Exploring Multiple Aspects of Taxonomic and Functional Diversity in Microphytobenthic Communities : Effects of Environmental Gradients and Temporal Changes

Biodiversity has traditionally been quantified using taxonomic information but the importance of also considering its functional characteristics has recently gained an increasing attention among microorganisms. However, studies exploring multiple aspects of taxonomic and functional diversity and their temporal variations are scarce for diatoms, which is one of the most important microbial groups in aquatic ecosystems. Here, our aim was to examine the taxonomic and functional alpha and beta diversities of diatoms in a coastal rock pool system characterized by a naturally high environmental heterogeneity. We also investigated the temporal differences in the diversity patterns and drivers. The relationship between the species richness and functional dispersion was temporally coherent, such that species-poor communities tended to be functionally clustered. The trend between the species richness and taxonomic uniqueness of community composition was temporally inconsistent, changing from negative to non-significant over time. Conductivity or distance to the sea or both were key determinants of species richness, functional dispersion, and uniqueness of community composition. The increase of community dissimilarity with an increasing environmental distance was stronger for the taxonomic than the functional composition. Our results suggest that even minor decreases in the species richness may result in a lowered functional diversity and decreased ecosystem functioning. Species-poor ecosystems may, however, have unique species compositions and high contributions to regional biodiversity. Despite changing the species compositions along the environmental gradients, communities may remain to have a high functional similarity and robustness in the face of environmental changes. Our results highlight the advantage of considering multiple biodiversity metrics and incorporating a temporal component for a deeper understanding of the effects of environmental changes on microbial biodiversity.Peer reviewe

Threshold effects of climate change on benthic diatom communities: Evaluating impacts of salinity and wind disturbance on functional traits and benthic biomass

The responses of biotic communities and ecosystems to climate change may be abrupt and non-linear. Thus, resolving ecological threshold mechanisms is crucial for understanding the consequences of climate change and for improving environmental management. Here, we present a study on the threshold responses of benthic diatom communities that are an important component of all aquatic environments and strongly contribute to global primary production. We reach beyond the taxonomic perspective by focusing on the diversity and functions of diatom communities and benthic biomass along gradients of salinity and wind disturbance, whose climate-change-induced changes have been predicted to strongly affect biotic communities in the marine and brackish systems in the future. To improve the generality of our results, we examine three self-collected datasets from different spatial scales (6-830 km) and ecosystem types. We collected samples from rock pools or from littoral stones and studied taxonomic thresholds using Threshold Indicator Taxa Analysis (TITAN2). We investigated threshold responses of community diversity, community functions, and benthic biomass using t-tests and regression analyses. Our results indicated that decreasing salinity may result in increasing diver-sity but decreasing biomass of brackish communities, while the effects of increasing wind disturbance were contradictory among spatial scales. Benthic biomass correlated with the taxonomic and functional diversity, as well as with the body size distribution of communities, highlighting the importance of considering community functions and organismal size when predicting ecosystem functions. The most pronounced effects of decreasing salinity and increasing wind distur-bance on community functions were changes in the abundance of low-profile diatom species, which, due to the high resilience of low-profile diatoms, may lead to changes in ecosystem functioning and resilience. To conclude, decreasing salinity and increasing wind disturbance may lead to threshold responses of biotic communities, and these changes may have profound effects on ecosystem functioning along marine coastal areas.Peer reviewe

Multi-scale drivers of microbial biodiversity across small water bodies in northern regions

The patterns and drivers of microbial biodiversity remain less described and understood than those of larger organisms. Considerable knowledge gaps regarding microorganisms remain especially among small water bodies, which contribute significantly to biodiversity across northern landscapes. The main aims of this thesis were (1) to investigate microbial biodiversity patterns and multi-scale drivers along elevational gradients in subarctic streams and ponds; (2) to explore the effects of species niche characteristics and traits on elevational distributions of pond diatoms; (3) to test for the theory of island biogeography and to identify the factors affecting diatom biodiversity in boreal springs; and (4) to investigate the factors shaping diatom biodiversity along a land-use intensity gradient across boreal streams. To achieve these aims, small streams, ponds, and springs in the boreal and subarctic regions were sampled for microorganisms, and a variety of explanatory variables representing local environmental conditions, catchment properties and climatic and spatial factors were measured or derived from existing databases. The studied microbial groups comprised diatoms, cyanobacteria, and non-cyanobacteria (i.e., bacteria other than cyanobacteria). To examine the relationships between microbial biodiversity and explanatory variables, advanced statistical methods were used. The results showed that in the subarctic streams, diatom species richness or range size exhibited no consistent elevational patterns, whereas community similarity decreased primarily with elevational distance. Diatom communities among the streams were shaped by local-scale variables, such as water depth, and regional drivers, including dispersal and geographical factors. In the subarctic ponds, the richness–elevation relationship was unimodal for diatoms and cyanobacteria, whereas non-cyanobacteria richness declined with increasing elevation. Ponds at both ends of the elevational gradient harboured taxonomically unique microbial communities. The observed patterns were driven by hierarchically structured factors. The variation in species richness and uniqueness of diatom and cyanobacteria communities were best explained by local-scale variables, whereas non-cyanobacteria were also influenced by terrestrial productivity and elevation. Pond diatom distributions were also affected by species niche characteristics and traits: small size and strong acid tolerance were associated with a wider elevational distribution. At the community level, acidic ponds harboured functionally clustered communities. For spring diatoms, no species–area or species–isolation relationships were found; instead, local environmental variables and catchment characteristics were most strongly associated with species richness and community composition. At the relatively small spatial scale studied, diatom biodiversity was apparently not constrained by dispersal-related factors. Along the land-use intensity gradient, changes in stream diatom communities were evident. More intensive land use resulted in decreasing species richness and community compositions comprising more pollution-tolerant species. The variation in diatom richness and community composition was influenced by multiple local-scale factors, which in turn were controlled by catchment properties. In conclusion, this thesis expands current knowledge of microbial biodiversity across small water bodies in the northern regions. Microbial biodiversity in such systems is shaped by multiple factors prevailing at hierarchical spatial scales, the relative importance of which depends on the study system and microbial group. The effects of local-scale factors were emphasised throughout, yet catchment characteristics and spatial variables may also be important. For a deeper understanding of the factors underlying microbial biodiversity, considering multiple inherently different ecosystem types and organism groups is essential.Mikrobien esiintymisessä havaittavia säännönmukaisuuksia ja niitä sääteleviä tekijöitä on tutkittu vähän verrattuna suurempiin eliöihin. Tietämys pieneliöiden esiintymisestä on puutteellista etenkin pienvesissä, jotka lisäävät merkittävästi pohjoisen luonnon monimuotoisuutta. Tämän väitöskirjan tavoitteena on tutkia mikrobien biodiversiteetin säännönmukaisuuksia ja niihin vaikuttavia tekijöitä subarktisissa puroissa ja lammissa sekä boreaalisissa lähteissä ja virtavesissä. Tutkimuksen aineisto koostui erilaisista pienvesistä kerätyistä mikrobinäytteistä ja paikallista ympäristöä, valuma-alueita sekä spatiaalisia ja ilmastotekijöitä kuvaavasta tiedosta. Tutkittuihin mikrobiryhmiin lukeutuivat piilevät, syanobakteerit, ja muut bakteerit kuin syanobakteerit. Muuttujien välisiä suhteita tutkittiin moderneilla tilastollisilla menetelmillä. Subarktisissa pienvesissä mikrobien biodiversiteettiä tutkittiin erityisesti suhteessa korkeusgradienttiin. Tulokset osoittivat, että puroissa esiintyvien piilevien lajirunsaus tai esiintymisalueiden koko ei vaihdellut korkeusgradientin mukaisesti, mutta lajiston samankaltaisuus väheni paikkojen välisen korkeuseron kasvaessa. Purojen piileväyhteisöihin vaikuttivat sekä paikalliset tekijät, kuten veden syvyys, että alueelliset tekijät, kuten leviäminen. Lammissa esiintyvien piilevien ja syanobakteereiden lajirunsaus oli korkeimmillaan korkeusgradientin puolivälissä, kun taas muiden bakteereiden lajirunsaus väheni korkeuden kasvaessa. Lajistoltaan ainutlaatuisia mikrobiyhteisöjä esiintyi korkeusgradientin molemmissa päissä. Lampien mikrobiyhteisöihin vaikuttivat paikalliset ympäristötekijät, lampea ympäröivän maaekosysteemin tuottavuus ja lammen sijainnin korkeus. Piilevien esiintymiseen vaikuttivat myös lajien ekolokeroiden ominaisuudet ja lajien piirteet: pienet ja happamuutta sietävät lajit omasivat laajimmat esiintymisalueet korkeusgradientin suhteen. Veden happamuus vaikutti myös yhteisötasolla vähentäen funktionaalista diversiteettiä. Lähteissä esiintyvien piilevien lajirunsaus ei ollut riippuvainen ekosysteemin koosta tai eristyneisyydestä paikallisen ympäristön ja valuma-aluetekijöiden säädellessä lajirunsautta ja yhteisökoostumusta. Maankäytön intensiteetti ja vedenlaatu vaikuttivat selvästi virtavesien piileväyhteisöihin; intensiivinen maankäyttö laski lajirunsautta ja lisäsi kuormitusta sietävien lajien osuutta yhteisöissä. Tämä työ lisää tietämystä pohjoisissa pienvesissä esiintyvien mikrobien biodiversiteetistä. Tutkimus osoittaa, että pienvesien mikrobiyhteisöihin vaikuttavat useat eri mittakaavoilla toimivat tekijät. Eri pienvesityyppien ja mikrobiryhmien tutkiminen toi esiin eroja vaikuttavien tekijöiden keskinäisessä tärkeydessä, korostaen useiden erilaisten ekosysteemityyppien ja organismiryhmien samanaikaisen tarkastelun hyödyllisyyttä tutkittaessa luonnon monimuotoisuutta sääteleviä tekijöitä

Piilevien lajirunsauden ja yhteisökoostumuksen vaihtelu boreaalisissa lähteissä

Multiple factors operating at several different scales affect formation of local communities. Local communities are hierarchically structured being controlled by historical, dispersal related and local present day abiotic and biotic factors. In isolated island-like habitats species richness is also often affected by ecosystem size and isolation. These patterns in species richness and community composition usually examined for macroorganisms have been increasingly studied recently also for microorganisms. This thesis examines the variation in diatom species richness and community composition in 50 boreal springs. Specifically, I investigate whether there is a relationship between species richness and spring area and isolation. In addition, the aim is to disentangle which are the most essential local environmental factors, drainage basin variables and spatial factors that account for variation in species richness and community composition. Compared to other inland waters springs have been much less studied. Springs provide exceptionally stable yet isolated growing conditions, being threatened by changes in land use, however. Material comprised water quality data, data on local physical environment, drainage basin variables derived from CORINE Land Cover 2006, and spring coordinates as spatial variables. Diatom samples were collected simultaneously with water sampling in years 2011-2012. Statistical methods used were linear regression analysis and various multivariate methods such as generalized linear models (GLM), redundancy analysis, analysis of similarities and variation partitioning. There were non-significant relationships between species richness and spring area and isolation. According to GLM-model, the variation in species richness was related with several local proximate resource and stress factors such as total phosphorus concentration, pH and color. Based on redundancy analysis, the key variables affecting variation in community composition were pH, conductivity, temperature and color. Purely local environmental factors accounted for most of the explainable variation in both species richness (42,6 %) and community composition (21,1 %) in variation partitioning. Drainage basin variables explained a small amount of variation, whereas geographical location alone did not show any pure effect on species richness or composition. The results of the analysis of similarities did not show any significant differences in community compositions between ecoregions. These results suggest that local environmental variables are the most influential factors controlling diatom species richness and community composition in springs whereas drainage basin variables and spatial factors are much less important. Species richness is also not affected by spring size or isolation. At this study scale, diatoms seem thus to be more or less freely dispersed among the springs. Regardless of location species thrive in springs where their habitat requirements are fulfilled. Thus, species are filtered into local communities from regional species pool mainly via local environmental factors.Paikallisten eliöyhteisöjen muodostumiseen vaikuttavat useat erilaisilla mittakaavatasoilla toimivat tekijät. Eliöyhteisöt rakentuvat hierarkkisesti historiallisten, leviämiseen liittyvien ja nykyisten paikallisten abioottisten ja bioottisten tekijöiden ohjaamina. Eristyneissä elinympäristöissä myös ekosysteemin koolla ja eristyneisyydellä on usein merkitystä lajirunsaudelle. Edellä mainittujen yleensä makro-organismeilla tutkittujen lajirunsauden ja yhteisökoostumuksen säännönmukaisuuksien tutkiminen on lisääntynyt viime aikoina myös mikro-organismeilla. Tässä tutkielmassa tarkastellaan piilevien lajirunsauden ja yhteisökoostumuksen vaihtelua 50 boreaalisessa lähteessä. Tutkimuksessa selvitän, onko lajirunsauden ja lähteen pinta-alan ja eristyneisyyden välillä riippuvuutta. Lisäksi tavoitteena on selvittää keskeiset lajirunsauden ja yhteisökoostumuksen vaihteluun vaikuttavat paikalliset ympäristötekijät, valuma-aluemuuttujat ja spatiaaliset tekijät. Lähteet ovat muihin sisävesiin verrattuna vähän tutkittuja ympäristöjä. Ne tarjoavat poikkeuksellisen vakaat, mutta eristyneet, kasvuolosuhteet. Lähteiden tilaa uhkaavat kuitenkin maankäytön muutokset. Tutkimuksen aineistona käytettiin vedenlaatutietoa, tietoa paikallisesta fysikaalisesta ympäristöstä, CORINE Land Cover 2006 aineistosta johdettuja valuma-aluemuuttujia ja lähteiden koordinaatteja spatiaalisina muuttujina. Piilevänäytteet kerättiin vesinäytteiden oton yhteydessä vuosina 2011-2012. Tilastollisina menetelminä käytettiin lineaarista regressioanalyysiä ja erilaisia monimuuttujamenetelmiä, joita olivat yleistetyt lineaariset mallit, redundanssianalyysi, similariteettianalyysi ja hajonnan ositus. Lähteen koolla tai eristyneisyydellä ei ollut tilastollisesti merkitsevää vaikutusta lajirunsauteen. GLM-mallin mukaan lajirunsauden vaihtelua säätelivät useat paikalliset proksimaattiset resurssi- ja stressitekijät, kuten kokonaisfosforipitoisuus, pH ja väri. Redundanssianalyysin mukaan tärkeimpiä yhteisökoostumuksen vaihteluun vaikuttavia tekijöitä olivat pH, sähkönjohtokyky, lämpötila ja väri. Hajonnan osituksen mukaan puhtaasti paikalliset ympäristötekijät selittivät eniten sekä lajirunsauden (42,6 %) että yhteisökoostumuksen (21,1 %) vaihtelusta. Valuma-aluemuuttujat selittivät pienen osan vaihtelusta, kun taas puhtaasti maantieteellisellä sijainnilla ei ollut vaikutusta lajirunsauteen tai yhteisökoostumukseen. Similariteettianalyysin mukaan yhteisökoostumuksissa ei ollut merkitseviä eroja boreaalisten vyöhykkeiden välillä. Näiden tulosten pohjalta voidaan sanoa, että paikalliset ympäristötekijät ovat keskeisiä piilevien lajirunsauden ja yhteisökoostumuksen vaihtelua lähteissä sääteleviä muuttujia valuma-aluemuuttujien ja spatiaalisten tekijöiden ollessa vähemmän tärkeitä. Lähteen koolla tai eristyneisyydellä ei ole myöskään vaikutusta lajirunsauteen. Tällä tutkimusmittakaavalla piilevien leviäminen vaikuttaa olevan melko rajatonta, sillä lajit menestyvät sijainnista riippumatta lähteissä, joissa niiden elinympäristövaatimukset täyttyvät. Lajit valikoituvat lähteiseen alueellisesta lajistosta lähinnä paikallisten ympäristötekijöiden suodattamina

Studying biodiversity-ecosystem function relationships in experimental microcosms among islands

Ecological studies on islands have provided fundamental insights into the mechanisms underlying biodiversity of larger organisms, but we know little about the factors affecting island microbial biodiversity and ecosystem function. We conducted a field experiment on five Baltic Sea islands where we placed aquatic microcosms with different levels of salinity mimicking environmental stress and allowed diatoms to colonize the microcosms via the air. Using structural equation models (SEM), we investigated the interconnections among environmental and dispersal-related factors, diatom biodiversity, and ecosystem productivity (represented by chlorophyll a concentration). We also tested whether the body size structure of the community influences productivity together with biodiversity. In SEMs, we found no relationship between species richness or evenness and productivity. However, productivity increased with increasing mean body size of species in the communities. The effects of environmental stress on both biodiversity and ecosystem productivity were highlighted as species richness and evenness declined, whereas productivity increased at the highest salinity levels. In addition to salinity, wind exposure affected both biodiversity metrics and productivity. This study provides new insights into microbial community assembly in a field experimental setting and the relationship between biodiversity and ecosystem function. Our results indicate that salinity presents a strong abiotic filter, leading to communities that may be species poor, yet comprise salinity-tolerant and relatively productive species at high salinity. Our findings also emphasize the importance of mean community body size in mediating the effects of environmental conditions on productivity and suggest that this trait should be considered more broadly in biodiversity-ecosystem function studies.Peer reviewe

High diatom species turnover in a Baltic Sea rock pool metacommunity

Different metacommunity perspectives have been developed to describe the relationship between environmental and spatial factors and their relative roles for local communities. However, only little is known about temporal variation in metacommunities and their underlying drivers. We examined temporal variation in the relative roles of environmental and spatial factors for diatom community composition among brackish-watered rock pools on the Baltic Sea coast over a 3-month period. We used a combination of direct ordination, variation partition, and Mantel tests to investigate the metacommunity patterns. The studied communities housed a mixture of freshwater, brackish, and marine species, with a decreasing share of salinity tolerant species along both temporal and spatial gradients. The community composition was explained by both environmental and spatial variables (especially conductivity and distance from the sea) in each month; the joint effect of these factors was consistently larger than the pure effects of either variable group. Community similarity was related to both environmental and spatial distance between the pools even when the other variable group was controlled for. The relative influence of environmental factors increased with time, accounting for the largest share of the variation in species composition and distance decay of similarity in July. Metacommunity organization in the studied rock pools was probably largely explained by a combination of species sorting and mass effect given the small spatial study scale. The found strong distance decay of community similarity indicates spatially highly heterogeneous diatom communities mainly driven by temporally varying conductivity gradient at the marine-freshwater transition zone.Peer reviewe

Factors influencing the biodiversity of three microbial groups within and among islands of the Baltic Sea

Islands provide ideal model systems to examine the factors influencing biodiversity, yet knowledge of microbial biodiversity on islands remains scarce. We collected a dataset from 101 rock pools along a freshwater to brackish water transition on islands of the Baltic Sea and investigated the patterns and drivers of community composition and species richness of diatoms, cyanobacteria and non-cyanobacteria bacteria among islands. We also examined whether environmental heterogeneity increased beta diversity and species richness within islands. Among islands, the patterns in community composition were concordant among the microbial groups, with distinct changes along the freshwater-brackish gradient. The patterns in species richness were context-dependent for each microbial group. In general, richness patterns were most strongly associated with nutrient concentrations or the distances to potential sources of immigrants, whereas no positive relationships between ecosystem size and richness were found. Within islands, environmental heterogeneity was positively correlated with the beta diversity of each microbial group, but not species richness. Our findings provide novel insights into the factors influencing microbial biodiversity. The results suggest that island microbial biodiversity patterns are influenced by species sorting and dispersal-related mechanisms and highlight the importance of environmental heterogeneity for beta diversity.Peer reviewe

Local and geographical factors jointly drive elevational patterns in three microbial groups across subarctic ponds

Aim: Elevational biodiversity patterns are understudied in high-latitude aquatic systems, even though these systems are important for detecting very early impacts of climatic changes on Earth. The aim of this study was to examine the elevational trends in species richness and local contribution to beta diversity (LCBD) of three biofilm microbial groups in freshwater ponds and to identify the key mechanisms underlying these patterns. Location: One hundred and forty-six ponds in subarctic Finland and Norway distributed across the tree line along an elevational gradient of 10-1,038 m a.s.l., spanning from forested landscape to barren boulder fields. Time period: July-August 2015. Major taxa studied: Diatoms, cyanobacteria and non-cyanobacteria. Methods: Generalized linear models were used to identify the most important pond variables explaining richness and LCBD. Structural equation models were used to explore the direct and indirect effects of multiscale drivers on richness and LCBD. Results: Diatom and cyanobacteria richness showed unimodal elevational patterns, whereas non-cyanobacteria richness decreased with increasing elevation. The LCBD-elevation relationship was U-shaped for all three microbial groups. Diatom and cyanobacteria richness and LCBD were best explained by local pond variables, especially by pH. Non-cyanobacteria richness and LCBD were related to pond variables, elevation as a proxy for climatic conditions, and normalized difference vegetation index as a proxy for terrestrial productivity. Main conclusions: Aquatic autotrophs were primarily controlled by environmental filtering, whereas heterotrophic bacteria were also affected by terrestrial productivity and elevation. All studied aspects of microbial diversity were directly or indirectly linked to elevation; therefore, climatic changes may greatly alter aquatic microbial assemblages.Peer reviewe

Stream diatom community assembly processes in islands and continents: a global perspective

[EN] Understanding the roles of deterministic and stochastic processes in community assembly is essential for gaining insights into the biogeographical patterns of biodiversity. However, the way community assembly processes operate is still not fully understood, especially in oceanic islands. In this study, we examine the importance of assembly processes in shaping diatom communities in islands and continents, while also investigating the influence of climate and local water chemistry variables on species distributions. Location Global. Taxon Stream benthic diatoms. Methods We used diatom datasets from five continents and 19 islands and applied beta diversity analyses with a null model approach and hierarchical joint species distribution modelling. To facilitate comparisons with continents, we used continental area equivalents (CAEs), which represent continental subsets with comparable areas and the same number of study sites as their corresponding islands counterparts. Results We found that homogeneous selection (i.e., communities being more similar than the random expectation) was the dominant assembly process within islands whereas stochastic processes tended to be more important within continents. In addition, assembly processes were influenced by study scale and island isolation. Climatic variables showed a greater influence on species distribution than local factors. However, in islands, local environmental variables had a greater impact on the distributions of unique taxa as opposed to non-unique taxa. Main Conclusions We observed that the assembly processes of diatom communities were complex and influenced by a combination of deterministic and stochastic forces, which varied across spatial scales. In islands, there was no universal pattern of assembly processes, given that their influence depends on abiotic conditions such as area, isolation, and environmental heterogeneity. In addition, the sensitivity of species occurring uniquely in islands to local environmental variables suggests that they are perhaps less vulnerable to climatic changes but may be more influenced by changes in local physicochemistrySIFor financial support, the authors thank the Academy of Finland (grant nr. 346812 to JS); the Institut Francais de Finlande; the Embassy of France to Finland; the French Ministry of Education and Higher Education; Finnish Society of Sciences and Letters. J.J. Wang was further supported by the National Natural Science Foundation of China (91851117, 41871048), CAS Key Research Program of Frontier Sciences (QYZDB-SSW-DQC043), and The National Key Research and Development Program of China (2019YFA0607100