Refine
Language
- English (8)
Is part of the Bibliography
- yes (8)
Keywords
- European Multi Lake Survey (2)
- anatoxin (2)
- cylindrospermopsin (2)
- direct effects (2)
- indirect effects (2)
- microcystin (2)
- spatial distribution (2)
- temperature (2)
- Aquatic fungi (1)
- Aquifers (1)
- CDOM (1)
- Climate-change ecology (1)
- DOC (1)
- Groundwater (1)
- Humic acids (1)
- Limnology (1)
- Water resources (1)
Institute
The ecological relevance of fungi in freshwater ecosystems is becoming increasingly evident, particularly in processing the extensive amounts of polymeric organic carbon such as cellulose, chitin, and humic substances (HS). We isolated several fungal strains from oligo-mesotrophic Lake Stechlin, Brandenburg, Germany, and analyzed their ability to degrade polymeric-like substrates. Using liquid chromatography-organic carbon detection, we determined the byproducts of HS transformation by the freshwater fungus Cladosporium sp. KR14. We demonstrate the ability of this fungus to degrade and simultaneously synthesize HS, and that transformation processes were intensified when iron, as indicator of the occurrence of Fenton reactions, was present in the medium. Furthermore, we showed that structural complexity of the HS produced changed with the availability of other polymeric substances in the medium. Our study highlights the contribution of freshwater Ascomycetes to the transformation of complex organic compounds. As such, it has important implications for understanding the ecological contribution of fungi to aquatic food webs and related biogeochemical cycles.
Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.
Under ongoing climate change and increasing anthropogenic activity, which continuously challenge ecosystem resilience, an in-depth understanding of ecological processes is urgently needed. Lakes, as providers of numerous ecosystem services, face multiple stressors that threaten their functioning. Harmful cyanobacterial blooms are a persistent problem resulting from nutrient pollution and climate-change induced stressors, like poor transparency, increased water temperature and enhanced stratification. Consistency in data collection and analysis methods is necessary to achieve fully comparable datasets and for statistical validity, avoiding issues linked to disparate data sources. The European Multi Lake Survey (EMLS) in summer 2015 was an initiative among scientists from 27 countries to collect and analyse lake physical, chemical and biological variables in a fully standardized manner. This database includes in-situ lake variables along with nutrient, pigment and cyanotoxin data of 369 lakes in Europe, which were centrally analysed in dedicated laboratories. Publishing the EMLS methods and dataset might inspire similar initiatives to study across large geographic areas that will contribute to better understanding lake responses in a changing environment.
There is now increasing evidence for the importance of microbial regulation of biogeochemical cycling in streams. Resource availability shapes microbial community structure, but less is known about how landscape-mediated availability of nutrients and carbon can control microbial functions in streams. Using comparative metagenomics, we examined the relationship between microbial functional genes and composition of dissolved organic matter (DOM), nutrients, and suspended microbial communities in 11 streams, divided into three groups based on the predominant land cover category (agriculture, forested, or wetland). Using weighted gene co-occurrence network analysis, we identified clusters of functions related to DOM composition, agricultural land use, and/or wetland and forest land cover. Wetland-dominated streams were characterized by functions related to nitrogen metabolism and processing of aromatic carbon compounds, with strong positive correlations with dissolved organic carbon concentration and DOM aromaticity. Forested streams were characterized by metabolic functions related to monomer uptake and carbohydrates, such as mannose and fructose metabolism. In agricultural streams, microbial functions were correlated with more labile, protein-like DOM, PO4, and NO3, likely reflecting functional adaptation to labile DOM and higher nutrient concentrations. Distinct changes in the functional composition and loss of functional diversity of microorganisms became evident when comparing natural to agricultural catchments. Although all streams showed signs of functional redundancy, loss of species richness per function in agricultural catchments suggests that microbial functions in natural catchments may be more resilient to disturbance. Our results provide new insight into microbial community functions involved in nutrient and carbon biogeochemical cycles and their dependence on specific environmental settings.
Non-predatory mortality of zooplankton provides an abundant, yet, little studied source of high quality labile organic matter (LOM) in aquatic ecosystems. Using laboratory microcosms, we followed the decomposition of organic carbon of fresh C-13-labelled Daphnia carcasses by natural bacterioplankton. The experimental setup comprised blank microcosms, that is, artificial lake water without any organic matter additions (B), and microcosms either amended with natural humic matter (H), fresh Daphnia carcasses (D) or both, that is, humic matter and Daphnia carcasses (HD). Most of the carcass carbon was consumed and respired by the bacterial community within 15 days of incubation. A shift in the bacterial community composition shaped by labile carcass carbon and by humic matter was observed. Nevertheless, we did not observe a quantitative change in humic matter degradation by heterotrophic bacteria in the presence of LOM derived from carcasses. However, carcasses were the main factor driving the bacterial community composition suggesting that the presence of large quantities of dead zooplankton might affect the carbon cycling in aquatic ecosystems. Our results imply that organic matter derived from zooplankton carcasses is efficiently remineralized by a highly specific bacterial community, but does not interfere with the bacterial turnover of more refractory humic matter.
Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.
Studies on the ecological role of fungi and, to a lesser extent, oomycetes, are receiving increasing attention, mainly due to their participation in the cycling of organic matter in aquatic ecosystems. To unravel their importance in humification processes, we isolated several strains of fungi and oomycetes from Anzali lagoon, Iran. We then performed taxonomic characterization by morphological and molecular methods, analyzed the ability to degrade several polymeric substrates, performed metabolic fingerprinting with Ecoplates, and determined the degradation of humic substances (HS) using liquid chromatography-organic carbon detection. Our analyses highlighted the capacity of aquatic fungi to better degrade a plethora of organic molecules, including complex polymers. Specifically, we were able to demonstrate not only the utilization of these complex polymers, but also the role of fungi in the production of HS. In contrast, oomycetes, despite some morphological and physiological similarities with aquatic fungi, exhibited a propensity toward opportunism, quickly benefitting from the availability of small organic molecules, while exhibiting sensitivity toward more complex polymers. Despite their contrasting roles, our study highlights the importance of both oomycetes and fungi in aquatic organic matter transformation and cycling with potential implications for the global carbon cycle.
Fungi are an important component of microbial communities and are well known for their ability to decompose refractory, highly polymeric organic matter. In soils and aquatic systems, fungi play an important role in carbon processing, however, their diversity, community structure and function as well as ecological role, particularly in groundwater, are poorly studied. The aim of this study was to examine the fungal community composition, diversity and function in groundwater from 16 boreholes located in the vicinity of two lakes in NE Germany that are characterized by contrasting trophic status. The analysis of 28S rRNA gene sequences amplified from the groundwater revealed high fungal diversity arid clear differences in community structure between the aquifers. Most sequences were assigned to Ascomycota and Basidiomycota, but members of Chytridiomycota, Cryptomycota, Zygomycota, Blastocladiomycota, Glomeromycota and Neocallimastigomycota were also detected. In addition, 27 species of fungi were successfully isolated from the groundwater samples and tested for their ability to decompose complex organic polymers - the predominant carbon source in the groundwater. Most isolates showed positive activities for at least one of the tested polymer types, with three strains, belonging to the genera Gibberella, Isaria and Cadophora, able to decompose all tested substrates. Our results highlight the high diversity of fungi in groundwater, and point to their important ecological role in breaking down highly polymeric organic matter in these isolated microbial habitats. (C) 2019 Elsevier Ltd and British Mycological Society. All rights reserved.