorological conditions that occurred in 2020 (i.e., warm winter without ice cover) differed from typical years in terms of the phenology of diatom and chrysophyte cyst blooms. However, this response was not as pronounced as in lakes with lower productivity and can be attributed to the already turbid conditions and high nutrient concentrations, which alter the threshold for noticeable changes to occur. The taxonomic composition of diatoms and chrysophyte cysts also changed in response to changes in meteorological conditions. Complex interactions between physical and chemical conditions masked the direct influences of meteorological conditions on lake biota under eutrophic conditions. Nevertheless, high‐resolution monitoring enabled indirect links to be recognised. Both phenology and turnover in community composition responded to changes in meteorological conditions. These results show how ongoing climate change might affect biota in eutrophic lakes in the future.

Ground-dwelling arthropods as biodiversity indicators in maize agroecosystems of Northern Italy

Reliable monitoring of arthropod diversity in a given agroecosystem is essential for the conservation of the related ecosystem services, such as biological control. The often daunting complexity of arthropod collection and identification, however, highlights the need for surrogate taxa that can be easily sampled and be representative of a number of other taxa in term of diversity, general community features and specific composition.In this study, we used pitfall traps to sample three ground-dwelling arthropod taxa important as biocontrol agents (ground beetles, rove beetles and spiders) in 9 conventionally managed maize agroecosystems of Northern Italy over the course of two years, with the goal of characterizing their assemblages and evaluating their reciprocal potential as indicators of activity density, species richness, community turnover and species co-occurrence.Although dominated by few generalist species, sampled arthropod communities were relatively species-rich, and included the first Italian record of the spider Zelotes metellus (Roewer) (Araneae: Gnaphosidae). Ground beetles as a group were confirmed as promising indicators for the species richness and community composition turnover of rove beetles and spiders. Additionally, several abundant arthropod species acted as indicators of the species richness of their respective groups, and the ground beetle Pterostichus macer (Marsham) also worked as an indicator of overall rove beetle activity density. While the co-occurrence of individual arthropod species was limited for the studied taxa, a few species such as the ground beetle Parophonus maculicornis (Duftschmid) did show promise as species-specific bioindicators. Our results could be useful in improving the monitoring and management of these important natural enemies in maize-growing regions.

High sensitivity of tropical forest birds to deforestation at lower altitudes.

Habitat conversion is a major driver of tropical biodiversity loss, but its effects are poorly understood in montane environments. While community-level responses to habitat loss display strong elevational dependencies, it is unclear whether these arise via elevational turnover in community composition and interspecific differences in sensitivity or elevational variation in environmental conditions and proximity to thermal thresholds. Here we assess the relative importance of inter- and intraspecific variation across the elevational gradient by quantifying how 243 forest-dependent bird species vary in sensitivity to landscape-scale forest loss across a 3000-m elevational gradient in the Colombian Andes. We find that species that live at lower elevations are strongly affected by loss of forest in the nearby landscape, while those at higher elevations appear relatively unperturbed, an effect that is independent of phylogeny. Conversely, we find limited evidence of intraspecific elevational gradients in sensitivity, with populations displaying similar sensitivities to forest loss, regardless of where they exist in a species' elevational range. Gradients in biodiversity response to habitat loss thus appear to arise via interspecific gradients in sensitivity rather than proximity to climatically limiting conditions.

From pastures to forests: Changes in Mediterranean wild bee communities after rural land abandonment

Abstract In farmland landscapes worldwide, there are pervasive trends for either intensification or abandonment. Intensification is a widely recognised driver of wild bee declines, but little is known about the consequences of land abandonment, though it involves major habitat shifts from fallows, pastures and meadows, to shrublands and forests. Focusing on a Mediterranean landscape, we investigated long‐term changes in wild bee communities during secondary vegetation succession after land abandonment. We used a space‐for‐time substitution approach, sampling plants and wild bees on five successional stages, from grasslands, through shrublands, to oak woodlands. We recorded 2721 bees, representing over 150 species. Grasslands had the highest wild bee abundance and high diversity of oligolectic species. Moving through successional stages, there was a rapid decline in bee abundance combined with a progressive accumulation of rare species, resulting in maximum diversity of the overall community, ground nesters, polyleges, and oligoleges in oak woodlands. Bee diversity was positively related to plant taxonomic and phylogenetic diversity. There was high turnover in community composition along the succession, with species occurring in grasslands being largely absent from later successional stages, and vice versa. From 21 indicator species, 17 were associated with grasslands, including the only threatened species. Our results suggest that a mosaic of habitats at different successional stages, particularly grasslands and oak woodlands, are necessary to maximise the diversity and abundance of wild bees at the landscape scale. Sustained management is thus needed under land abandonment to retain early‐successional herbaceous habitats and to ensure woodland regeneration and protection.

Null‐model analysis and changes in species interactions in biocrusts along a successional gradient in the Tengger Desert, northern China

AbstractAimsIn arid regions, the succession of biological soil crusts (biocrusts) usually accompanies substantial turnover of community composition. How interspecific interactions among biocrust‐forming mosses, lichens, algae and cyanobacteria change along the successional gradient is largely unknown. According to the stress gradient hypothesis (SGH), the frequency or intensity of facilitative and competitive interactions within the community will vary along an environmental stress gradient, with an increasing role of competition relative to facilitation under more benign environmental conditions. In the process of biocrust succession, decreasing soil stress also occurs because of slow soil amelioration, which meets the assumption of the SGH. Therefore, we hypothesize that the changes in facilitative and competitive interactions within biocrust communities will follow the prediction of the SGH and that the nature of biocrust interactions will also change.LocationSand‐binding vegetation belts for the Baotou–Lanzhou railway at the southeast fringe of the Tengger Desert in the Shapotou region of the Ningxia Hui Autonomous Region, western China.MethodsWe conducted a field evaluation at five adjacent sand‐binding vegetation belts built in chronosequence to study the successional gradient. Small‐scale patterns of co‐occurrence and null models were used to evaluate the community‐level interspecific interactions among the biocrust‐forming mosses, lichens, algae and cyanobacteria. In addition, an accessory method of species‐pair co‐occurrence based on null models was also applied to potentially identify the nature of the interspecific interactions within the biocrusts and for the causal investigation of these patterns.ResultsA strong spatial segregation of co‐occurrence patterns occurred between cyanobacteria and algae and species of mosses and lichens at early succession, and occurred among species of mosses and lichens at late succession, while the weak spatial aggregation between lichen species only occurred at middle succession.ConclusionsNegative interspecific interactions were prevalent within biocrusts throughout succession. The co‐occurrence patterns at both the community and species‐pair levels are consistent, supporting the unimodal version of the SGH that species interactions shift toward competition under extremely stressed conditions. Given the lack of research on interspecific interactions in biocrusts, our study is important for obtaining a deeper understanding of biocrust succession.

Seasonal turnover in community composition of stream‐associated macroinvertebrates inferred from freshwater environmental DNA metabarcoding

AbstractMacroinvertebrate communities are crucial for biodiversity monitoring and assessment of ecological status in stream ecosystems. However, traditional monitoring approaches require intensive sampling and rely on invasive morphological identifications that are time‐consuming and dependent on taxonomic expertise. Importantly, sampling is often only carried out once in a year, namely during late winter–spring, where most indicator taxa have larval stages in the streams. Hence, species with divergent phenology might not be detected. Here, we use environmental DNA (eDNA) metabarcoding of filtered water samples collected in both spring and autumn from five streams in Denmark to address seasonal turnover in community composition of stream macroinvertebrates. We find that eDNA read data from the same stream sampling site clearly show different communities in spring and autumn, respectively. For three of the five streams, season even appears to be a more important factor than sampling site for explaining the variation in community composition. Finally, we compare eDNA data with a near‐decadal dataset of taxon occurrences in the same five streams based on kick sampling conducted through a national monitoring program. This comparison reveals an overlap in species composition, but also that the two approaches provide complementary rather than identical insights into community composition. Our study demonstrates that aquatic eDNA metabarcoding is useful for species detection across highly diverse taxa and for identifying seasonal patterns in community composition of freshwater macroinvertebrates. Thus, our results have important implications for both fundamental research in aquatic ecology and for applied biomonitoring.

Contrasting drivers of diversity in hosts and parasites across the tropical Andes

Geographic turnover in community composition is created and maintained by eco-evolutionary forces that limit the ranges of species. One such force may be antagonistic interactions among hosts and parasites, but its general importance is unknown. Understanding the processes that underpin turnover requires distinguishing the contributions of key abiotic and biotic drivers over a range of spatial and temporal scales. Here, we address these challenges using flexible, nonlinear models to identify the factors that underlie richness (alpha diversity) and turnover (beta diversity) patterns of interacting host and parasite communities in a global biodiversity hot spot. We sampled 18 communities in the Peruvian Andes, encompassing ∼1,350 bird species and ∼400 hemosporidian parasite lineages, and spanning broad ranges of elevation, climate, primary productivity, and species richness. Turnover in both parasite and host communities was most strongly predicted by variation in precipitation, but secondary predictors differed between parasites and hosts, and between contemporary and phylogenetic timescales. Host communities shaped parasite diversity patterns, but there was little evidence for reciprocal effects. The results for parasite communities contradicted the prevailing view that biotic interactions filter communities at local scales while environmental filtering and dispersal barriers shape regional communities. Rather, subtle differences in precipitation had strong, fine-scale effects on parasite turnover while host-community effects only manifested at broad scales. We used these models to map bird and parasite turnover onto the ecological gradients of the Andean landscape, illustrating beta-diversity hot spots and their mechanistic underpinnings.

Scaling up biodiversity-ecosystem functioning relationships: the role of environmental heterogeneity in space and time.

The biodiversity and ecosystem functioning (BEF) relationship is expected to be scale-dependent. The autocorrelation of environmental heterogeneity is hypothesized to explain this scale dependence because it influences how quickly biodiversity accumulates over space or time. However, this link has yet to be demonstrated in a formal model. Here, we use a Lotka-Volterra competition model to simulate community dynamics when environmental conditions vary across either space or time. Species differ in their optimal environmental conditions, which results in turnover in community composition. We vary biodiversity by modelling communities with different sized regional species pools and ask how the amount of biomass per unit area depends on the number of species present, and the spatial or temporal scale at which it is measured. We find that more biodiversity is required to maintain functioning at larger temporal and spatial scales. The number of species required increases quickly when environmental autocorrelation is low, and slowly when autocorrelation is high. Both spatial and temporal environmental heterogeneity lead to scale dependence in BEF, but autocorrelation has larger impacts when environmental change is temporal. These findings show how the biodiversity required to maintain functioning is expected to increase over space and time.

Functionally reversible impacts of disturbances on lake food webs linked to spatial and seasonal dependencies.

Increasing human impact on the environment is causing drastic changes in disturbance regimes and how they prevail over time. Of increasing relevance is to further our understanding on biological responses to pulse disturbances (short duration) and how they interact with other ongoing press disturbances (constantly present). Because the temporal and spatial contexts of single experiments often limit our ability to generalize results across space and time, we conducted a modularized mesocosm experiment replicated in space (five lakes along a latitudinal gradient in Scandinavia) and time (two seasons, spring and summer) to generate general predictions on how the functioning and composition of multitrophic plankton communities (zoo-, phyto- and bacterioplankton) respond to pulse disturbances acting either in isolation or combined with press disturbances. As pulse disturbance, we used short-term changes in fish presence, and as press disturbance, we addressed the ongoing reduction in light availability caused by increased cloudiness and lake browning in many boreal and subarctic lakes. First, our results show that the top-down pulse disturbance had the strongest effects on both functioning and composition of the three trophic levels across sites and seasons, with signs for interactive impacts with the bottom-up press disturbance on phytoplankton communities. Second, community composition responses to disturbances were highly divergent between lakes and seasons: temporal accumulated community turnover of the same trophic level either increased (destabilization) or decreased (stabilization) in response to the disturbances compared to control conditions. Third, we found functional recovery from the pulse disturbances to be frequent at the end of most experiments. In a broader context, these results demonstrate that top-down, pulse disturbances, either alone or with additional constant stress upon primary producers caused by bottom-up disturbances, can induce profound but often functionally reversible changes across multiple trophic levels, which are strongly linked to spatial and temporal context dependencies. Furthermore, the identified dichotomy of disturbance effects on the turnover in community composition demonstrates the potential of disturbances to either stabilize or destabilize biodiversity patterns over time across a wide range of environmental conditions.

Temporal complementarity in activity‐density of two arthropod macro‐detritivore taxa

Abstract Macro‐detritivores are important fragmenters performing a first step in the ecosystem process of nutrient cycling. Woodlice and millipedes are important representatives of this group and their ecology and niche requirements are often regarded as very similar. However, it is unclear whether there is a difference in temporal activity throughout the year between both groups, possibly leading to temporal complementarity for leaf litter breakdown, and whether patterns of temporal variation in activity are consistent across different habitat types. We studied year‐round pitfall‐trap data of woodlice and millipedes from an old sand quarry with a high habitat heterogeneity. Our results indicate that there is high temporal complementarity between both detritivore taxa, with millipede activity‐density peaking in spring, while woodlice showing a peak in summer. Interestingly, timing of activity depended on habitat openness. Millipedes peak first in open habitat and later in closed habitat, while woodlice showed the opposite pattern. Temporal turnover in community composition was high and of similar magnitude as spatial turnover in community composition across this relatively small scale of our study area. We conclude that, although woodlice and millipedes show comparable habitat preferences, their temporal activity patterns show the potential for temporal complementarity for litter breakdown.

Bacterial community composition and assembly along a natural sodicity/salinity gradient in surface and subsurface soils

Soil microbes play a key role in terrestrial ecosystems. In the saline-sodic environment, the microbial communities and their community assembly processes, especially throughout soil profiles, however, are not well understood. Here, we characterized the soil microbial communities across three sodicity/salinity gradients to 1.0 m depth in the western Songnen Plain, Northeast China. Soil sodicity (exchangeable sodium percentage) and salinity (electrical conductivity) exerted a strong influence on bacterial community compositions compared with other soil properties. These filtering effects of sodicity/salinity were strong on the microbial communities in the layer of 0–60 cm across the three sites, with more contributions of deterministic processes over stochastic processes. As sodicity/salinity decreased, some potential biomarkers for a high community tolerance to salt or soda, such as KSA1, Halomonas, Euzebya and Bacillus, were depleted; meanwhile, some taxa associated with decomposition of organic matter and nutrient transformations, such as Arthrobacter, Mesorhizobium, Pseudomonas and Nitrospira, were enriched. Within each soil profile, the turnover in community composition was lower than between sites, and the stochastic processes (homogenizing dispersal) dominated the microbial assembly. Yet, the surface and deepest depth (80–100 cm) of saline-sodic soils still harbored some distinct microbial communities. The near-surface (20–40 cm) may serve as a gating role for limiting surface microbial penetrance into the deeper depth. Taken together, our results show that sodicity/salinity can strongly structure soil microbial communities, and emphasize the importance of soil depth as an environmental gradient on the assembly processes in saline-sodic soils.

Population turnover promotes fungal stability in a semi-arid grassland under precipitation shifts

Abstract Aims Bacteria and fungi are two primary groups of soil microbes, and their stability determines the persistence of microbial functions in response to a changing environment. Recent studies reported higher fungal than bacterial stability under precipitation alteration, the underlying mechanisms, however, remain elusive. Methods A 3-year precipitation manipulation experiment in a semi-arid grassland was used to compare the bacterial and fungal diversities, including alpha diversity, beta diversity and microbial community composition turnover, in response to precipitation manipulations. A framework is proposed to understand the stability properties of bacteria and fungi under precipitation alteration. We conceived a diagrammatic valley to illustrate microbial stability with the depth representing resistance and the width ecological resilience. Important Findings We found that ±60% in precipitation significantly reduced the richness and increased the evenness of bacteria but had trivial impacts on fungi. Precipitation alteration yielded stronger impacts on the variation in alpha diversity of bacteria than fungi, suggesting that the bacterial community is more sensitive to water stress than the fungal community. Moreover, fungi had wider composition turnover than that of bacteria, indicating higher composition variation of fungi than bacteria. The population turnover of fungi, reflected by composition variation, coefficient variation of diversity index and composition turnover, was larger than that of bacteria at both temporal and spatial scales, indicating the population turnover promotes fungal stability. The higher stability of fungal community in tolerating water stress is analogous to a ball in a wide valley that swing substantially but remain close to its steady state; while the lower stability of bacteria community is analogous to a ball that swings slightly but stay far away from its steady state. Our finding that the fungal community had higher stability than bacterial community in a semi-arid grassland might be applicable to other biomes.

Microbial community composition turnover and function in the mesophilic phase predetermine chicken manure composting efficiency

The aim of this work was to study the influence of inoculation with microbial inoculants (MI) or mature compost (MC) by comparing the resultant composting efficiency with that in a noninoculated (CK) treatment. MI and MC application both accelerated the composting process according to fluorescence excitation-emission matrix (EEM) detection and germination index testing. Bacterial and fungal community composition both differed significantly over the composting period. However, the turnover of the initial bacterial community played a significant role in the composting process, and the key operational taxonomic units (OTUs) of MI (OTU_26, Thermicanus) and MC (OTU_48, Tepidimicrobium) showed significant explanatory power for the formation of humic acid-like and fulvic acid-like substances, respectively, during the stage of composting. Thus, our results indicate that microbial inoculation accelerates the composting process by stimulating key resident microbes in the initial stage.

Exploring the homogeneity of terrestrial subterranean communities at a local spatial scale

1. Although caves are generally perceived as isolated habitats, at the local scale, they are often interconnected via a network of fissures in the bedrock. Accordingly, caves in close proximity are expected to host the same, or very similar, animal communities.2. We explored the extent to which subterranean arthropod communities are homogenous at a local spatial scale of less than 1 km2, along with which cave‐specific environmental features result in a departure from the expected homogeneous pattern. We approached this question by studying richness and turnover in terrestrial invertebrate communities of 27 caves in a small karst massif in the Western Italian Alps.3. Specialised subterranean species were homogeneously distributed among caves and were not influenced by seasonality. The only factor driving their distribution was the distance from the cave entrance, with deeper caves yielding a greater diversity of species.4. Significant spatio‐temporal turnover in species not specialised to subterranean life was observed. In summer, there was a significant homogenisation of the community and a more even distribution of species among sites; in winter, these species were missing or found exclusively at greater depths, where environmental conditions were more stable. Furthermore, caves at lower elevations yielded, on average, a greater diversity and abundance of these species.5. This study demonstrated that the theoretical expectation of no turnover in community composition in caves in close proximity is not always met. Turnover can be mostly attributed to seasonal patterns and sampling depth; thus, our findings have implications for planning sampling and monitoring activities in caves.