Biology subjects

Dittmar, T.

Publications and source records attributed to Dittmar, T..

8 recordsLinked to original sources

bioRxiv2026

Enhanced carbon storage in dissolved organic matter in a future oligotrophic ocean

Marine dissolved organic carbon (DOC) is one of the oceans largest carbon reser-voirs, which persists for millennia and exceeds the carbon stored in terrestrial and marine biomass combined (Hansell et al, 2012; Dittmar et al, 2021; Moran et al, 2022). Yet its response to climate change remains uncertain, largely because the ecological mechanisms behind its microbial degradation are poorly understood (Wagner et al, 2020; Legendre et al, 2015; Lonborg et al, 2020). Here we show how observed global-scale distribution of DOC emerges from bottom-up ecological controls acting on microbial DOC consumers. We combined large-scale metagenomic data (Larkin et al, 2021) with incubation experiments (Hale et al, 2017) to map global patterns of nutrient limitation in heterotrophic microbial communities responsible for DOC uptake. We then integrated a new microbial-DOC component into an Earth system model, which successfully reproduced observed global distributions of nutrient stress and DOC concentrations. Linking carbon and nutrient cycles reveals quantitatively significant consequences for the future ocean. Under a highemission scenario (SSP5-8.5), the DOC pool is projected to increase by 18-44 gigatons by 2200. This increase, driven by intensified nutrient limitation in surface waters, contributes substantially to the biological carbon pump, accounting for about[~] 30% of the increase in deep-ocean carbon storage associated with particulate organic carbon export. Overall, our results indicate that the marine DOC reservoir is more dynamic than previously thought. Reduced DOC remineralisation in an increasingly oligotrophic ocean constitutes a quantitatively significant negative feedback on centennial timescales.

microbiology↗

bioRxiv2025

Chemical diversity promotes ecosystem function

Nature benefits people in many ways that rely on how microorganisms and abiotic processes interact with organic matter to influence ecosystem function (EF). Despite many studies evaluating how biodiversity affects EF, most variation in EF remains unexplained. Here, we tested how the variety of organic compounds in the environment, termed chemodiversity, influences EF. Using a laboratory experiment and 101-lake survey spanning Europe, we discovered that chemodiversity, not biodiversity, consistently explained variation in multiple functions related to carbon cycling and ecosystem metabolism. We attributed positive chemodiversity-ecosystem multifunctionality relationships to the accumulation of compounds that could be biochemically transformed in more diverse ways at higher chemodiversity. We estimated chemodiversity will decline by 2100 due to changes in organic matter sources, causing European lakes to emit, on average, 1.6-times more carbon. These findings reframe our understanding of ecosystem functioning and suggest chemodiversity is key to sustain the benefits that nature delivers to people.

ecology↗

bioRxiv2024

Selective preservation of fucose-rich oligosaccharides in the North Atlantic Ocean

The ocean has a substantial capacity to store carbon dioxide fixed via photosynthesis in dissolved organic molecules. An estimated 20% of the 660 Gt dissolved organic carbon in the ocean pool consists of structurally uncharacterized oligosaccharides, which appear to resist microbial degradation (Aluwihare et al., 1997). Current technologies lack the sensitivity and molecular resolution to identify these oligosaccharides. Here, we adapted graphitized carbon chromatography to extract and separate marine oligosaccharides for liquid chromatography high resolution mass spectrometry analysis. Using a newly-developed de novo annotation tool, we found 110 oligosaccharide structures in surface and deep ocean seawater at two distant locations in the North Atlantic Ocean. One group of the detected oligosaccharides was found only in surface seawater and consisted of larger and more abundant molecules detected by our analysis. A second group of smaller, less abundant oligosaccharides was detected in both the surface and deep ocean seawater of both sampled locations. The composition of oligosaccharides differed between the surface and deep ocean, with deep ocean samples relatively enriched in hard-to-metabolize deoxy-sugars, and xylose, amino sugars and uronic acids compared to simple hexoses. Notably the deoxy-sugar fucose constituted 35-40% of the monomers in deep-sea oligosaccharides, twice the percentage in surface ocean oligosaccharides. The ubiquity of deep ocean oligosaccharides indicates that they represent a preserved fraction of the carbohydrate pool. Their enrichment in specific monosaccharides suggests selective preservation of fucose-rich oligosaccharides in the deep ocean.

ecology↗

bioRxiv2023

Logging disrupts the ecology of molecules in headwater streams

Global demand for wood products is increasing forest harvest. One understudied consequence of logging is that it accelerates mobilization of dissolved organic matter (DOM) from soils to aquatic ecosystems. Here, we tested how logging changed DOM in headwaters of hardwood-dominated catchments in northern Ontario, Canada. We apply a before-after control-impact experiment across four catchments for three years. DOM concentration in streams from logged catchments quadrupled, on average, after the first year post-harvest, but resulting changes to the molecular composition of DOM persisted for at least two-years. Ultrahigh-resolution mass spectrometry revealed that DOM within logged catchments was more energy-rich and chemically diverse than in controls, with novel highly unsaturated polyphenols, carboxylic-rich alicyclic, and nitrogen-containing formulae. The molecular composition of stream DOM measured fortnightly post-harvest was most strongly associated with DOM composition within intermediate and deeper layers of contributing soils, likely due to increased hydrological connectivity post-harvest. We estimate logging increased the total annual flux of dissolved organic carbon in streams by 6.4% of extracted wood carbon, and this carbon was more likely to be released into the atmosphere. Carbon accounting of forestry, including as a natural climate solution, must now consider the transport and fate of DOM from land into water.

ecology↗

bioRxiv2022

Universal microbial reworking of dissolved organic matter along environmental gradients

Soils are losing increasing amounts of carbon annually to freshwaters as dissolved organic matter (DOM), which, if degraded, can accelerate climate change. DOM is more susceptible to degradation closer to its source and becomes increasingly dominated by the same, difficult-to-degrade compounds as degradation proceeds. However, the processes underlying DOM degradation across environments are poorly understood. Here we found DOM changed similarly along soil-aquatic gradients irrespective of differences in environmental conditions. Using ultra-high-resolution mass spectrometry, we tracked DOM along soil depths and hillslope positions in forest headwater catchments and related its composition to soil microbiomes and physical chemistry. Along depths and hillslopes, carbohydrate-like and unsaturated hydrocarbon-like compounds increased in mass, suggestive of microbial reworking of plant material. More than half of the variation in the abundance of these compounds was related to the expression of genes essential for degrading plant-derived carbohydrates. Our results implicate continuous microbial reworking in shifting DOM towards universal compounds in soils. By synthesising data from the land-to-ocean continuum, we suggest these processes can generalise across ecosystems and spatiotemporal scales. Such general degradation patterns can be leveraged to predict DOM composition and its downstream reactivity along environmental gradients to inform management of soil-to-stream carbon losses.

ecology↗

bioRxiv2022

Growth, organic matter release, aggregation and recycling during a diatom bloom: A model-based analysis of a mesocosm experiment

Mechanisms terminating phytoplankton blooms are often not well understood. Potentially involved processes such as consumption by grazers, flocculation, and viral lysis each have different post-bloom consequences on the processing of the organic material, therefore it is important to develop a better understanding of the relevance of these processes, and potential interactions between them. In this study, we present a model-based analysis of a spring bloom observed in a mesocosm experiment. The intermediate-complexity (27-state variable) numerical model we extended from an earlier version to this end can resolve C, N, P and Si cycles, and relevant processes like formation of various organic material size classes (low and high molecular weight (hereafter small and large) dissolved organic carbon (DOC), transparent exopolymer particles (TEP), and small/large detritus) and their degradation by two bacterial sub-communities (free-living and particle-attached) and planktonic protists (heterotrophic flagellates and ciliates). The model can explain > 90% of the variation of a rich set of observations consisting of 11 independent variables over the course of 13 days during which a bloom largely dominated by diatoms develops, and disappears almost entirely. Fluxes estimated by the model point to the importance of coagulation (TEP formation) as a sink term for DOC, and a source term for POC. Consequently, aggregation with TEPs constitute an important loss term for phytoplankton. The flocculated phytoplankton, and detrital material, in turn become rapidly degraded by the particle attached bacteria and other protist heterotrophs. Through a scenario analysis, the relevance of nutrient-stress enhanced lysis rates; alterations between small and large DOC in phytoplankton exudates; and coagulation of smaller DOC molecules were investigated. Our results suggest that the former two processes have negligible effects in isolation, but when combined with the latter, they can synergistically cause substantial deviations in TEP formation, hence, in flocculation rates; and consequently in the peak magnitude of the diatom bloom, and in timing of its termination. Our results point to a need for better understanding of processes governing the termination of phytoplankton blooms, their inter-dependencies, and consequences on the global biogeochemical cycles.

microbiology↗

bioRxiv2019

Ammonia-oxidizing archaea release a suite of organic compounds potentially fueling prokaryotic heterotrophy in the ocean

Ammonia-oxidizing archaea (AOA) constitute a considerable fraction of microbial biomass in the global ocean, comprising 20-40% of the oceans prokaryotic plankton and thus play an important role in global nitrogen cycle. However, it remains enigmatic to what extent these chemolithoautotrophic archaea are releasing dissolved organic matter (DOM). A combination of targeted and untargeted metabolomics was used to characterise the exometabolomes of three model AOA strains of the Nitrosopumilus genus. Furthermore, we compared the composition of intra- and extracellular dissolved free amino acids (DFAA). Our results indicate that marine AOA exude a suite of organic compounds with potentially varying reactivity, dominated by nitrogen-containing compounds. A significant fraction of the released DOM consisted of labile compounds, which typically limit prokaryotic heterotrophic activity in open ocean waters, including amino acids, thymidine and B vitamins. In growing Nitrosopumilus cultures, hydrophobic amino acids were likely released as a result of passive diffusion corresponding to ammonia oxidation activity, while glycine was continuously released at high rates. Our results suggest that AOA release several ecologically and biochemically relevant metabolites, potentially fueling heterotrophic prokaryotes in the ocean.

ecology↗

bioRxiv2017

Bottled aqua incognita: Microbiota assembly and dissolved organic matter diversity in natural mineral waters

BackgroundNon-carbonated natural mineral waters contain microorganisms that regularly grow after bottling despite low concentrations of dissolved organic matter (DOM). Yet, the compositions of bottled water microbiota and organic substrates that fuel microbial activity, and how both change after bottling, are still largely unknown.\n\nResultsWe performed a multifaceted analysis of microbiota and DOM diversity in twelve natural mineral waters from six European countries. 16S rRNA gene-based analyses showed that less than ten species-level operational taxonomic units (OTUs) dominated the bacterial communities in the water phase and associated with the bottle wall after a short phase of post-bottling growth. Members of the betaproteobacterial genera Curvibacter, Aquabacterium, and Polaromonas (Comamonadaceae) grew in most waters and represent ubiquitous, mesophilic, heterotrophic aerobes in bottled waters. Ultrahigh-resolution mass spectrometry of DOM in bottled waters and their corresponding source waters identified thousands of molecular formulae characteristic of mostly refractory, soil-derived DOM.\n\nConclusionsThe bottle environment, including source water physicochemistry, selected for growth of a similar low-diversity microbiota across various bottled waters. Relative abundance changes of hundreds of multi-carbon molecules were related to growth of less than ten abundant OTUs. We thus speculate that individual bacteria cope with oligotrophic conditions by simultaneously consuming diverse DOM molecules.

microbiology↗