File Name: patterns in dissolved organic matter lability and consumption across aquatic ecosystems.zip
Global change impacts on marine biogeochemistry will be partly mediated by heterotrophic bacteria. Besides ocean warming, future environmental changes have been suggested to affect the quantity and quality of organic matter available for bacterial growth. However, it is yet to be determined in what way warming and changing substrate conditions will impact marine heterotrophic bacteria activity. Our study shows that DOC source had the largest effect on the measured bacterial response, but this response was amplified by increasing temperature. We specifically demonstrate that 1 extracellular enzymatic activity and DOC consumption increased with warming, 2 this enhanced DOC consumption did not result in increased biomass production, since the increases in respiration were larger than for bacterial growth with warming, and 3 different DOC bioavailability affected the magnitude of the microbial community response to warming.
We examined microbial assemblages from habitats fed by glacial meltwater within the McMurdo Dry Valleys, Antarctica and on the west Greenland Ice Sheet GrIS , evaluating potential physicochemical factors explaining trends in community structure. Microbial assemblages present in the different Antarctic dry valley habitats were dominated by Sphingobacteria and Flavobacteria , while Gammaproteobacteria and Sphingobacteria prevailed in west GrIS supraglacial environments.
Community dissimilarities were strongly correlated with dissolved organic matter DOM quality. Microbial meltwater assemblages were most closely associated with different protein-like components of the DOM pool. Microbes in environments with mineral particles i. Our results demonstrate the establishment of distinct microbial communities within ephemeral glacial meltwater habitats, with DOM-microbe interactions playing an integral role in shaping communities on local and polar spatial scales.
These icy environments are subject to relatively similar environmental conditions, including low temperature, frequent freeze-thaw cycles, seasonally low water availability, desiccation and nutrient limitation, but vary in the degree of surface melt and geochemical composition.
As such, the presence of distinct microbial communities in environmentally similar glacial meltwater habitats Cameron et al. While regional differences across glacial meltwater communities have been frequently attributed to local aeolian deposition, catchment geology, and physical and geographical variables Cameron et al. Dissolved organic matter DOM on ice sheets originates from a variety of allochthonous i.
However, the mechanism by which the composition of DOM influences bacterial utilization and ultimately community composition is largely unknown. Given the habitat-specific selective pressures of cryo-environments, we hypothesize that bacterial assemblages are shaped by geochemistry, which provides the available energy sources necessary to support life. Meltwater samples were collected from two glaciers in the McMurdo Dry Valleys, Antarctica, stream water, stream sediments, glacial ice, snow, and cryoconite holes and from the western margin of the Greenland Ice Sheet GrIS supraglacial lakes and cryoconite holes.
Illumina MiSeq 16S rRNA gene amplicons were analyzed to assess differences in community structure across and within these environments. Geochemical parameters, including major ions, nutrients, DOC concentration, and fluorescing DOM characteristics were evaluated to infer their influence on microbial community composition.
The primary objective of this study was to link trends in bacterial biodiversity to DOM quality across glacial systems, thus enabling better predictions regarding their function in the context of a changing environment. This barren region experiences katabatic winds originating in the continental interior, which are important in controlling local climate, physical weathering and material transport. Sediments are primarily located on the lateral margins of the stream, and herein referred to as parafluvial sediments.
More information on sampling regime is provided below and in Table S1 Supporting Information. Temperature, pH, conductivity, dissolved oxygen, and total dissolved solids in the two Antarctic streams were measured on site using a Manta Sub2 probe Eureka Water Probes Inc. A malfunction of the probe obstructed in situ measurements in west GrIS supraglacial environments. Sediment 20—30 g and freshly fallen snow samples were aseptically collected with sterile spatulas. Meltwater samples 0.
Samples for microbial community analysis from supraglacial lakes on the west GrIS were collected on polyethersulfone 0. Between 0. Geochemical data were statistically analyzed to identify differences across samples, using a general linear model of analysis of variance ANOVA in version 17, Minitab Inc.
DOM is comprised of a heterogeneous mixture of organic compounds, with the analysis of fluorescent components proven to be useful in assessing its chemical quality Cory and McKnight ; Fellman et al.
Due to large difference in characteristics of the fluorescent fraction of DOM between the Antarctic and Arctic samples e. In light of these restrictions we quantified the EEMs spectra based on characteristic fluorescence peaks Coble ; Fellman et al. Fluorescence intensity F. Forward and reverse sequences were joined with the Quantitative Insights Into Microbial Ecology toolkit version 1.
Contigs were subsequently analyzed with the Mothur platform v. Any OTU found in the blank samples were removed from corresponding sequence libraries. Precipitation events are rare in polar deserts; thus, with only single snow samples collected, these were excluded from subsequent statistical analysis. Large R values close to 1 indicate that two samples are highly dissimilar, while small R values close to zero signify little or no dissimilarity.
Both Antarctic streams had low ionic strength mean Fluorescence in the humic-like regions of the EEMs was apparent in all samples; however, only the fluorescence spectra of Canada Stream water DOM resolved in distinct humic fluorophores.
Change in the relative abundance of fluorescent intensity F. The observed number of OTUs across all sampled habitats showed similar patterns when compared to the predicted alpha diversity indices Fig. S1, Supporting Information. Based on Chao richness, the greatest diversity was found in the Canada Stream water Species richness for Antarctic stream sediments, ice and cryoconite hole communities was between The lowest species richness was calculated for west GrIS supraglacial lakes Antarctic environments shared Within each clade, sample types clustered into their own representative group, with the exception of one CG sediment sample that grouped more closely with the Canada Glacier samples.
Overlap was found between CG ice and CG stream samples. Relative abundance of MiSeq 16S rRNA gene sequences representing the distribution of microbial assemblages with individual samples grouped together based on sampling location. Percentages are reported at the class taxonomic level. Markedly, OTU profiles found in similar environments i.
With a focus on the most abundant OTUs in each sample, dissimilarities were largely attributed to four families i. Combined with the unclassified microbial realm 7. These four families also explained An initial CCA between CG stream and Canada Stream water OTU profiles and the physicochemical dataset was performed to determine whether environmental variables had an effect on microbial assemblage composition. However, variables tested temperature, pH, dissolved oxygen, conductivity, major cations and anions, and DOC concentrations were statistically insignificant in explaining assemblage composition.
The established model explained The first axis explained Microbial assemblages from the west GrIS clustered closely together and were best explained by the protein-like component B1. Canada Stream microbial assemblages were clearly described by the presence of humic-like fractions of DOM.
Phylotype composition from Canada Stream sediment, Canada Glacier cryoconite holes, and CG sediment samples were moderately influenced by humic- and protein-like DOM constituents. Different colored circles represent relative fluorescence intensities for fluorophores commonly observed in natural waters Coble from each sample. Fluorescence from protein-like OM components are represented as B1 and B2 tyrosine-like and T1 and T2 tryptophan-like.
Fluorescent humic-like OM components are represented by A and C. Individual microbial assemblages clustered based on location i. Nonetheless, dominant microbial phylotypes in snow on polar ice sheets i. Relevant to the discussion on community establishment and stability in glacial meltwater habitats, our study provides evidence that microbial assemblages from samples within the same local environment exhibit a high degree of dissimilarity in compartments along the hydrologic flow path i.
Similar to previous reports of glacial meltwater habitats i. Despite the predominance of protein-like components, there was little to no overlap in the overall DOM composition across investigated habitats. In contrast to the terrestrial Canada Stream, the CG supraglacial stream was largely devoid of benthic substrates and microbial mats, features reflective of the overall DOM composition.
Conversely, the presence of both protein- and humic-like fluorescence in the Canada stream DOM is typical of Antarctic streams with inter-annual DOM accumulation by microbial mats McKnight and Tate , characteristics also expressed in habitats shaped by the deposition of terrestrial mineral particles i.
CG parafluvial sediments and cryoconite. In each habitat, microbial assemblages were associated with either specific protein-like or humic-like fluorophores, with the calculated correlations between DOM components and OTUs of heterotrophic bacteria suggestive of contrasting taxonomic DOM preferences Fig.
Specifically, diverse lineages within the Bacteroidetes , the most dominant members in all dry valley samples, are well known for degrading high molecular weight organic matter i. This class of Proteobacteria is generally known to be comprised of fast-growing opportunists Pinhassi and Berman ; Pernthaler and Amann Further, Gammaproteobacteria have a competitive advantage in phosphate-limited environments Ho et al.
Intricate substrate dependencies on specific DOM fluorophores have been shown for major taxonomic groups within many aquatic communities e. Evidence presented here establishes causality between DOM substrate composition and microbial community composition Fig.
Therefore, changes in DOM composition may result in dramatic shifts in the functional response of these glacial meltwater microbial systems, with subsequent consequences for downstream environments through alterations in the geochemical composition of fluxes.
Here we demonstrate that DOM composition has a major effect on glacial surface microbial communities, and by extension, influences ecosystem function. Additionally, our data contribute to the growing evidence that supraglacial habitats harbor spatially variable communities governed by local environmental factors Cameron et al. The authors wish to thank the members of the Cotton Glacier and Greenland field teams, the Antarctic and Arctic support contractors and the pilots and crew of Petroleum Helicopters Inc.
Any opinions, findings, or conclusions expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation NSF. Strong linkages between DOM optical properties and main clades of aquatic bacteria. Limnol Oceanogr. Google Scholar. High microbial activity on glaciers: importance to the global carbon cycle. Global Change Biol.
Glaciers and ice sheets as a biome. Trends Ecol Evol. The microbiome of glaciers and ice sheets. NPJ Biofilms Microbiomes. Origin and sources of dissolved organic matter in snow on the East Antarctic ice sheet. Environ Sci Technol. Microbial communities associated with Antarctic snow pack and their biogeochemical implications. Microbiol Res. Molecular insights on dissolved organic matter transformation by supraglacial microbial communities.
Modeling supraglacial water routing and lake filling on the Greenland Ice Sheet. J Geophys Res Earth Surf. Changes in dissolved organic matter DOM fluorescence in proglacial Antarctic streams.
Abundance and dynamics of dissolved organic carbon in glacier systems.
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Dissolved organic carbon and bioavailability of N and P as indicators of soil quality. Maria Lucia Azevedo Silveira. Soil quality has become an important issue in soil science. Considerable attempts have been made to define soil quality, but a general concept has not yet been accepted by the scientific community. The selection of quantitative indices for soil quality is extremely difficult, and a considerable number of chemical, physical, and biochemical properties have been suggested as potential indicators of soil quality. Because soil organic matter SOM can be associated with different soil chemical, physical and biological processes, it has been widely considered as one of the best soil quality indicator.
Bacteria play a key role in the planetary carbon cycle partly because they rapidly assimilate labile dissolved organic matter DOM in the ocean. However, knowledge of the molecular mechanisms at work when bacterioplankton metabolize distinct components of the DOM pool is still limited. We, therefore, conducted seawater culture enrichment experiments with ecologically relevant DOM, combining both polymer and monomer model compounds for distinct compound classes. This included carbohydrates polysaccharides vs. We noted pronounced changes in bacterial growth, activity, and transcription related to DOM characteristics. Moreover, we found a strong divergence in functional transcription at the level of particular monomers and polymers i. These specific responses included a variety of cellular and metabolic processes that were mediated by distinct bacterial taxa, suggesting pronounced functional partitioning of organic matter.
We examined microbial assemblages from habitats fed by glacial meltwater within the McMurdo Dry Valleys, Antarctica and on the west Greenland Ice Sheet GrIS , evaluating potential physicochemical factors explaining trends in community structure. Microbial assemblages present in the different Antarctic dry valley habitats were dominated by Sphingobacteria and Flavobacteria , while Gammaproteobacteria and Sphingobacteria prevailed in west GrIS supraglacial environments. Community dissimilarities were strongly correlated with dissolved organic matter DOM quality. Microbial meltwater assemblages were most closely associated with different protein-like components of the DOM pool. Microbes in environments with mineral particles i.
Special issue: Interactions between planktonic organisms and biogeochemical Research article 15 Jan Correspondence : Christos Panagiotopoulos christos.
Start Search. Search Results. Hits on this site 0 All results within Lund University The character and quantity of dissolved organic carbon DOC were studied in nine small boreal streams and adjacent soils during two years, with focus on the spring snowmelt period. The streams cover a forest-wetland gradient, spanning….
The marine dissolved organic carbon DOC pool is an important player in the functioning of marine ecosystems. A unified outcome of the future impacts of these stressors on the global ocean DOC production and degradation is not possible, due to regional differences and differences in stressors impacts, but general patterns for each stressor are presented. Therefore, changes in DOC cycling due to global change, can result in alterations in the air-sea exchange of CO 2 , and have the potential to create important feedbacks onto global change itself.
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Inputs of dissolved organic carbon DOC to lakes derived from the surrounding landscape can be stored, mineralized or passed to downstream ecosystems. The balance among these OC fates depends on a suite of physical, chemical, and biological processes within the lake, as well as the degree of recalcintrance of the allochthonous DOC load. The relative importance of these processes has not been well quantified due to the complex nature of lakes, as well as challenges in scaling DOC degradation experiments under controlled conditions to the whole lake scale. We used a coupled hydrodynamic-water quality model to simulate broad ranges in lake area and DOC, two characteristics important to processing allochthonous carbon through their influences on lake temperature, mixing depth and hydrology. For each lake, we tested several mineralization rates range: 0. We found that mineralization rates at the ecosystem scale were roughly half the values from laboratory experiments, due to relatively cool water temperatures and other lake-specific factors that influence water temperature and hydrologic residence time.
Collin P. E-mail: cward whoi. E-mail: rmcory umich. In sunlit waters, photodegradation of dissolved organic matter DOM yields completely oxidized carbon i. Of these two groups of DOM photo-products, more studies focus on CO 2 a greenhouse gas than on partially oxidized DOM, which is likely a diverse group of compounds with poorly constrained roles in aquatic carbon cycling or biogeochemistry. The objective of this study is to address knowledge gaps on the prevalence, products, and pathways of DOM partial photo-oxidation. Here we traced the photochemical incorporation of isotopically labelled 18 O 2 into DOM isolated from Alaskan Arctic surface waters using high-resolution mass spectrometry.
In this study, we experimentally investigated the degradation of dissolved organic matter DOM during lateral and vertical mixing of different water masses in a peri-alpine lake. River intrusions and vertical winter turnover in Lake Geneva Switzerland, France were simulated through short-term laboratory incubations by mixing riverine and lacustrine waters or lacustrine waters collected at different depths in winter.
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