Marsh Communities Research Articles

Importance of eukaryotes in shaping microbial benthic communities in Charente-maritime marshes, France.

Marshes are wetlands known for providing major ecosystem services in terms of water quality and human activities. These ecosystem services are mainly provided by marshes' benthic community, composed of prokaryotes (bacteria and archaea) but also of eukaryotes (micro-eukaryotes and meiofauna). The aim of this study is to (1) assess the environmental parameters affecting benthic community composition in marshes, (2) highlight the associations between organisms from the three domains of life, and (3) determine the parameters controlling these associations. Hence, benthic communities of eight different marshes from three typologies (salted, brackish and freshwater) and four seasons (autumn 2020, spring 2021, summer 2021 and autumn 2021) were assessed. This study revealed three main drivers of community composition. First, salinity drives the community composition illustrated by the differences observed between the three typologies of marshes. Relative abundance of Nitrososphaeria, Halobacteria, Bacillariophyceae, Conoidasida and nematodes increased with salinity while methanogenic archaea, Chlorophyceae and copepod's relative abundance decreased. The second driver is the physical-chemistry of the site, particularly nutrients. The season is the last driver of community composition, seasonal pattern varying for each site within a typology. LEfSe analyses defined biomarkers of typology and season, among which many prokaryotes involved in the nitrogen cycle and photosynthetic micro-eukaryotes where present in different co-occurrence networks, highlighting the importance of nitrogen cycle in marshes. Co-occurrence networks revealed several connections between organisms of the three domains of life, particularly between prokaryotes and photosynthetic eukaryotes. This study illustrates thus the importance of holistic approaches in microbial ecology for revealing a comprehensive view of the whole microbial interactions occurring in complex ecosystems.

Topological differentiation of vegetation of the Lublin-Volyn geobotanical district

The position of the Lublin and Volyn (Volhynian) uplands within the geobotanical zonation system is ambiguous and disputable. An analysis of the syntaxonomical diversity and landscape distribution of the egetation of the Lublin and Volyn uplands revealed their similarity, and we consider this whole territory as the Lublin-Volyn geobotanical district of hornbeam-oak, oak forests, and steppe meadows. This district differs from the adjacent territories and is classified within the Central European mixed forests ecoregion. Typical and diagnostic syntaxa have been identified, and ecological-coenotic profiles have been constructed to characterize the distribution patterns of shrub-forest and herbaceous vegetation within the landscape. Based on calculations of phytosociological indicators for the main ecological factors, graphical patterns of their variation were developed. It was determined that the characteristic forests of the district, Tilieto-Carpinetum (Carpinion betulis), are represented by four variants (T.-C. var. galeobdolosum; T.-C. var. hepaticosum; T.-C. var. caricosum pilosae; T.-C. var. isopyrosum). The district is also characterized by the presence of syntaxa associated with carbonate soils, both of the marsh type (Caricion davallianae) and the meadow-steppe type (Cirsio-Brachypodion, Festucion valesiacae), with the dominance of Carex humilis and Stipa capillata. Using DCA-analysis, the correlation between ecological factor indicators and the distribution of plant communities within the ecological space has been established, forming six fields distributed along three vectors: by moisture (aquatic and marsh communities), xerophytism, and chemical properties of soils (meadow-steppe communities), as well as the structure of coenoses with a specific ombroregime (forest communities).

Variable Effects of Experimental Sea-level Rise Conditions and Invasive Species on California Cordgrass

Sea-level rise (SLR) will produce unprecedented changes in tidal marsh systems that already cope with daily tidal fluctuation, disturbances from storms, and salinity changes from droughts and runoff events. Additionally, negative impacts from non-native invasive species may alter marsh plants’ ability to respond to SLR stressors like increased inundation and salinity. Increasingly, tidal marsh communities must tolerate both changes in the physical environment from SLR and increased risk of invasion by non-native species. To assess the response of a threatened tidal marsh cordgrass (Spartina foliosa) to both stressors, we implemented a field experiment in San Francisco Bay, CA, USA, exposing cordgrass to a treatment that extended tidal inundation projected with SLR using a recently developed in situ method. At one of two field sites, we also enclosed the cordgrass with or without the invasive European green crab, Carcinus maenas. We found that cordgrass responded negatively to longer inundation, although these effects varied by site and year. In higher inundation treatments, cordgrass survival increased with increasing surface elevation of the plot. Cordgrass survival was lower in the presence of invasive green crabs relative to controls. We did not find interacting effects of responses to increased inundation and invasive species presence, which highlights the need to consider how latent or sequential effects of multiple stressors may affect ecosystems. This study demonstrates significant biological responses to invasive species presence and increased inundation. Evaluating relative effects and timing of multiple stressors, especially those induced by climate change and invasive species, will help us to manage threatened ecological communities in a changing world.

Machine Learning Predictions of Vertical Accretion in the Mississippi River Deltaic Plain

AbstractDeltaic landscapes consist of vast wetland systems that rely on sedimentation to maintain their elevation and ecological communities against relative sea‐level rise. In the Mississippi River Deltaic plain, rising relative sea level and anthropogenic activities are causing land loss that will continue unless vertical accretion of sediment on the wetland surface is enough to fill the accommodation space. Even though the fate of the Mississippi Deltaic plain is tied directly to vertical accretion, there is not yet a clear understanding of the system‐wide controls on this process. Here, we investigate vertical accretion in coastal Louisiana using a data set of 266 stations from the Coastwide Reference Monitoring System (CRMS). Using linear regression models, we analyze vertical accretion in freshwater‐intermediate, brackish, and saline marsh communities. Integrating results from these models into a Gaussian Process regression model, we predict controls on vertical accretion rates across the deltaic plain. Consistent with previous studies, our results suggest that tidal amplitude and flood depth are critical controls on vertical accretion. These effects are additive and marshes with high tidal amplitudes and flood depths experience the most vertical accretion. Interestingly, the normalized difference vegetation index is found to be important for predicting vertical accretion, but not because of an increase in biomass production, but because it records unique marsh communities and flooding regimes. This study emphasizes the importance of incorporating marsh specific information into predictive models for the vertical accretion of coastal wetlands and that better predictions of wetland accretion probably require denser observational data.

Contribution of soil seed banks to vegetation resilience in coastal freshwater wetlands of subtropical Australia

AbstractQuestionsWhat role do soil seed banks play in the resilience of coastal freshwater wetland vegetation communities? How might soil seed bank composition and similarity to standing vegetation drive changes in vegetation expression, particularly given projected changes in climate?LocationSixty wooded coastal freshwater wetlands in southeast Queensland, Australia.MethodsWe surveyed standing vegetation and investigated soil seed bank composition through an 8‐month‐long emergence experiment.ResultsSoil seed bank assemblages were dominated by forb and sedge species (23% exotic), but composition varied throughout the study region. Spatial (north–south) and land‐use (urban–rural) gradients explained some variation in soil seed bank composition. Soil moisture and groundwater dependence also influenced species distributions, particularly for freshwater wetland species. The similarity of soil seed banks to standing vegetation was low. Species present in both extant and soil seed bank assemblages were commonly native wetland taxa, including one salt marsh species (Juncus kraussii).ConclusionsProjected climatic changes will likely drive changes in coastal freshwater wetland vegetation communities through increases in the frequency and intensity of disturbances (e.g., storm surge). Our results suggest that regeneration from soil seed banks could promote four potential scenarios: (1) expansion of weed communities, (2) expansion of salt marsh communities, (3) maintenance and expansion of wetland/terrestrial species, and (4) transformation to an unvegetated open water zone because of reduced regeneration success under changing conditions. These diverse vegetation futures highlight the vulnerability of wooded coastal freshwater wetlands and the need for research and management interventions to maintain their biodiversity and ecosystem services.

Mapping the tidal marshes of coastal Virginia: a hierarchical transfer learning approach

ABSTRACT Coastal wetlands, especially tidal marshes, play a crucial role in supporting ecosystems and slowing shoreline erosion. Accurate and cost-effective identification and classification of various marsh types, such as high and low marshes, are important for effective coastal management and conservation endeavors. However, mapping tidal marshes is challenging due to heterogeneous coastal vegetation and dynamic tidal influences. In this study, we employ a deep learning segmentation model to automate the identification and classification of tidal marsh communities in coastal Virginia, USA, using seasonal, publicly available satellite and aerial images. This study leverages the combined capabilities of Sentinel-2 and National Agriculture Imagery Program (NAIP) imagery and a UNet architecture to accurately classify tidal marsh communities. We illustrate that by leveraging features learned from data abundant regions and small quantities of high-quality training data collected from the target region, an accuracy as high as 88% can be achieved in the classification of marsh types, specifically high marsh and low marsh, at a spatial resolution of 0.6 m. This study contributes to the field of marsh mapping by highlighting the potential of combining multispectral satellite imagery and deep learning for accurate and efficient marsh type classification.

Establishing peat-forming plant communities: A comparison of wetland reclamation methods in Alberta's oil sands region.

The Sandhill Wetland (SW) and Nikanotee Fen (NF) are two wetland research projects designed to test the viability of peatland reclamation in the Alberta oil sands post-mining landscape. To identify effective approaches for establishing peat-forming vegetation in reclaimed wetlands, we evaluated how plant introduction approaches and water level gradients influence species distribution, plant community development, and the establishment of bryophyte and peatland species richness and cover. Plant introduction approaches included seeding with a Carex aquatilis-dominated seed mix, planting C. aquatilis and Juncus balticus seedlings, and spreading a harvested moss layer transfer. Establishment was assessed 6 years after the introduction at SW and 5 years after the introduction at NF. In total, 51 species were introduced to the reclaimed wetlands, and 122 species were observed after 5 and 6 years. The most abundant species in both reclaimed wetlands was C. aquatilis, which produced dense canopies and occupied the largest water level range of observed plants. Introducing C. aquatilis also helped to exclude marsh plants such as Typha latifolia that has little to no peat accumulation potential. Juncus balticus persisted where the water table was lower and encouraged the formation of a diverse peatland community and facilitated bryophyte establishment. Various bryophytes colonized suitable areas, but the moss layer transfer increased the cover of desirable peat-forming mosses. Communities with the highest bryophyte and peatland species richness and cover (averaging 9 and 14 species, and 50%-160% cover respectively) occurred where the summer water level was between -10 and -40 cm. Outside this water level range, a marsh community of Typha latifolia dominated in standing water and a wet meadow upland community of Calamagrostis canadensis and woody species established where the water table was deeper. Overall, the two wetland reclamation projects demonstrated that establishing peat-forming vascular plants and bryophytes is possible, and community formation is dependent upon water level and plant introduction approaches. Future projects should aim to create microtopography with water tables within 40 cm of the surface and introduce vascular plants such as J. balticus that facilitate bryophyte establishment and support the development of a diverse peatland plant community.

Changing processes flooding a salt marsh in a microtidal estuary with a drying climate

Estuarine salt marshes globally face numerous threats, not least of which include changing hydrological conditions from human alteration and climate change impact to river flows, sea levels and coastal processes. While changing inundation is evident in many systems, often, the detail of which estuarine processes are changing and to what extent they contribute to flooding and habitat distribution remains unknown. Water levels in the microtidal Swan River Estuary (Derbarl Yerrigan), Western Australia, which has experienced significant climate drying since the 1970's, were disaggregated to assess contributions from tides, mean sea level, barometric effects, river flows and river-tide interactions. These contributions were mapped to the habitat of a salt marsh community. The effect of declining river flows on tides were further assessed by wavelet and harmonic analyses. We found that tides and barometric effects presently dominate flooding events of relevance to the salt marsh community. Declining winter runoff resulted in an increase in the tidal amplitude in the upper estuary. There was also a positive winter mean sea level pressure trend, associated with the winter rainfall decline. Altogether, there was zero net change to flooding of a salt marsh in the estuary from these processes. Therefore, steady sea level rise masked changes in the relative contribution of flooding mechanisms in the estuary which have implications for the stability of the marsh ecosystem. Disaggregating process contributions to salt marsh water levels offers a means to better assess the hydrodynamic processes presently sustaining salt marsh communities and to inform how they might change in the future. These results show that numerous hydrological processes can interact to mask non-stationary changes to estuarine hydrology supporting salt marsh habitat.

Coastal vegetation responses to large dam removal on the Elwha River

IntroductionLarge dam removals provide a restoration opportunity for shrinking coastal wetland habitats. Dam removal can increase sediment delivery to sediment-starved river deltas and estuaries by restoring natural sediment transport and mobilizing reservoir-impounded sediment. However, rapid mobilization of massive quantities of sediment stored behind large dams also constitutes a major ecological perturbation. Information is lacking on coastal habitat responses to sediment pulses of this magnitude.MethodsRemoval of two large dams along the Elwha River (Washington, USA) in 2011–2014 released ~20.5 Mt of impounded sediment, ~5.4 Mt of which were deposited in the delta and estuary (hereafter, delta). We used time series of aerial imagery, digital elevation models, and vegetation field sampling to examine plant community responses to this sediment pulse across seven years during and after dam removal.ResultsBetween 2011 and 2018, the Elwha River delta increased by ~26.8 ha. Vegetation colonized ~16.4 ha of new surfaces, with mixed pioneer vegetation on supratidal beach, river bars, and river mouth bars and emergent marsh vegetation in intertidal aquatic habitats. Colonization occurred on surfaces that were higher and more stable in elevation and farther from the shoreline. Compared to established delta plant communities, vegetation on new surfaces had lower cover of dominant species and functional groups, with very low woody cover, and lower graminoid cover than dunegrass and emergent marsh communities. Over time following surface stabilization, however, vegetation on new surfaces increased in species richness, cover, and similarity to established communities. By 2018, ~1.0 ha of vegetation on new surfaces had developed into dunegrass or willow–alder communities and ~5.9 ha had developed into emergent marsh. At the same time, dam removal had few discernible effects on established delta plant communities.DiscussionTogether, these results suggest that rapid sediment mobilization during large dam removal has potential to expand coastal wetland habitat without negatively affecting established plant communities. However, as sediment loads declined in 2016–2018, new delta surfaces decreased by ~4.5 ha, and ~1.6 ha of new vegetation reverted to no vegetation. Long-term persistence of the expanded coastal habitat will depend on ongoing erosional and depositional processes under the restored natural sediment regime.

Effects of grazing prohibition on nirK- and nirS-type denitrifier communities in salt marshes.

Grazing prohibition is an effective management practice to restore salt marsh functioning. However, the effects of grazing exclusion on denitrifying microbial communities and their controlling factors in salt marshes remain unclear. In this study, we surveyed soil physicochemical properties and above- and below-ground biomass and using quantitative polymerase chain reaction and Illumina MiSeq high-throughput sequencing technology to determine the relative abundance, composition, and diversity of nitrite reductase nirS- and nirK-type denitrifying bacterial communities associated with grazing prohibition treatments and elevations. The abundance of nirS-type denitrifiers increased with grazing prohibition time, whereas the abundance of nirK-type denitrifiers remained unaltered. Moreover, nirS-type denitrifiers were more abundant and diverse than nirK-type denitrifiers in all treatments. Grazing prohibition significantly altered the operational taxonomic unit richness, abundance-based coverage estimator, and Chao1 indices of the nirS-type denitrifying bacterial communities, whereas it only minimally affected the structure of the nirK-type denitrifying bacterial community. The results imply that the nirS community, rather than nirK, should be the first candidate for use as an indicator in the process of salt marsh restoration after grazing prohibition. Substances of concern, total nitrogen, and salinity were the key environmental factors affecting the abundance and community composition of nirS and nirK denitrifiers. The findings of this study provide novel insights into the influence of the length of grazing prohibition and elevation on nirS- and nirK-type denitrifying bacterial community composition in salt marshes.

Distribution and trophic functioning of planktonic communities in coastal marshes in Atlantic Coast of France

Coastal marshes are submitted to huge management due to anthropogenic pressure and thus, it is essential to preserve their biodiversity, their ecological functions and the ecosystem services they can provide. This study investigates the diversity and abundance of planktonic communities (heterotrophic prokaryotes, heterotrophic protists, microphytoplankton and metazooplankton). The aim of this study is to provide a first quantitative inventory on the plankton communities present in two marshes and to construct the different typologies of planktonic food webs in these marshes. Seasonal samplings (4) for environmental variables, nutrient concentrations and planktonic communities were conducted at 2–3 stations on each marsh during a year. A total of five different types of planktonic food web were determined, three of them were found in both marshes. The saltmarsh phytoplanktonic communities were dominated by Cryptophyta, nanoflagellates and Cyanobacteria. The freshwater marsh was dominated by Cryptophyta in autumn and winter and by a diverse phytoplankton community in spring. Marine copepods (Calanoida and Harpacticoida) characterized the saltwater metazooplanktonic communities, Cladocerans and Rotifera the freshwater ones. Overall, the planktonic diversity was higher in the freshwater marsh (102 taxa) than in the saltwater marsh (54 taxa).Phytoplankton blooms represented nutrient and CO2 uptake in both marshes and this purification function seemed most efficient in autumn in the saltmarsh. Considerable zooplankton communities represented a potential for nursery. Of the three management actions performed, only periodic water renewals might affect the seasonal dynamics of planktonic communities.

Ecological consequences of genotypic diversity within a foundation plant,Spartina alterniflora, are pervasive but not universal across multiple stress gradients

AbstractPlant genotypic diversity can influence population‐ and community‐level processes, yet we have limited understanding of how these effects vary across environmental gradients that are ubiquitous in nature.We conducted a 2‐year field experiment manipulating plant (Spartina alterniflora) genotypic diversity across a natural stress gradient in tidal elevation, both with and without the addition of nutrients.Spartinadiversity increased stem production, but the magnitude of this effect was reduced at both the most stressful and most benign endpoints of the combined elevation and nutrient gradient, consistent with recent species diversity studies. Complementarity among individuals likely underpins the observed benefit ofSpartinadiversity.Spartinadiversity also affected the associated marsh community, with higher consumer (Littoraria irrorata) abundance in more diverse plots, owing to both greaterSpartinadensity and increased variation inSpartinatraits.Synthesis. The positive effects ofSpartinadiversity on population‐ and community‐level responses under most environmental conditions highlights the ecological importance of plant genotypic diversity for the maintenance of function across the marsh landscape.

Spartina alterniflora invasion differentially alters microbial residues and their contribution to soil organic C in coastal marsh and mangrove wetlands

Coastal wetlands play a critical role in global carbon (C) cycling while they are frequently challenged by exotic plant invasion. Microbial residues are increasingly recognized as the key constituent of stable soil organic C (SOC) but their responses to plant invasion in coastal wetlands remain largely unknown. Here, we investigated the effect of Spartina alterniflora invasion on microbial residues and their contribution to SOC in coastal wetland ecosystems with distinct native species (Phragmites australis (marsh), Kandelia candel or Avicennia marina). S. alterniflora invasion differentially altered microbial residue C accumulation in three coastal wetlands. Overall, the invasion of S. alterniflora significantly increased microbial residue C accumulation (17.8%) in marsh with native P. australis, while it showed negative or minor impacts on mangroves with K. candel and A. marine communities, despite nuanced site-specific differences. The divergent responses of microbial residues could be related to changes in edaphic conditions and plant inputs along with plant invasion process. Invasion of mangrove and marsh communities by S. alterniflora triggered divergent fungal and bacterial residue responses, leading to contrasting fungal to bacterial C ratios in invaded marsh and mangrove wetlands. The proportion of microbial residues in SOC pool was enhanced to some extent, with an increase by 14.4%, 33.0% and 1.9% in P. australis, K. candel and A. marine wetlands, respectively, despite inconsistent variations in total SOC with S. alterniflora invasion. This has an implication for an elevated preservation of microbial residue C relative to the other organic C fractions in the invaded coastal wetlands. These findings highlight the importance of anabolic microbial C sequestration process for the maintenance of wetland soil C, which may impact C cycling and balance in coastal wetland ecosystem subjected to S. alterniflora invasion. Our work provides new insights to capture the properties and mechanisms of microbial control over C sequestration as well as SOC source configuration in coastal wetlands undergoing S. alterniflora invasion.

Factors driving the halophyte rhizosphere bacterial communities in coastal salt marshes.

Root-associated microorganisms promote plant growth and provide protection from stresses. Halophytes are the fundamental components maintaining ecosystem functions of coastal salt marshes; however, it is not clear how their microbiome are structured across large spatial scales. Here, we investigated the rhizosphere bacterial communities of typical coastal halophyte species (Phragmites australis and Suaeda salsa) in temperate and subtropical salt marshes across 1,100 km in eastern China. The sampling sites were located from 30.33 to 40.90°N and 119.24 to 121.79°E across east China. A total of 36 plots were investigated in the Liaohe River Estuary, the Yellow River Estuary, Yancheng, and Hangzhou Bay in August 2020. We collected shoot, root, and rhizosphere soil samples. the number of pakchoi leaves, total fresh and dry weight of the seedlings was counted. The soil properties, plant functional traits, the genome sequencing, and metabolomics assay were detected. The results showed that soil nutrients (total organic carbon, dissolved organic carbon, total nitrogen, soluble sugars, and organic acids) are high in the temperate marsh, while root exudates (measured by metabolite expressions) are significantly higher in the subtropical marsh. We observed higher bacterial alpha diversity, more complex network structure, and more negative connections in the temperate salt marsh, which suggested intense competition among bacterial groups. Variation partitioning analysis showed that climatic, edaphic, and root exudates had the greatest effects on the bacteria in the salt marsh, especially for abundant and moderate subcommunities. Random forest modeling further confirmed this but showed that plant species had a limited effect. Taken together, the results of this study revealed soil properties (chemical properties) and root exudates (metabolites) had the greatest influence on the bacterial community of salt marsh, especially for abundant and moderate taxa. Our results provided novel insights into the biogeography of halophyte microbiome in coastal wetlands and can be beneficial for policymakers in decision-making on the management of coastal wetlands.

Predation cues amplify the effects of parasites on the personality of a keystone grazer.

Parasites can alter species interactions either by modifying infected host behaviour or by influencing behavioural responses in uninfected individuals. Salt marsh ecosystems are characterized by a predator-prey interaction between the keystone grazer, Littoraria irrorata, and its main predator, Callinectes sapidus, both integral players in mediating the productivity of these habitats. Littoraria also acts as the first intermediate host for at least four species of digenetic trematode. Parasite infection has been shown to decrease grazing and climbing in populations of Littoraria, although effects on infected host response to predators have not been investigated. Moreover, how infection might increase or decrease among-individual variation in behaviour (i.e. animal personality) is still unknown. Here we ask how trematode infection affects the expression of boldness in the anti-predator responses of L. irrorata in both the absence and presence of a predator cue. We find that individual boldness varies substantially, and repeatability tends to increase as the number of stressors increases, with infected individuals exposed to a predator cue showing the strongest expression of behavioural types. Parasitism amplifies this effect, although the parasite itself does not appear to directly induce behavioural changes: infected snails show no evidence of decreased climbing or differences in refuge use as compared to their uninfected counterparts. Infection might therefore drive the expression of condition-dependent personality differences evident only under high-risk conditions. Group infection status strongly influenced behavioural reaction norms: uninfected individuals grouped with an infected snail were more responsive to predation risk, exhibiting increased climbing behaviour and spending less time in the water. Here parasites are influencing personality indirectly by inducing avoidance behaviours in healthy individuals, although only in high-risk environments. The potential for exposure to parasites and predators fluctuates greatly across marsh ecosystems. Given the ecological importance of this predator-prey relationship, trematode infection can act as an important, although indirect, determinant of overall salt marsh community structure, health and function.

Seasonality and assembly of soil microbial communities in coastal salt marshes invaded by a perennial grass

Plant invasion profoundly changes the microbial-driven processes in the ecosystem; however, the seasonality of soil microbial communities and their assembly under plant invasion is poorly understood. In this study, coastal salt marshes with native Suaeda salsa (L.) Pall. and exotic Spartina alterniflora Loisel. in the Yellow River Estuary, North China, were selected, and soil bacterial and fungal communities and their seasonal variance were characterized by metabarcoding sequencing of the 16S rRNA gene and ITS2 regions, respectively. The importance of deterministic and stochastic processes in shaping bacterial and fungal seasonal assembly was explored by the null model. Results showed that soil microbes exhibited the lowest diversities in spring, while their diversity significantly improved in summer and autumn with the increase in organic carbon and nitrogen content in soils. Strong seasonal variances in microbial communities were observed, but plant invasion reduced the seasonal variation strength of soil bacteria. For the microbial assembly, the seasonal variability of soil bacterial community was mainly controlled by homogeneous selection, whereas soil fungal community was dominantly structured by stochastic processes. Among the selected variables, soil pH was the key abiotic factor driving the seasonal changes in bacteria and fungi. The microbial function annotation derived from taxonomy-based inference suggested that carbon metabolism was relatively stronger in spring, but nitrogen and sulfur metabolism increased evidently in summer and autumn, and the proportion of saprophytic fungi increased substantially after plant invasion. The seasonal turnover of bacterial and fungal groups were tightly associated with the seasonal variation in soil carbon and nitrogen contents. Collectively, these findings reveal the strong seasonal variability of different soil microbial constituents in plant-invaded coastal salt marshes and suggest the linkage between microbial community assembly and microbial-mediated functions in the context of plant invasions.

Documenting the impacts of increasing salinity in freshwater and coastal ecosystems: Introduction to the special issue

Documenting the impacts of increasing salinity in freshwater and coastal ecosystems: Introduction to the special issue

Spatiotemporal evolution and assembly processes of ammonia-oxidizing prokaryotic communities in 1 000-year-old coastal reclaimed soils

Coastal marshes are transitional areas between terrestrial and aquatic ecosystems. They are sensitive to climate change and anthropogenic activities. In recent decades, the reclamation of coastal marshes has greatly increased, and its effects on microbial communities in coastal marshes have been studied with great interest. Most of these studies have explained the short-term spatiotemporal variation in soil microbial community dynamics. However, the impact of reclamation on the community composition and assembly processes of functional microbes (e.g., ammonia-oxidizing prokaryotes) is often ignored. In this study, using quantitative polymerase chain reaction and the Ion S5™ XL sequencing platform, we investigated the spatiotemporal dynamics, assembly processes, and diversity patterns of ammonia-oxidizing prokaryotes in 1 000-year-old reclaimed coastal salt marshes. The taxonomic and phylogenetic diversity and composition of ammonia oxidizers showed apparent spatiotemporal variations with soil reclamation. Phylogenetic null modelling-based analysis showed that across all sites, the archaeal ammonia-oxidizing community was assembled by a deterministic process (84.71%), and deterministic processes were also dominant (55.2%) for ammonia-oxidizing bacterial communities except for communities at 60 years of reclamation. The assembly process and nitrification activity in reclaimed soils were positively correlated. The abundance of the amoA gene and changes in ammonia-oxidizing archaeal and bacterial diversities significantly affected the nitrification activity in reclaimed soils. These findings suggest that long-term coastal salt marsh reclamation affects nitrification by modulating the activities of ammonia-oxidizing microorganisms and regulating their community structures and assembly processes. These results provide a better understanding of the effects of long-term land reclamation on soil nitrogen-cycling microbial communities.

MEADOW VEGETATION OF THE SEIM RIVER VALLEY WITHIN THE TERRITORY OF THE BURYNA URBAN TERRITORIAL COMMUNITY, KONOTOP DISTRICT, SUMY REGION

As a result of human economic activity, most of the natural habitats of the Seim River valley within the territory of the Buryn city territorial community of Konotop district, Sumy region, have been destroyed. In this regard, there was a need to study the current state of meadow vegetation in this region. Part of the channel and the left bank of the Seim River is located on the territory of Buryn town community, which is characterized by a developed floodplain with meadow and marsh communities, oxbows, and floodplain terraces. During the research conducted in 2007–2022, it was found that meadow vegetation communities were completely destroyed in large areas, and the remaining ones underwent significant changes in the direction of impoverishment of population, species and coenotic biodiversity. It was found that the meadow vegetation of the Seim River valley within the territory of the Buryn city territorial community is represented by the following classes of formations: true, steppe, marshy and peaty meadows. It was found that the largest areas in the research area are occupied by real meadows and their composition includes the formations – Festuceta pratensis, Alopecureta pratensis, Calamagrostideta epigeios, Agrostideta albae, Festuceta rubrae, Phleeta pratensis, Anthoxantete odorati and Poeta pratensis. Steppe meadows are found in the middle section of the floodplain and are represented by two formations – Agrostideta syreistschikovii and Poeta angustifoliae. On the lower areas of the relief, small marshy meadows are not often found and are mostly represented by groups of formations – Glicerieta maximae, Cariceta acutae, Agrostideta stoloniferae. Peat meadows are represented by only one formation Deschampsieta caespitosae. 4 species of the plants brought to the Red Book of Ukraine and 3 – in the Red List of Plant Species, which are regionally rare, uncommon and disappearing and subject to special protection in the Sumy region.

Detritivores and exogenous nitrogen influence litter microbial communities in coastal salt marshes

Saprotrophic fungal communities and animal detritivores are known to regulate litter decomposition, yet their interaction has seldom been examined in coastal salt marshes. Such studies are important because salt marshes have some of the highest carbon storage rates of any ecosystem, and litter plays an important role in carbon cycling. Furthermore, it is currently unknown how species loss and nitrogen (N) pollution will impact the detritivore-fungi or detritivore-algae interactions that occur on litter. To test for changes in the microbial community of decaying Spartina alterniflora Loisel litter, we factorially altered the N concentrations of sediment surrounding the litter as well as the densities of Melampus bidentatus Say, 1822, an abundant but declining detritivorous snail that increases fungal abundance and litter decomposition rates. In each of 36 experimental plots, we analyzed the fungal and algal community composition of litter bundles (collected after 50 and 100 d, respectively) along with detritivore densities, plant traits, sediment and litter N, sediment chemistry, and microclimate. Notably, the densities of snails and isopods were associated with changes in the evenness and relative abundances of fungi in the litter, while amphipods influenced both fungal and algal communities. N additions further altered fungal community structure and increased the dominant saprotroph Natantispora retorquens at both timepoints. In sum, our novel field study revealed that N pollution and the loss of key detritivores, both of which are expected to increase in the future, will likely impact salt marsh fungi. Therefore, global change may impact the animal-microbial dynamics that influence above-ground carbon cycling.