Important Ecosystem Functions Research Articles

The complete female mitogenome of Potomida semirugata (Lamarck, 1819)

Freshwater mussels perform important ecological functions in ecosystems, such as water filtration and energy cycling. Unlike marine bivalves, freshwater mussels have unique characteristics including internal fertilization and parental care. Some freshwater mussels are facing a high risk of extinction due to several factors such as climate change and habitat loss. Potomida semirugata (Lamarck, 1819) is one of the freshwater mussel species with a high risk of extinction and listed as Endangered in the Red List of the International Union for Conservation of Nature. Here, we present the first F-type mitogenome sequence of P. semirugata. The genome was sequenced on an Illumina high-throughput platform from a P. semirugata specimen collected from the Tersakan River (Turkey). The 16,093 bp mitochondrial genome sequence contains 13 protein-coding genes, 22 transfer RNAs, and two ribosomal RNAs. Phylogenetic analysis placed P. semirugata in the Lamprotulini clade with Potomida littoralis, as expected. Potomida semirugata is a poorly studied species and the genomic resource provided here will contribute to a better understanding of its biological characterization.

Ecological Security Pattern Construction in Loess Plateau Areas—A Case Study of Shanxi Province, China

Strong soil erosion and increasing human activities have made Loess Plateau areas ecologically fragile regions. Constructing the ecological security pattern (ESP) is imperative to maintain their ecosystem functions and sustainable development. However, it is still challenging to establish the ESP in such an unstable and scattered ecological environment. In this study, we take Shanxi Province, which suffers severe ecological problems in Loess Plateau areas, as an example to construct the ESP in a pattern of “source-resistance-corridor”. The proposed methods include the following steps: (1) potential ecological sources are selected with important ecosystem functions based on contributions of soil and water conservation, habitat quality, and carbon storage; (2) ecological sources are determined by considering core areas at the landscape scale based on morphological spatial pattern analysis (MSPA) along with stability based on dynamic assessment on previous sources; (3) the comprehensive resistance surface is constructed by multiple resistance factors and remotely sensed nighttime light data; (4) ecological corridors are simulated and extracted based on circuit theory. As a result, the proposed ESP in our study area mainly includes 13,592 km2 of ecological sources, 8519.64 km of ecological corridors, and 277 ecological nodes. Meanwhile, an ecological framework of “two axes, three belts, and three zones” was proposed based on the optimization and reorganization of ecological components within the ESP. Our research lays a methodological and practical foundation for regional ESP construction and sustainable development in Loess Plateau areas.

The effects of native seed mix composition and sowing density on plant community reassembly in wetlands

AbstractSeed‐based restoration of wetlands is often necessary to improve important ecosystem functions (e.g., invasion resistance and habitat provisioning) and meet society's need for wetland ecosystem services such as supporting recreational activities and improving water quality. However, persistent questions remain about the composition and sowing density of seed mixes needed to restore robust native wetland plant communities. In Great Salt Lake wetlands (Utah, USA), the revegetation of native species is crucial to recovering critical habitat and preventing reinvasion of the invasive, non‐native grass Phragmites australis and other invasive species (e.g., Typha spp.). In greenhouse and field experiments, we investigated the effects of seed mix composition and sowing density on plant community reassembly. We predicted that seed mixes containing native forb species with resource‐preempting traits (e.g., rapid seedling emergence and high aboveground growth rate) and high sowing densities (>5500 pure live seed m−2), would increase native plant light acquisition and establishment, thereby limiting invasive species. To our surprise, the effect of seed mix composition on native plant performance (cover and biomass) varied among the experiments, with distinct differences between plant functional groups arising. Native forb species had the highest performance in the greenhouse, but native grasses performed better in the field. Although multiple seed mix compositions show promise for establishing high native cover and biomass, these mixes may not always suppress invasive species. Interestingly, seed mix composition most often affected plant performance independent of sowing density. However, in one greenhouse experiment, we found that only slow‐growing mixes required a high sowing density to maximize native cover, an indication that the ideal sowing density may depend on the seed mix composition. Our research also supports the idea that in addition to reducing propagules of invasive species via appropriate management strategies, the application of higher sowing densities (>5500 pure live seed m−2) may lead to more favorable outcomes when a high density of invasive plant seeds remains or stressful field conditions are present. This research contributes to knowledge of plant community reestablishment in wetlands and demonstrates how seed‐based restoration strategies can catalyze native species revegetation and, in some situations, reduce the cover of invasive species.

Field collections and environmental DNA surveys reveal topographic complexity of coral reefs as a predictor of cryptobenthic biodiversity across small spatial scales

AbstractCoral reefs represent some of the most biodiverse ecosystems in the world but are currently undergoing large‐scale degradation due to anthropogenic stressors. Such degradation usually begins with coral bleaching, and if the stress condition is inflicted for too long may eventually result in loss of structural complexity (or “flattening”) of the reef, dramatically changing habitat availability for reef‐associated fauna. Despite having been linked to important ecosystem functions, cryptobenthic organisms are often overlooked in ecological monitoring programs, and their microhabitat dependencies are poorly understood. Here, we combined collection‐based biodiversity monitoring techniques with five different environmental DNA (eDNA) sampling techniques (Reef water, sediment, crevice water, slurp gun, and bulk sediment) to survey cryptobenthic fishes and annelids on a Maldivian fringing coral reef. Collectively, 176 fish and 140 annelid taxa were detected with eDNA across 14 surveyed sites, more than doubling the reported annelid taxa in the region with 88 new occurrences. Water filtered near the reef structure revealed the highest species richness out of the five eDNA sampling techniques tested. Furthermore, we found correlations between fish species richness and topographic complexity for both collection‐ and eDNA‐based techniques. This suggests that detection by eDNA may be linked to site‐specific predictors and reveal community differences across small spatial scales (tens of meters). We also report that reef flattening (going from structural complex to less complex sites) can cause a 50% reduction in fish diversity and that cryptobenthic fish species richness was highly associated with branching corals. In contrast, annelid communities showed no clear correlations with environmental predictors, but co‐amplification of non‐target, non‐annelid taxa may have distorted such correlations if present. This suggest that the predictive powers of eDNA for environmental gradients may be dependent on the targeted taxa.

“Hidden” biodiversity: a new amphipod genus dominates epifauna in association with a mesophotic black coral forest

AbstractBlack corals are important components of mesophotic and deep-water marine habitats. Their presence at great depths (e.g., 50 to 200 m) makes accessibility difficult, limiting our understanding of the associated biodiversity. Amphipods dominate vagile epifauna in marine habitats around the world, fulfilling important ecosystem functions. However, there are no studies on amphipods exclusively associated with black corals, including relationships between their ecological patterns (e.g., abundances) and the size of coral colonies. We investigated the epifaunal composition and abundance associated with black coral colonies of Antipathella wollastoni in the subtropical eastern Atlantic Ocean. In total, 1,736 epifaunal individuals were identified, of which 1,706 (98.27%) were amphipods, belonging to 6 taxa. We identified and described a new amphipod genus and species within the Stenothoidae family, Wollastenothoe minuta gen. nov., sp. nov., which outnumbered the amphipod assemblage (86.15%) and provided a complete taxonomic key of Stenothoidae family including this new finding. For the first time, the association between an amphipod species and a black coral was described, including a strong correlation between coral colony size and amphipod abundances. This study demonstrates that epifauna associated with mesophotic black corals remains largely undescribed.

Polyester microfiber impacts on coastal sediment organic matter consumption

As plastic pollution continues to accumulate at the seafloor, concerns around benthic ecosystem functionality heightens. This research demonstrates the systematic effects of polyester microfibers on seafloor organic matter consumption rates, an important benthic ecosystem function connected to multiple reactions and processes. We used a field-based assay to measure the loss of organic matter, both with and without polyester microfiber contamination. We identified sediment organic matter content, mud content, and mean grain size as the main drivers of organic matter consumption, however, polyester microfiber contamination decoupled ecosystem relationships and altered observed organic matter cycling dynamics. Organic matter consumption rates varied across horizontal and vertical spaces, highlighting that consumption and associated plastic effects are dependent on environmental heterogeneity at both small (within sites) and larger (between sites) scales. Our results emphasize the important role habitat heterogeneity plays in seafloor organic matter consumption and the associated effects of plastic pollution on ecosystem function.

Soil prokaryotic and fungal biome structures associated with crop disease status across the Japan Archipelago.

Archaea, bacteria, and fungi in the soil are increasingly recognized as determinants of agricultural productivity and sustainability. A crucial step for exploring soil microbiomes with important ecosystem functions is to perform statistical analyses on the potential relationship between microbiome structure and functions based on comparisons of hundreds or thousands of environmental samples collected across broad geographic ranges. In this study, we integrated agricultural field metadata with microbial community analyses by targeting 2,903 bulk soil samples collected along a latitudinal gradient from cool-temperate to subtropical regions in Japan (26.1-42.8 °N). The data involving 632 archaeal, 26,868 bacterial, and 4,889 fungal operational taxonomic units detected across the fields of 19 crop plant species allowed us to conduct statistical analyses (permutational analyses of variance, generalized linear mixed models, randomization analyses, and network analyses) on the relationship among edaphic factors, microbiome compositions, and crop disease prevalence. We then examined whether the diverse microbes form species sets varying in potential ecological impacts on crop plants. A network analysis suggested that the observed prokaryotes and fungi were classified into several species sets (network modules), which differed substantially in association with crop disease prevalence. Within the network of microbe-to-microbe coexistence, ecologically diverse microbes, such as an ammonium-oxidizing archaeon, an antibiotics-producing bacterium, and a potentially mycoparasitic fungus, were inferred to play key roles in shifts between crop-disease-promotive and crop-disease-suppressive states of soil microbiomes. The bird's-eye view of soil microbiome structure will provide a basis for designing and managing agroecosystems with high disease-suppressive functions.IMPORTANCEUnderstanding how microbiome structure and functions are organized in soil ecosystems is one of the major challenges in both basic ecology and applied microbiology. Given the ongoing worldwide degradation of agroecosystems, building frameworks for exploring structural diversity and functional profiles of soil microbiomes is an essential task. Our study provides an overview of cropland microbiome states in light of potential crop-disease-suppressive functions. The large data set allowed us to explore highly functional species sets that may be stably managed in agroecosystems. Furthermore, an analysis of network architecture highlighted species that are potentially used to cause shifts from disease-prevalent states of agroecosystems to disease-suppressive states. By extending the approach of comparative analyses toward broader geographic ranges and diverse agricultural practices, agroecosystem with maximized biological functions will be further explored.

Designing marine infrastructure to restore native shellfish

ABSTRACT Reef forming bivalves like mussels and oysters have undergone massive declines due to many factors including increasing habitat loss. Bivalves provide important ecosystem functions and services that include increasing biodiversity and providing sustenance and cultural services to humans. Therefore, it is vital to preserve the reefs that remain and restore those that have been damaged or lost. Some of this natural habitat has been lost to coastal development making full habitat restoration near impossible. However, targeting habitat building bivalves in restoration efforts and designing marine infrastructure to attract bivalves, is a way to preserve and increase biodiversity in lost or degraded ecosystems. There is an increasing number of tools to enhance the effectiveness of restoration efforts including, designing infrastructure to mitigate external environmental stressors, and better understanding the habitat requirements and stressors of the species being restored. With the rapid loss of the world’s ecosystems, increasing research suggests restoration approaches are not one-size-fits-all and efforts are the most effective when tailored to local environmental conditions and species.

Agriculture-driven deforestation in Ecuador's Mache-Chindul Ecological Reserve: The farmers' perspective

Tropical rainforests serve as invaluable global carbon stocks with long-term climate mitigation potential and important ecosystem functions and biodiversity. Recent scholarship has identified agriculture as the main driver of tropical rainforest deforestation worldwide, yet effective policy action needs to understand why farmers continue to clear land, beyond broad-brush attributions of blame. This study highlights the constellation of social forces that drive deforestation in a subsection of the Mache Chindul Ecological Reserve (REMACH) in northwest Ecuador. Rather than simply assuming that farmers are either indifferent to or ignorant of the effects of deforestation, we highlight the perspective of farmers themselves as they reflect on, both, their relationship with other key actors and the broader contextual factors informing their own land-use decisions. We surveyed 70 rural households using a 45-question data collection tool, conducted semi-structured interviews with key stakeholders such as local conservation practitioners and community elders, employed participant observation and reviewed government documents.We find that colonist farmers who live in and around the REMACH clear land because they view doing so as their most reliable means of securing a livelihood for themselves and their children in a context of political and economic hardship and uncertainty. A history of government incentives to clear land, a deeply ambiguous land tenure system, and a sudden influx of externally-funded conservation NGOs to the region have all contributed to exclude farmers from the decision-making process, while simultaneously exacerbating the conditions that make deforestation farmers' most practical option—despite their awareness of its environmental impact. The data underscore that locals are, in fact, highly invested in the idea of conserving a healthy environment for future generations, but are nonetheless driven to act against this interest by their own precarity. By helping governmental and non-governmental conservation practitioners better understand farmers’ land-use decisions, the study reframes the latter group not as the problem, but as vital future partners.

A comparison of two gene regions for assessing community composition of eukaryotic marine microalgae from coastal ecosystems

Two gene regions commonly used to characterise the diversity of eukaryotic communities using metabarcoding are the 18S ribosomal DNA V4 and V9 gene regions. We assessed the effectiveness of these two regions for characterising diverisity of coastal eukaryotic microalgae communities (EMCs) from tropical and temperate sites. We binned amplicon sequence variants (ASVs) into the high level taxonomic groups: dinoflagellates, pennate diatoms, radial centric diatoms, polar centric diatoms, chlorophytes, haptophytes and ‘other microalgae’. When V4 and V9 generated ASV abundances were compared, the V9 region generated a higher number of raw reads, captured more diversity from all high level taxonomic groups and was more closely aligned with the community composition determined using light microscopy. The V4 region did resolve more ASVs to a deeper taxonomic resolution within the dinoflagellates, but did not effectively resolve other major taxonomic divisions. When characterising these communities via metabarcoding, the use of multiple gene regions is recommended, but the V9 gene region can be used in isolation to provide high-level community biodiversity to reflect relative abundances within groups. This approach reduces the cost of sequencing multiple gene regions whilst still providing important baseline ecosystem function information.

Coral restoration can drive rapid reef carbonate budget recovery

Restoration is increasingly seen as a necessary tool to reverse ecological decline across terrestrial and marine ecosystems.1,2 Considering the unprecedented loss of coral cover and associated reef ecosystem services, active coral restoration is gaining traction in local management strategies and has recently seen major increases in scale. However, the extent to which coral restoration may restore key reef functions is poorly understood.3,4 Carbonate budgets, defined as the balance between calcium carbonate production and erosion, influence a reef's ability to provide important geo-ecological functions including structural complexity, reef framework production, and vertical accretion.5 Here we present the first assessment of reef carbonate budget trajectories at restoration sites. The study was conducted at one of the world's largest coral restoration programs, which transplants healthy coral fragments onto hexagonal metal frames to consolidate degraded rubble fields.6 Within 4 years, fast coral growth supports a rapid recovery of coral cover (from 17%± 2% to 56%± 4%), substrate rugosity (from 1.3± 0.1 to 1.7± 0.1) and carbonate production (from 7.2± 1.6 to 20.7± 2.2kg m-2 yr-1). Four years after coral transplantation, net carbonate budgets have tripled and are indistinguishable from healthy control sites (19.1± 3.1 and 18.7± 2.2kg m-2 yr-1, respectively). However, taxa-level contributions to carbonate production differ between restored and healthy reefs due to the preferential use of branching corals for transplantation. While longer observation times are necessary to observe any self-organization ability of restored reefs (natural recruitment, resilience to thermal stress), we demonstrate the potential of large-scale, well-managed coral restoration projects to recover important ecosystem functions within only 4 years.

River network‐scale drying impacts the spatiotemporal dynamics of greenhouse gas fluxes

AbstractRivers significantly contribute to global biogeochemical cycles; however, we have a limited understanding of how drying may influence these cycles. Drying fragments river networks, thereby influencing important ecosystem functions such as the processing of carbon and nitrogen, and associated fluxes of greenhouse gases (GHGs) both locally, and at the river network scale. Our objective was to assess, using a network‐scale approach, the lateral, longitudinal, and temporal dynamics of GHG fluxes in a river network naturally fragmented by drying. We used a closed‐loop chamber with automated analyzers to measure carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes from dry sediments, flowing waters, isolated pools, and riparian soils, along with a suite of environmental variables, over 9 months at 20 sites across a non‐perennial river network in France. Network‐scale drying had a spatial and temporal legacy effect on GHG fluxes. On average, CO2 fluxes were up to 29 times higher from perennial than non‐perennial sites under flowing conditions. At non‐perennial sites, CO2 and N2O fluxes positively covaried with time since rewetting. In addition, CO2 and N2O fluxes at perennial sites positively covaried with the percent of non‐perennial reaches upstream, indicating a spatial effect of drying. GHG fluxes from riparian soil and dry riverbed sediments had markedly different magnitudes and covariates. This research demonstrates that drying not only has a local‐scale impact but also influences GHG fluxes at the network scale, contributing valuable insights for upscaling global riverine GHG estimates.

Carcass provisioning and intra-guild risk avoidance between two sympatric large carnivores

Apex carnivores that rely primarily on predation play a central but complex role within scavenging ecology by potentially suppressing intra-guild competitors, but also facilitating them by providing a reliable supply of carrion. We investigated the competitive relationship between sympatric wolves (Canis lupus) and wolverines (Gulo gulo) in Norway across three seasons. We deployed remote cameras at fresh wolf kills (n = 29) and built Bayesian generalized linear mixed models (GLMMs) to explore the use of fresh wolf-killed prey by sympatric wolves and wolverines. Our results showed that wolves facilitated wolverines by providing scavenging opportunities. Biomass available from wolf kills was influenced by seasonal wolf prey preference and group size. Wolverines visited 100% of wolf kills in fall and winter, whereas only 18% in summer. We found that in winter, wolverines visited wolf kills 3.6 and 6.7 times more often than single wolves and wolf groups revisited their kills, and spent 10 and 25 times as much time at carcasses compared to single wolves and groups of wolves. Thus, wolverines played an important role in the depletion of wolf-killed prey, with potential effects on the scavenging behavior of other guild members. Understanding how globally threatened top predators may function as key species in scavenging processes is important to conservation as this may have community-wide cascading effects and support important ecosystem functions and services.Significance statementLarge carnivores serve a central role within scavenging ecology through the suppression and facilitation of intraguild competitors. The wolf, as an apex obligate predator, can provide a reliable supply of carrion, that can serve as an important resource to facultative scavengers. However, while facultative behavior helps to mitigate the effects of limited prey for scavengers, it can also increase exposure to competition and intraguild predation. Across three seasons, we explored the use of fresh wolf-killed prey by sympatric wolves and wolverines. Our findings reveal that wolves facilitate wolverines by providing scavenging opportunities, where biomass available from kills is influenced by wolves’ prey preference and group size. Wolverines, like wolves, utilized kills heavily during winter, when increased access to food is important to wolverine reproductive rates. Wolverines exhibited caching behavior, possibly reducing exposure to interspecific competition, while serving an important role in the depletion of carrion biomass.

Forest structure and heterogeneity increase diversity and alter composition of host–parasitoid networks

Abstract Antagonistic host–parasitoid interactions can be quantified using bipartite and metanetworks, which have the potential to reveal how habitat structural elements relate to this important ecosystem function. Here, we analysed the host–parasitoid interactions of cavity‐nesting bees and wasps, as well as their abundance, diversity and species richness with forest structural elements from 127 forest research plots in southwestern Germany. We found that parasitoid abundance, diversity and species richness all increase with host abundance, a potential mediator between parasitoids and forest structure. Both parasitoid abundance and diversity increased with stand structural complexity, possibly mediated by the abundance of hosts. In addition, parasitoid abundance increased with increasing standing deadwood and herb cover. The bipartite networks of host–parasitoid interactions showed higher connectance with increasing standing deadwood, herb cover and host abundance. Analyses of interactions within the host–parasitoid metanetwork revealed that increasing host abundance and decreasing canopy cover diversify the suites of interactions present at the plot level. These results demonstrate that forest structural elements can improve the stability and resilience of host–parasitoid networks by promoting parasitoids and diversifying interactions in ecological networks.

Alkaline-modified biochar and nitrifying microbiome synergistically mitigate the toxicity of oxytetracycline and its toxic by-products

The widely used antibiotic oxytetracycline (OTC) is found in various natural and engineered water environments, where it can potentially disrupt important ecosystem functions such as nitrification. This work proposed the use of alkaline-pretreated biochar (BC) with a nitrifying microbiome to mitigate OTC disturbance and enhance the removal and detoxification of both OTC and its by-products (BPs). The OTC adsorption capacity of BC was pre-optimized using a 1 M NaOH solution. While exposure to OTC led to the replacement of the dominant sub-species populations within Nitrosomonas, the addition of BC preserved the original diversity and structure of the nitrifying microbiome. The evaluation of long-term reactor operation and batch tests using advanced analytical methods revealed that the addition of BC significantly increased the removal of OTC with a novel biotransformation pathway. Structure-based toxicity modeling and antimicrobial susceptibility experiments were performed to assess the toxicity of OTC, its BPs, and bulk effluent containing both OTC and its known/unknown BPs. Three OTC BPs were found to have 6–90 times higher toxicity than OTC itself. In comparison to the microbiome alone, the addition of BC had the potential to enhance the detoxification of both OTC and its BPs. Collectively, the results of the present study indicate that the addition of BC to nitrifying systems may be a promising retrofitting option that proactively maintains the biological function and stability of the system in the presence of toxic waste streams via the synergistic control of both the original contaminants and their BPs in conjunction with nitrifying microbiomes.

Feeding kinematics of a surgeonfish reveal novel functions and relationships to reef substrata

Biting to obtain attached benthic prey characterizes a large number of fish species on coral reefs, and is a feeding mode that contributes to important ecosystem functions. We use high-speed video to reveal the mechanisms used by a surgeonfish, Acanthurus leucosternon, to detach algae. After gripping algae in its jaws, the species pulls it by ventrally rotating both the head and the closed jaws, in a novel use of the intra-mandibular joint. These motions remain in the plane of the fish, reducing the use of a lateral head flick to detach the algae. The novel ability to bite and pull algae off the substrate without bending the body laterally minimizes exposure to high water flows, and may be an adaptation to feeding in challenging reef habitats such as the crest and flat. Therefore, our results could potentially represent a key milestone in the evolutionary history of coral reef trophodynamics.

Grazing-driven shifts in soil bacterial community structure and function in a typical steppe are mediated by additional N inputs

Herbivore grazing and nitrogen (N) fertilization affect soil microbial diversity and community composition both in direct and indirect pathways (e.g., via alterations in soil microenvironment and plant communities); however, their combination effects are still largely unexplored. We carried out a field study to investigate how soil abiotic properties, plant community composition and functional traits altered soil bacterial community structure and function in response to a long-term herbivore grazing (17-year sheep grazing with four stocking rates) and anthropogenic N inputs (6-year N addition with four levels) experiment. We show that a high stocking rate of 8.7 sheep ha−1 (SR8.7) decreased soil bacterial α- and β-diversity, while α- and β-diversity showed hump-shaped and saddle-shaped responses, respectively, with increasing N addition rate, reaching tipping points at the N application rate of 10 g N m−2 year−1 (N10). The synergistic effects of grazing and N addition induced the highest soil bacterial α-diversity at SR2.7 with N10. The contrasting effects of grazing and N addition induced higher soil bacterial β-diversity at SR8.7 with N20. Plant factors (e.g., aboveground biomass of Stipa bungeana and community-weighted mean carbon [CWM_C]), edaphic factors (e.g., soil moisture, pH, NO3−-N, and C:nutrients ratios) and their interactions were the most significant factors affecting the diversity and community composition of bacteria. Our structure equation model (SEM) shows that grazing-induced negative effects on soil pH and plant community composition indirectly increased the β-diversity of soil bacteria, while grazing-induced decreased CWM_C had positive effects on bacterial α-diversity and community structure. However, N addition indirectly increased β-diversity of soil bacteria via changes in soil NO3−-N and plant community composition, while N addition had negative impacts on bacterial α-diversity and community structure via variations in CWM_C. The interaction of grazing and N addition increased the complexity and stability of the bacterial network. Based on the KEGG database, grazing and N addition could accelerate the soil functional potential of C and N cycling. Our findings suggest that N application at a rate of <10 g N m−2 year−1 with a stocking rate of <5.3 sheep ha−1 could maintain the development of soil bacteria in supporting the most important ecosystem functions and services. Complex responses of soil microbes to grazing and N addition indicate the need for deeper investigations of the impacts of global change on microbial involvement in biogeochemical cycles.

Pollinator-mediated effects of landscape-scale land use on grassland plant community composition and ecosystem functioning - seven hypotheses.

Environmental change is disrupting mutualisms between organisms worldwide. Reported declines in insect populations and changes in pollinator community compositions in response to land use and other environmental drivers have put the spotlight on the need to conserve pollinators. While this is often motivated by their role in supporting crop yields, the role of pollinators for reproduction and resulting taxonomic and functional assembly in wild plant communities has received less attention. Recent findings suggest that observed and experimental gradients in pollinator availability can affect plant community composition, but we know little about when such shifts are to be expected, or the impact they have on ecosystem functioning. Correlations between plant traits related to pollination and plant traits related to other important ecosystem functions, such as productivity, nitrogen uptake or palatability to herbivores, lead us to expect non-random shifts in ecosystem functioning in response to changes in pollinator communities. At the same time, ecological and evolutionary processes may counteract these effects of pollinator declines, limiting changes in plant community composition, and in ecosystem functioning. Despite calls to investigate community- and ecosystem-level impacts of reduced pollination, the study of pollinator effects on plants has largely been confined to impacts on plant individuals or single-species populations. With this review we aim to break new ground by bringing together aspects of landscape ecology, ecological and evolutionary plant-insect interactions, and biodiversity-ecosystem functioning research, to generate new ideas and hypotheses about the ecosystem-level consequences of pollinator declines in response to land-use change, using grasslands as a focal system. Based on an integrated set of seven hypotheses, we call for more research investigating the putative pollinator-mediated links between landscape-scale land use and ecosystem functioning. In particular, future research should use combinations of experimental and observational approaches to assess the effects of changes in pollinator communities over multiple years and across species on plant communities and on trait distributions both within and among species.

Identifying microbiota community patterns important for plant protection using synthetic communities and machine learning

Plant-associated microbiomes contribute to important ecosystem functions such as host resistance to biotic and abiotic stresses. The factors that determine such community outcomes are inherently difficult to identify under complex environmental conditions. In this study, we present an experimental and analytical approach to explore microbiota properties relevant for a microbiota-conferred host phenotype, here plant protection, in a reductionist system. We screened 136 randomly assembled synthetic communities (SynComs) of five bacterial strains each, followed by classification and regression analyses as well as empirical validation to test potential explanatory factors of community structure and composition, including evenness, total commensal colonization, phylogenetic diversity, and strain identity. We find strain identity to be the most important predictor of pathogen reduction, with machine learning algorithms improving performances compared to random classifications (94-100% versus 32% recall) and non-modelled predictions (0.79-1.06 versus 1.5 RMSE). Further experimental validation confirms three strains as the main drivers of pathogen reduction and two additional strains that confer protection in combination. Beyond the specific application presented in our study, we provide a framework that can be adapted to help determine features relevant for microbiota function in other biological systems.

Rhizoid-associated cyanobacteria are the main contributors to biological nitrogen fixation in restored moss crust

Biological soil crusts (biocrusts) are associations of highly specialized communities and topsoil particles and play important ecosystem functions in drylands. Biotic interactions affected the assemblage of biocrust communities and thus their ecological function and adaption abilities. As the dominant organism in the moss crust, moss plays a significant role in modifying the microenvironment and releasing carbon, and this may affect the distribution and metabolic activity of diazotrophic cyanobacteria, which are the dominant diazotrophs. In this study, we examined the contribution of diazotrophic cyanobacteria to nitrogenase activity (NA) by investigating the NA under different light conditions and estimated the proportion of diazotrophic cyanobacteria from total diazotrophs. We tested the spatial distribution of cyanobacteria using laser confocal fluorescence microscopy (CLSM). Additionally, we separated diazotrophs in moss crust into free-living and moss-associated diazotrophs and compared the NA, nifH gene abundances and their transcripts, and the community composition of free-living and moss-associated diazotrophs. The light-dependent characteristic of NA and dominance of heterocystous cyanobacteria (accounting for over 90% of total nifH sequences at both the DNA and transcript levels) suggested a significant contribution of heterocystous cyanobacteria to NA. Cyanobacteria were mainly distributed in a few millimeters of subsoil in which abundant cyanobacteria were associated with moss rhizoids. The NA rates of moss-associated diazotrophs were comparable to those of moss crust and approximately 4–8 times higher than those of free-living diazotrophs, indicating the major role of moss-associated diazotrophs in nitrogen fixation. The community composition of moss-associated diazotrophs was similar to that of free-living diazotrophs. Moss-associated diazotrophs have a higher NA per copy of the nifH gene and transcript than free-living diazotrophs, proving the synergistic association of moss and cyanobacteria with NA.