Cross-Site Soil Microbial Communities under Tillage Regimes: Fungistasis and Microbial Biomarkers

The exploitation of soil ecosystem services by agricultural management strategies requires knowledge of microbial communities in different management regimes. Crop cover by no-till management protects the soil surface, reducing the risk of erosion and nutrient leaching, but might increase straw residue-borne and soilborne plant-pathogenic fungi. A cross-site study of soil microbial communities and Fusarium fungistasis was conducted on six long-term agricultural fields with no-till and moldboard-plowed treatments. Microbial communities were studied at the topsoil surface (0 to 5 cm) and bottom (10 to 20 cm) by general bacterial and actinobacterial terminal restriction fragment length polymorphism (T-RFLP) and phospholipid fatty acid (PLFA) analyses. Fusarium culmorum soil fungistasis describing soil receptivity to plant-pathogenic fungi was explored by using the surface layer method. Soil depth had a significant impact on general bacterial as well as actinobacterial communities and PLFA profiles in no-till treatment, with a clear spatial distinction of communities (P < 0.05), whereas the depth-related separation of microbial communities was not observed in plowed fields. The fungal biomass was higher in no-till surface soil than in plowed soil (P < 0.07). Soil total microbial biomass and fungal biomass correlated with fungistasis (P < 0.02 for the sum of PLFAs; P < 0.001 for PLFA 18:2ω6). Our cross-site study demonstrated that agricultural management strategies can have a major impact on soil microbial community structures, indicating that it is possible to influence the soil processes with management decisions. The interactions between plant-pathogenic fungi and soil microbial communities are multifaceted, and a high level of fungistasis could be linked to the high microbial biomass in soil but not to the specific management strategy.     

Submerged versus air-exposed intertidal macrophyte productivity: from physiological to community-level assessments

The photosynthetic productivity of the intertidal communities dominated by the seagrass Zostera noltii and the cordgrass Spartina maritima was assessed in two contrasting situations during a tidal cycle, i.e., air exposure and water immersion. Two complementary methods were used: infra red gas analysis of CO₂ flux measurements in whole communities and chlorophyll a fluorescence measurements of individual plants photosynthetic activity. Higher photosynthetic rates of Z. noltii in air were observed both at the individual plants response level determined by chlorophyll fluorescence and at the community level measured as gas exchange (CO₂ uptake). S. maritima plants consistently showed low photosynthetic response when immersed. Gross community production (GCP) measured as carbon dioxide uptake was always higher in air than in water for both communities. When immersed, the GCP of both communities was similar. However, when exposed to the air, the GCP of the S. maritima community was higher than the one of Z. noltii's. The key factor in CO₂ assimilation by air-exposed Z. noltii was the retention of water in sediment microdepressions. During low tide, depressions in the sediment retain a considerable amount of water, enough to maintain leaf hydration. In these conditions, rapid air-water CO₂ diffusion occurs, making it readily available to plants. The community gas exchange measurements compared well with the fluorescence indications. Both Z. noltii and S. maritima were shown to be responsible for the overall pattern of photosynthetic carbon fixation within their respective communities, both during submersion and emersion periods. The short-term incubations method described in this report proved to be a valuable tool for field measurements of intertidal lagoon productivity. It provides fast and precise values of carbon dioxide fixation, both in submerged and air-exposed communities.     

Yeast Communities of Diverse Drosophila Species: Comparison of Two Symbiont Groups in the Same Hosts

The combination of ecological diversity with genetic and experimental tractability makes Drosophila a powerful model for the study of animal-associated microbial communities. Despite the known importance of yeasts in Drosophila physiology, behavior, and fitness, most recent work has focused on Drosophila-bacterial interactions. In order to get a more complete understanding of the Drosophila microbiome, we characterized the yeast communities associated with different Drosophila species collected around the world. We focused on the phylum Ascomycota because it constitutes the vast majority of the Drosophila-associated yeasts. Our sampling strategy allowed us to compare the distribution and structure of the yeast and bacterial communities in the same host populations. We show that yeast communities are dominated by a small number of abundant taxa, that the same yeast lineages are associated with different host species and populations, and that host diet has a greater effect than host species on yeast community composition. These patterns closely parallel those observed in Drosophila bacterial communities. However, we do not detect a significant correlation between the yeast and bacterial communities of the same host populations. Comparative analysis of different symbiont groups provides a more comprehensive picture of host-microbe interactions. Future work on the role of symbiont communities in animal physiology, ecological adaptation, and evolution would benefit from a similarly holistic approach.     

Thermophilous oak forests in the Czech Republic: Syntaxonomical revision of theQuercetalia pubescenti-petraeae

Using the Braun-Blanquet approach, a syntaxonomical revision of the order ofQuercetalia pubescenti-petraeae, based on the synthesis of 634 relevés, distinguished three alliances of the thermophilous oak forests in the Czech Republic: (1)Quercion pubescenti-petraeae (3 communities:Pruno mahaleb-Quercetum pubescentis, Lathyro versicoloris-Quercetum pubescentis, Corno-Quercetum), which includes peri-alpine and peri-Carpathian oak forests on calcareous bedrock, (2)Aceri tatarici-Quercion (2 communities:Quercetum pubescenti-roboris, Carici fritschii-Quercetum roboris), which comprises Pontic-Pannonian oak forests on loess or sand that occur in southern Moravia only, (3)Quercion petraeae (5 communities:Potentillo albae-Quercetum, Brachypodium pinnatum-Quercus robur community,Sorbo torminalis-Quercetum, Genisto pilosae-Quercetum petraeae, Asplenio cuneifolii-Quercetum petraeae), which includes Central European thermophilous oak forests distributed outside the range ofQuercus pubescens and some other submediterranean species.     

筑坝扩容下高原湿地拉市海植物群落分布格局及其变化

基于遥感与地理信息系统技术、结合实地调查与验证,对高原湿地拉市海筑坝扩容13a来湿地植物群落类型、物种组成、空间分布格局进行研究,对比分析筑坝扩容前后植物群落变化特征。结果表明,拉市海当前分布有水葱 (Scirpus tabernaemontani)、两栖蓼 (Polygonum amphibium) 等2个挺水植物群落,鸭子草 (Potamogeton tepperi)、菱 (Trapa bispinosa)等2个浮叶植物群落,穗状狐尾藻 (Myriophyllum spicatum)、篦齿眼子菜 (Potamogeton pectinatus)、菹草 (Potamogeton crispus)、穿叶眼子草 (Potamogeton perfoliatus)、小叶眼子菜 (Potamogeton pusillns)等5个沉水植物群落,草甸植被分布于湖周。湿地植物物种共计61种,隶属于25科、48属,物种丰富度随沉水→浮叶→挺水→草甸逐渐增加。沉水植物群落分布面积最大(615.08 hm²),其次是草甸(214.60 hm²)、浮叶植物群落(140.01 hm²),挺水植物群落分布面积最小 (9.34 hm²),群落垂直层次随沉水→浮叶→挺水呈复杂化的趋势。筑坝13a来,拉市海植物群落类型从单一的沉水型植物群落发展成为由沉水、浮叶、挺水型组成的、水平空间多样化配置的湿地植被系统,其中穗状狐尾藻、篦齿眼子菜、小眼子菜等植物群落在筑坝蓄水13a后没有发生演替得以保留,而扇叶水毛茛(Butrachium bungei)、马来眼子菜(Potamogeton malaianus)和轮藻(Chara spp.)群落发生演替而消失。研究掌握了筑坝扩容下拉市海湿地植物群落分布格局及其变化特征,为科学评估筑坝蓄水对湿地生态系统的影响提供了基础性数据,同时也为水文改变下高原湿地生态系统的保护、管理以及资源可持续利用提供了一定的理论依据。     

Changes amid constancy: Flower and leaf microbiomes along land use gradients and between bioregions

Microbial communities inhabiting above-ground parts of plants affect their host's development, fitness and function. Although studies on plant-associated microbes are of growing interest, environmental drivers of flower microbiomes in particular are poorly characterized. In this study, we investigated flower and leaf epiphytic bacterial microbiomes of Ranunculus acris and Trifolium pratense using metabarcoding of 16S ribosomal DNA in three German bioregions and along land-use intensity gradients. Our data suggests that the structures of bacterial communities clearly differed between plant species and tissue types. Also, floral bacterial communities of R. acris showed higher variability in comparison to T. pratense. Bacteria usually associated with pollinators were found solely in flower samples, while bacteria usually associated with the rhizosphere were only present in high abundances on leaves. We identified Pseudomonadaceae, Enterobacteriaceae and Sphingomonadaceae as the most abundant taxa on flowers, while Sphingomonadaceae, Methylobacteriaceae and Cytophagaceae dominated bacterial communities on leaves. We found that bacterial communities did not differ between long-distant regions. However, there was a turnover within each bioregion between short-distant locations. High land use intensity caused phylogenetically less diverse and more homogenous bacterial communities with an exception of T. pratense flowers. This was associated with a loss of rare bacterial families. Intensification of mowing affected the bacterial communities associated with leaves of T. pratense and fertilization led to more homogenous flower and leaf communities of R. acris, while grazing had no effects on the bacterial community composition. However, dominant taxa were not affected by land use intensification. Despite that, we identified indicator taxa for regularly disturbed environments in flower microbiomes. In conclusion, our study contributes to the knowledge about microbial community structures of the phyllosphere and extends the understanding of their community dynamics with respect to biogeographical separation and anthropogenic changes of the environment.     

Invasiveness and impact of the non-native shrub Baccharis halimifolia in sea rush marshes: fine-scale stress heterogeneity matters

The invasion of the exotic dioecious shrub Baccharis halimifolia is transforming the estuarine communities of Southern Europe. Large scale gradients of salinity and flooding regime determine B. halimifolia zonations in salt marshes where the subhalophilous sea rush communities are the most affected by invasion. In this study we aim to (1) assess the invasion level and influence of B. halimifolia on native flora and to (2) quantify the performance of the exotic shrub in rush communities across fine-scale salinity and waterlogging gradients. Using floristic data collected in estuaries in Northern Spain we identified 3 sea rush community subtypes: low, medium and high salinity communities. B. halimifolia cover decreased from low to high salinity communities. Native species cover, richness and diversity and herbaceous-subshrub layer cover was significantly lower in invaded rush communities than in uninvaded ones. The reduction of the singular native estuarine species cover and richness was higher in the high and medium salinity community than in the low salinity community. Growth and reproductive traits measured on two consecutive years in invaded rush communities in Urdaibai Biosphere Reserve indicated that increased edaphic stress reduced B. halimifolia individual performance and enhanced attack by natural enemies. Moreover, leaf drop was more responsive to salinity in female than in male individuals. We conclude that fine-scale variations on edaphic stress played an important role in the invasibility of rush communities by affecting the individual performance of B. halimifolia, and might generate sex specific responses. The implications for rush marsh conservation are discussed.     

Replacement of native seagrass with invasive algal detritus: impacts to estuarine sediment communities

Biological invasions modify the quality and supply of detrital subsidies to aquatic and terrestrial ecosystems. Where the invader has very different traits to native species, major changes in associated consumer communities may result, as a consequence of differences in their nutritional value and effects on the sedimentary habitat. We assessed how the replacement of seagrasses with the invasive alga Caulerpa taxifolia in modified Australian estuaries influences invertebrate communities of mudflats that are subsidized by detritus from submerged aquatic vegetation. Two months after experimental enrichment of sediments with high (60?g dry weight per 0.25?m² plot) or low (30?g dry weight) quantities of either non-native C. taxifolia or native Posidonia australis or Zostera capricorni detritus, there were positive effects of detrital addition on invertebrate abundance that occurred irrespective of the resource added. By 4?months after addition, however, detritus from invasive C. taxifolia had produced effects on benthic communities that could not be replicated by detritus from either of the native seagrasses. Plots receiving the high loading of C. taxifolia detritus contained fewer invertebrates than plots of the other treatments, perhaps due to the induction of sediment hypoxia. The pattern, however, reversed at low detrital loading, with the plots receiving 30?g of C. taxifolia containing more invertebrates and more taxa than the other plots, presumably due to the greater resource availability for detritivores. Our results demonstrate that replacement of native seagrass with invasive algal detritus can have large impacts on sediment-dwelling communities.     

cytoNet: Spatiotemporal network analysis of cell communities

We introduce cytoNet, a cloud-based tool to characterize cell populations from microscopy images. cytoNet quantifies spatial topology and functional relationships in cell communities using principles of network science. Capturing multicellular dynamics through graph features, cytoNet also evaluates the effect of cell-cell interactions on individual cell phenotypes. We demonstrate cytoNet’s capabilities in four case studies: 1) characterizing the temporal dynamics of neural progenitor cell communities during neural differentiation, 2) identifying communities of pain-sensing neurons in vivo, 3) capturing the effect of cell community on endothelial cell morphology, and 4) investigating the effect of laminin α4 on perivascular niches in adipose tissue. The analytical framework introduced here can be used to study the dynamics of complex cell communities in a quantitative manner, leading to a deeper understanding of environmental effects on cellular behavior. The versatile, cloud-based format of cytoNet makes the image analysis framework accessible to researchers across domains.     

Community Resilience in Southern Appalachia: A Theoretical Framework and Three Case Studies

A fundamental assumption in nearly all research on social adaptation to environmental change is that there is a concomitant and inverse relationship between human communities’ dependence upon particular natural resources affected by environmental change and those communities or societies’ resilience to disturbances. However, recent theoretical and empirical developments suggest resilience is a dynamic social process determined, in part, by the ability of communities to act collectively and solve common problems. The interactional approach to community is utilized to develop a framework whereby various patterns of social interaction define the process of social resilience. Data come from multiple mixed methods case studies of forest dependent communities within Southern Appalachia. The findings reveal varied processes of social resilience can occur in communities with similar levels of resource dependence; a community’s composition of internal social ties and their cross-scale linkages to external agencies and organizations define these processes.     

Nitrogen-fixing bacteria, arbuscular mycorrhizal fungi, and the productivity and structure of prairie grassland communities

Due to their complementary roles in meeting plant nutritional needs, arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing bacteria (N₂-fixers) may have synergistic effects on plant communities. Using greenhouse microcosms, we tested the effects of AMF, N₂-fixers (symbiotic: rhizobia, and associative: Azospirillum brasilense), and their potential interactions on the productivity, diversity, and species composition of diverse tallgrass prairie communities and on the productivity of Panicum virgatum in monoculture. Our results demonstrate the importance of AMF and N₂-fixers as drivers of plant community structure and function. In the communities, we found a positive effect of AMF on diversity and productivity, but a negative effect of N₂-fixers on productivity. Both AMF and N₂-fixers affected relative abundances of species. AMF shifted the communities from dominance by Elymus canadensis to Sorghastrum nutans, and seven other species increased in abundance with AMF, accounting for the increased diversity. N₂-fixers led to increases in Astragalus canadensis and Desmanthus illinoense, two legumes that likely benefited from the presence of the appropriate rhizobia symbionts. Sorghastrum nutans declined 44?% in the presence of N₂-fixers, with the most likely explanation being increased competition from legumes. Panicum monocultures were more productive with AMF, but showed no response to N₂-fixers, although inference was constrained by low Azospirillum treatment effectivity. We did not find interactions between AMF and N₂-fixers in communities or Panicum monocultures, indicating that short-term effects of these microbial functional groups are additive.     

Benthic development on large-scale engineered reefs: A comparison of communities among breakwaters of different age and natural reefs

Breakwaters represent large-scale engineered artificial reefs that can develop diverse and abundant communities and are likely to play an increasing role in marine ecosystems as human populations grow in coastal urban areas. Information on how these communities develop and if and when these communities begin to resemble those on natural hard-bottom habitat is essential for marine management, but is not well understood. In this study, benthic communities on six breakwaters ranging from 1 to 31 years of age were compared to provide an understanding of patterns of community development on engineered coastal defenses, and these were compared to communities on natural reefs to gain an understanding of how communities develop on artificial structures relative to those in natural habitats. Multivariate analyses indicated that benthic communities on breakwaters became more similar to natural reefs with increasing age, but that communities on even the most mature (31 years) breakwater were distinct from those on natural reefs (ANOSIM p < 0.001). Generally, breakwaters ≤5.5 years had higher abundance of turf algae, sponges, bivalves, and bare pavement, while more mature (≥25 years) breakwaters were dominated by corals. Coral cover on 25 and 31 years old breakwaters (46% and 56%, respectively) was significantly higher than on natural reefs (37%; HSD test p < 0.05 and p < 0.001, respectively). These results indicate that breakwaters develop benthic communities that continue to change over periods exceeding 31 years, and that although they become more similar to communities on natural reefs with increasing age, these communities remain distinct.     

Effects of climate change on parasitic plants: the root hemiparasiticOrobanchaceae

Climate change may affect hemisparasiticOrobanchaceae (ex-Scrophulariaceae) both directly through impacts on hemiparasite physiology and indirectly through impacts on host plants. This dual action suggests particular sensitivity of the parasite to climate change and any associated impacts on hosts and other members of the community. While little research has addressed the responses of parasitic plants to climate change in natural environments, impacts are predicted from controlled environment studies together with a knowledge of the key ecophysiological traits of hemiparasiticOrobanchaceae, in particular ofStriga species, which are important weeds in semi-arid tropical agro-ecosystems, andRhinanthus species, which can be important components of (principally) grassland communities in the northern temperate zone. The main mode of important components of (principally) grassland communities in the northern temperate zone. The main mode of action of both elevated CO₂ and warming will be through changes in photosynthesis and stomatal functioning. Enhanced photosynthesis of the hemiparasite and host will increase parasite carbon gains but may also increase the demand for host mineral nutrients. Mineral nutrition may, therefore, mediate the impacts of climate change on host-parasite associations. The relative insensitivity of hemiparasite stomata to elevated CO₂ suggests that high stomatal conductances may be maintained and thus solute uptake may become limited by soil drying driven by higher rates of evapotranspiration and reduced precipitation. Climate change impacts on host-parasite interactions at the individual level will ultimately affect hemiparasite impacts at the community level. Community impacts will be greatest where climate change considerably favours hemiparasite populations or, conversely, causes them to disappear from communities where they were formerly abundant. Impacts will further be mediated by climate impacts on hosts, and the natural enemies of hosts and parasites alike. Further, the wide host range of many root hemiparasitic plants may facilitate migration of their populations through new communities under a changing climate.     

The ambrosia symbiosis is specific in some species and promiscuous in others: evidence from community pyrosequencing

Symbioses are increasingly seen as dynamic ecosystems with multiple associates and varying fidelity. Symbiont specificity remains elusive in one of the most ecologically successful and economically damaging eukaryotic symbioses: the ambrosia symbiosis of wood-boring beetles and fungi. We used multiplexed pyrosequencing of amplified internal transcribed spacer II (ITS2) ribosomal DNA (rDNA) libraries to document the communities of fungal associates and symbionts inside the mycangia (fungus transfer organ) of three ambrosia beetle species, Xyleborus affinis, Xyleborus ferrugineus and Xylosandrus crassiusculus. We processed 93 beetle samples from 5 locations across Florida, including reference communities. Fungal communities within mycangia included 14–20 fungus species, many more than reported by culture-based studies. We recovered previously known nutritional symbionts as members of the core community. We also detected several other fungal taxa that are equally frequent but whose function is unknown and many other transient species. The composition of fungal assemblages was significantly correlated with beetle species but not with locality. The type of mycangium appears to determine specificity: two Xyleborus with mandibular mycangia had multiple dominant associates with even abundances; Xylosandrus crassiusculus (mesonotal mycangium) communities were dominated by a single symbiont, Ambrosiella sp. Beetle mycangia also carried many fungi from the environment, including plant pathogens and endophytes. The ITS2 marker proved useful for ecological analyses, but the taxonomic resolution was limited to fungal genus or family, particularly in Ophiostomatales, which are under-represented in our amplicons as well as in public databases. This initial analysis of three beetle species suggests that each clade of ambrosia beetles and each mycangium type may support a functionally and taxonomically distinct symbiosis.     

Replacement of estuarine communities by an exotic shrub: distribution and invasion history of Baccharis halimifolia in Europe

Baccharis halimifolia L. (Asteraceae) is a shrub native to North America which is invading estuarine communities in Europe. We report the invasion history and the distribution limits of B. halimifolia in Europe, with particular emphasis on the frequency of its presence in estuarine communities in Spain. B. halimifolia has been cultivated in Europe since the 17th century to present. It was first recorded as naturalized in the Bay of Biscay in 1906, where it forms currently stable and locally abundant populations in almost all the estuaries of Northern Spain and Western France. The ongoing invasion to the west could reach well conserved estuarine communities in Galicia (Spain). B. halimifolia also forms scattered populations in Northern and Southern France, Belgium, Netherlands, United Kingdom and Italy. In these countries it has experienced a rapid expansion during the last years. In Northern Spain, subhalophilous communities dominated by rush (Juncus maritimus) and/or sea couch (Elytrigia atherica), common reed stands (Phragmites australis) and ungrazed wet meadows are the most vulnerable to invasion. The subhalophilous communities are part of natural habitats of community interest according to the habitats directive 92/43/EEC. In some areas of Northern Spain these communities have been totally replaced by monospecific stands of B. halimifolia. In contrast, halophilous communities of the low marsh are resistant to invasion, suggesting that the survival of B. halimifolia may be limited by threshold values of salinity and waterlogging. With this study we want to raise awareness about the risk of replacement of estuarine subhalophilous communities by the ongoing invasion of B. halimifolia in Europe.     

Change in distribution of the vascular plant Sasa palmata in Sarobetsu Mire between 1977 and 2003

In recent decades, the extent of Sasa palmata-dominant communities has increased in Sarobetsu Mire in northern Hokkaido, Japan, replacing the original Sphagnum bog vegetation. However, this marked increase in distribution of Sasa in the mire has not been formally documented or investigated in detail. Using aerial photo-interpretation, the present study updated the distribution maps of Sasa communities, showing the changes that have occurred to these communities between 1977 and 2003. The results revealed that the extent of Sasa communities has increased by 15.8 % from 6.60 km² in 1977 to 7.64 km² in 2003. The most marked increase occurred on the ground associated with drainage channels, although the oldest channels were constructed more than half a century ago, suggesting that some responses to the drainage of peat bog ecosystems may take a considerable period of time before becoming particularly evident.     

Ectomycorrhizal fungal communities differ among parental and hybrid Populus cross types within a natural riparian habitat

Plant hybridization is common and important in ecological and economic contexts, however little is known about the impact of plant hybridization on ectomycorrhizal fungal (EMF) communities in natural habitats. We used a Populus hybrid system (P. angustifolia x P. fremontii) in a heterogeneous riparian landscape to address the hypothesis that EMF communities differ among hybrids and their parental species (cross types). Several key results emerged. (1) Cross type influenced EMF composition, with communities on hybrids being distinct from their parents. (2) Cross type influenced the composition of hyphal exploration types important for soil resource foraging, although contact and short distance exploration types were dominant on all cross types. (3) Cross type had a marginal influence on EMF colonization, with P. angustifolia highest and P. fremontii lowest. These results highlight the potential for tree hybridization to structure belowground communities in heterogeneous natural ecosystems.     

Possible interactions between bacterial diversity,microbial activity and supraglacial hydrology of cryoconite holes in Svalbard

The diversity of highly active bacterial communities in cryoconite holes on three Arctic glaciers in Svalbard was investigated using terminal restriction fragment length polymorphism (T-RFLP) of the 16S rRNA locus. Construction and sequencing of clone libraries allowed several members of these communities to be identified, with Proteobacteria being the dominant one, followed by Cyanobacteria and Bacteroidetes. T-RFLP data revealed significantly different communities in holes on the (cold) valley glacier Austre Brøggerbreen relative to two adjacent (polythermal) valley glaciers, Midtre Lovénbreen and Vestre Brøggerbreen. These population compositions correlate with differences in organic matter content, temperature and the metabolic activity of microbial communities concerned. No within-glacier spatial patterns were observed in the communities identified over the 2-year period and with the 1 km-spaced sampling. We infer that surface hydrology is an important factor in the development of cryoconite bacterial communities.     

Floodplain forests in Estonia: Typological diversity and growth conditions

Flooded forests in 79 sample areas were studied throughout the country. Using multivariate methods, six community types were established: (i)Tilia cordata-Mercurialis perennis, (ii)Ulmus laevis-Allium ursinum, (iii)Populus tremula-Convallaria majalis, (iv)Alnus incana-Cirsium oleraceum, (v)Alnus glutinosa-Filipendula ulmaria and, (vi)Alnus glutinosa-Carex acutiformis. The species composition of these types is partly overlapping but the abundance proportions of species are clearly different and all types have several significant (P < 0.05) indicator species. Communities of the first type grow mainly on temporarily overmoistened Dystri-Gleyic Arenosols on floodplain terraces but sometimes also in lower areas close to a riverbed on Eutric Gleysols or Gleyic Fluvisols. The second and third types embrace communities on levees where mainly Eutric Gleysols or Gleyic Fluvisols are represented. Communities of the fourth type are characteristic of low levees or flat areas with Mollic Fluvisols or Eutric Gleysols. The communities of the fifth and sixth types represent floodplain backswamp black alder forests on Eutric Gleysols, Molli-Histic and Histic Fluvisols. The convergence of communities, i.e., a situation where plant communities growing in various hydrological conditions and on different soils can have similar structure and belong to one community type is rather conspicuous for floodplain forests. In the conditions of Estonia, like in the Central European and Scandinavian countries, it is reasonable to consider as floodplain forest not only those growing on Fluvisolssensu stricto but all forests that are almost annually regularly covered with flood-water at least for a couple of weeks; the amount of alluvial sediments is not a decisive criterion in this case.     

The contest of microbial pigeon neighbors: Interspecies competition between Serratia marcescens and the human pathogen Cryptococcus neoformans

In nature, microorganisms often exhibit competitive behavior for nutrients and limited space, allowing them to alter the virulence determinants of pathogens. The human pathogenic yeast Cryptococcus neoformans can be found organized in biofilms, a complex community composed of an extracellular matrix which confers protection against predation. The aim of this study was to evaluate and characterize antagonistic interactions between two cohabiting microorganisms: C. neoformans and the bacteria Serratia marcescens. The interaction of S. marcescens with C. neoformans expressed a negative effect on biofilm formation, polysaccharide capsule, production of urease, and melanization of the yeast. These findings evidence that competition in mixed communities can result in dominance by one species, with direct impact on the physiological modulation of virulence determinants. Such an approach is key for understating the response of communities to the presence of competitors and, ultimately, rationally designing communities to prevent and treat certain diseases.