| 1. |
- Wituschek, Andreas, et al.
(author)
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High-gain harmonic generation with temporally overlapping seed pulses and application to ultrafast spectroscopy
- 2020
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In: Optics Express. - 1094-4087. ; 28, s. 29976-90
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Journal article (peer-reviewed)abstract
- Collinear double-pulse seeding of the High-Gain Harmonic Generation (HGHG) process in a free-electron laser (FEL) is a promising approach to facilitate various coherent nonlinear spectroscopy schemes in the extreme ultraviolet (XUV) spectral range. However, in collinear arrangements using a single nonlinear medium, temporally overlapping seed pulses may introduce nonlinear mixing signals that compromise the experiment at short time delays. Here, we investigate these effects in detail by extending the analysis described in a recent publication (Wituschek et al., Nat. Commun., 11, 883, 2020). High-order fringe-resolved autocorrelation and wave packet interferometry experiments at photon energies > 23 eV are performed, accompanied by numerical simulations. It turns out that both the autocorrelation and the wave-packet interferometry data are very sensitive to saturation effects and can thus be used to characterize saturation in the HGHG process. Our results further imply that time-resolved spectroscopy experiments are feasible even for time delays smaller than the seed pulse duration.
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| 2. |
- Wituschek, Andreas, et al.
(author)
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Tracking attosecond electronic coherences using phase-manipulated extreme ultraviolet pulses
- 2020
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 11
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Journal article (peer-reviewed)abstract
- The recent development of ultrafast extreme ultraviolet (XUV) coherent light sources bears great potential for a better understanding of the structure and dynamics of matter. Promising routes are advanced coherent control and nonlinear spectroscopy schemes in the XUV energy range, yielding unprecedented spatial and temporal resolution. However, their implementation has been hampered by the experimental challenge of generating XUV pulse sequences with precisely controlled timing and phase properties. In particular, direct control and manipulation of the phase of individual pulses within an XUV pulse sequence opens exciting possibilities for coherent control and multidimensional spectroscopy, but has not been accomplished. Here, we overcome these constraints in a highly time-stabilized and phase-modulated XUV-pump, XUV-probe experiment, which directly probes the evolution and dephasing of an inner subshell electronic coherence. This approach, avoiding any XUV optics for direct pulse manipulation, opens up extensive applications of advanced nonlinear optics and spectroscopy at XUV wavelengths.
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| 3. |
- Bruder, Andreas, et al.
(author)
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Biotic interactions modify multiple-stressor effects on juvenile brown trout in an experimental stream food web
- 2017
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In: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 23:9, s. 3882-3894
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Journal article (peer-reviewed)abstract
- Agricultural land use results in multiple stressors affecting stream ecosystems. Flow reduction due to water abstraction, elevated levels of nutrients and chemical contaminants are common agricultural stressors worldwide. Concurrently, stream ecosystems are also increasingly affected by climate change. Interactions among multiple co-occurring stressors result in biological responses that cannot be predicted from single-stressor effects (i.e. synergisms and antagonisms). At the ecosystem level, multiple-stressor effects can be further modified by biotic interactions (e.g. trophic interactions). We conducted a field experiment using 128 flow-through stream mesocosms to examine the individual and combined effects of water abstraction, nutrient enrichment and elevated levels of the nitrification inhibitor dicyandiamide (DCD) on survival, condition and gut content of juvenile brown trout and on benthic abundance of their invertebrate prey. Flow velocity reduction decreased fish survival (−12% compared to controls) and condition (−8% compared to initial condition), whereas effects of nutrient and DCD additions and interactions among these stressors were not significant. Negative effects of flow velocity reduction on fish survival and condition were consistent with effects on fish gut content (−25% compared to controls) and abundance of dominant invertebrate prey (−30% compared to controls), suggesting a negative metabolic balance driving fish mortality and condition decline, which was confirmed by structural equation modelling. Fish mortality under reduced flow velocity increased as maximal daily water temperatures approached the upper limit of their tolerance range, reflecting synergistic interactions between these stressors. Our study highlights the importance of indirect stressor effects such as those transferred through trophic interactions, which need to be considered when assessing and managing fish populations and stream food webs in multiple-stressor situations. However, in real streams, compensatory mechanisms and behavioural responses, as well as seasonal and spatial variation, may alter the intensity of stressor effects and the sensitivity of trout populations.
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| 4. |
- Bruder, Andreas, et al.
(author)
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Multiple-stressor effects on leaf litter decomposition and fungal decomposers in agricultural streams contrast between litter species
- 2016
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In: Functional Ecology. - : John Wiley & Sons. - 0269-8463 .- 1365-2435. ; 30:7, s. 1257-1266
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Journal article (peer-reviewed)abstract
- Agricultural land use commonly exerts multiple stressors on the functioning of stream ecosystems, including leaf litter decomposition and the utilization of this resource in stream food webs. If stressors interact, their cumulative effects on biotic responses cannot be predicted from knowledge of individual stressor effects, posing challenges for management and restoration of ecosystems. We examined the individual and interactive effects of four common agricultural stressors and the role of litter quality on leaf litter decomposition and fungal decomposers. In 128 outdoor, flow-through mesocosms, we manipulated levels of nutrients, a nitrification inhibitor (dicyandiamide), deposited fine sediment and flow velocity. Interactions among these stressors can ensue because, for instance, they jointly affect physicochemical conditions around leaf litter colonized by fungi such as concentrations of dissolved oxygen and nutrients. The two litter species used, deciduous birch and evergreen mahoe, showed contrasting decomposition dynamics, and these differences influenced their response to stressors. Fungi were important for birch litter decomposition but played a minor role for mahoe. Overall, flow velocity reduction and deposited fine sediment had the strongest, mainly negative effects on fungi and litter decomposition, probably as a consequence of reductions in dissolved oxygen available to fungi. However, fine sediment substantially increased mahoe litter mass loss, pointing at fungi-independent processes being relevant for its decomposition. Although interactions among stressors were uncommon, they showed effects of the same magnitude as stressor main effects. Potential mechanisms underlying interactions included reductions in dissolved oxygen and changes in microbial community composition. Knowledge of the effects of multiple agricultural stressors and of litter quality on litter decomposition and litter-associated fungi is crucial for management of forested riparian corridors, which have been shown to efficiently mitigate impacts of agricultural stressors on streams. The contrasting responses of the litter species used in our study warrant consideration of species composition of the riparian vegetation.
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| 5. |
- Costello, David M., et al.
(author)
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Global patterns and controls of nutrient immobilization on decomposing cellulose in riverine ecosystems
- 2022
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In: Global Biogeochemical Cycles. - : John Wiley & Sons. - 0886-6236 .- 1944-9224. ; 36:3
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Journal article (peer-reviewed)abstract
- Microbes play a critical role in plant litter decomposition and influence the fate of carbon in rivers and riparian zones. When decomposing low-nutrient plant litter, microbes acquire nitrogen (N) and phosphorus (P) from the environment (i.e., nutrient immobilization), and this process is potentially sensitive to nutrient loading and changing climate. Nonetheless, environmental controls on immobilization are poorly understood because rates are also influenced by plant litter chemistry, which is coupled to the same environmental factors. Here we used a standardized, low-nutrient organic matter substrate (cotton strips) to quantify nutrient immobilization at 100 paired stream and riparian sites representing 11 biomes worldwide. Immobilization rates varied by three orders of magnitude, were greater in rivers than riparian zones, and were strongly correlated to decomposition rates. In rivers, P immobilization rates were controlled by surface water phosphate concentrations, but N immobilization rates were not related to inorganic N. The N:P of immobilized nutrients was tightly constrained to a molar ratio of 10:1 despite wide variation in surface water N:P. Immobilization rates were temperature-dependent in riparian zones but not related to temperature in rivers. However, in rivers nutrient supply ultimately controlled whether microbes could achieve the maximum expected decomposition rate at a given temperature. Collectively, we demonstrated that exogenous nutrient supply and immobilization are critical control points for decomposition of organic matter.
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| 6. |
- Frainer, André, 1982-, et al.
(author)
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Shifts in ecosystem functioning of a detritus-based foodweb explained by imbalances between resource and consumer stoichiometry
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Other publication (other academic/artistic)abstract
- The stoichiometric imbalance between consumers and resources can affect both resource processing rates and consumer growth, and thus constitutes a potentially important driver of ecosystem functioning. We hypothesized that imbalances in nitrogen (N), phosphorus (P), and carbon (C) concentrations between detritus and detritivores would have contrasting effects on two related ecosystem processes, with stronger imbalances triggering compensatory feeding while simultaneously constraining detritivore growth. In a stream field experiment, we found that growth of detritivores was constrained by stoichiometric imbalances mostly driven by N limitation, but there was no evidence for compensatory feeding. However, when offered diets of mixed litter with varying N:P and C:N, detritivores preferred the litter species showing the closest match to their own N:P and C:N, which drove accelerated processing of the preferred species in mixture. Our results highlight the role of stoichiometric imbalances between consumers and resources in regulating ecosystem processes.
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| 7. |
- Frainer, André, et al.
(author)
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Stoichiometric imbalances between detritus and detritivores are related to shifts in ecosystem functioning
- 2016
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In: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 125:6, s. 861-871
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Journal article (peer-reviewed)abstract
- How are resource consumption and growth rates of litter-consuming detritivores affected by imbalances between consumer and litter C:N:P ratios? To address this question, we offered leaf litter as food to three aquatic detritivore species, which represent a gradient of increasing body N: P ratios: a crustacean, a caddisfly and a stonefly. The detritivores were placed in microcosms and submerged in a natural stream. Four contrasting leaf species were offered, both singly and in two-species mixtures, to obtain different levels of stoichiometric imbalance between the resources and their consumers. The results suggest that detritivore growth was constrained by N rather than C or P, even though 1) the N: P ratios of the consumers' body tissue was relatively low and 2) microbial leaf conditioning during the experiment reduced the N:P imbalance between detritivores and leaf litter. This surprisingly consistent N limitation may be a consequence of cumulative N-demand arising from the production of N-rich chitin in the exoskeletons of all three consumer species, which is lost during regular moults, in addition to N-demand for silk production by the caddisfly. These N requirements are not commonly quantified in stoichiometric analyses of arthropod consumers. There was no evidence for compensatory feeding, but when offered mixed-species litter varying in C:N:P ratios, detritivores consumed more of the litter species showing the highest N:P and lowest C:N ratio, accelerating the mass loss of the preferred leaf species in the litter mixture. These results show that imbalances in consumer-resource stoichiometry can have contrasting effects on coupled processes, highlighting a challenge in developing a mechanistic understanding of the role of stoichiometry in regulating ecosystem processes such as leaf litter decomposition.
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| 8. |
- Handa, I. Tanya, et al.
(author)
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Consequences of biodiversity loss for litter decomposition across biomes
- 2014
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 509:7499, s. 218-221
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Journal article (peer-reviewed)abstract
- The decomposition of dead organic matter is a major determinant of carbon and nutrient cycling in ecosystems, and of carbon fluxes between the biosphere and the atmosphere(1-3). Decomposition is driven by a vast diversity of organisms that are structured in complex food webs(2,4). Identifying the mechanisms underlying the effects of biodiversity on decomposition is critical(4-6) given the rapid loss of species worldwide and the effects of this loss on human well-being(7-9). Yet despite comprehensive syntheses of studies on how biodiversity affects litter decomposition(4-6,10), key questions remain, including when, where and how biodiversity has a role and whether general patterns and mechanisms occur across ecosystems and different functional types of organism(4,9-12). Here, in field experiments across five terrestrial and aquatic locations, ranging from the subarctic to the tropics, we show that reducing the functional diversity of decomposer organisms and plant litter types slowed the cycling of litter carbon and nitrogen. Moreover, we found evidence of nitrogen transfer from the litter of nitrogen-fixing plants to that of rapidly decomposing plants, but not between other plant functional types, highlighting that specific interactions in litter mixtures control carbon and nitrogen cycling during decomposition. The emergence of this general mechanism and the coherence of patterns across contrasting terrestrial and aquatic ecosystems suggest that biodiversity loss has consistent consequences for litter decomposition and the cycling of major elements on broad spatial scales.
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| 9. |
- Jabiol, Jeremy, et al.
(author)
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Diversity patterns of leaf-associated aquatic hyphomycetes along a broad latitudinal gradient
- 2013
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In: Fungal ecology. - : Elsevier. - 1754-5048 .- 1878-0083. ; 6:5, s. 439-448
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Journal article (peer-reviewed)abstract
- Information about the global distribution of aquatic hyphomycetes is scarce, despite the primary importance of these fungi in stream ecosystem functioning. In particular, the relationship between their diversity and latitude remains unclear, due to a lack of coordinated surveys across broad latitudinal ranges. This study is a first report on latitudinal patterns of aquatic hyphomycete diversity associated with native leaf-litter species in five streams located along a gradient extending from the subarctic to the tropics. Exposure of leaf litter in mesh bags of three different mesh sizes facilitated assessing the effects of including or excluding different size-classes of litter-consuming invertebrates. Aquatic hyphomycete evenness was notably constant across all sites, whereas species richness and diversity, expressed as the Hill number, reached a maximum at mid-latitudes (Mediterranean and temperate streams). These latitudinal patterns were consistent across litter species, despite a notable influence of litter identity on fungal communities at the local scale. As a result, the bell-shaped distribution of species richness and Hill diversity deviated markedly from the latitudinal patterns of most other groups of organisms. Differences in the body-size distribution of invertebrate communities colonizing the leaves had no effect on aquatic hyphomycete species richness, Hill diversity or evenness, but invertebrates could still influence fungal communities by depleting litter, an effect that was not captured by the design of our experiment. (C) 2013 Elsevier Ltd and The British Mycological Society. All rights reserved.
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| 10. |
- Nord, Helena, et al.
(author)
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Characterization of novel and complex genomic aberrations in glioblastoma using a 32K BAC array
- 2009
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In: Neuro-Oncology. - : Oxford University Press (OUP). - 1522-8517 .- 1523-5866. ; 11:6, s. 803-818
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Journal article (peer-reviewed)abstract
- Glioblastomas (GBs) are malignant CNS tumors often associated with devastating symptoms. Patients with GB have a very poor prognosis, and despite treatment, most of them die within 12 months from diagnosis. Several pathways, such as the RAS, tumor protein 53 (TP53), and phosphoinositide kinase 3 (PIK3) pathways, as well as the cell cycle control pathway, have been identified to be disrupted in this tumor. However, emerging data suggest that these aberrations represent only a fraction of the genetic changes involved in gliomagenesis. In this study, we have applied a 32K clone-based genomic array, covering 99% of the current assembly of the human genome, to the detailed genetic profiling of a set of 78 GBs. Complex patterns of aberrations, including high and narrow copy number amplicons, as well as a number of homozygously deleted loci, were identified. Amplicons that varied both in number (three on average) and in size (1.4 Mb on average) were frequently detected (81% of the samples). The loci encompassed not only previously reported oncogenes (EGFR, PDGFRA, MDM2, and CDK4) but also numerous novel oncogenes as GRB10, MKLN1, PPARGC1A, HGF, NAV3, CNTN1, SYT1, and ADAMTSL3. BNC2, PTPLAD2, and PTPRE, on the other hand, represent novel candidate tumor suppressor genes encompassed within homozygously deleted loci. Many of these genes are already linked to several forms of cancer; others represent new candidate genes that may serve as prognostic markers or even as therapeutic targets in the future. The large individual variation observed between the samples demonstrates the underlying complexity of the disease and strengthens the demand for an individualized therapy based on the genetic profile of the patient.
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| 11. |
- Salis, Romana K., et al.
(author)
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Multiple-stressor effects of dicyandiamide (DCD) and agricultural stressors on trait-based responses of stream benthic algal communities
- 2019
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In: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 693
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Journal article (peer-reviewed)abstract
- Agricultural practices often result in multiple stressors affecting stream ecosystems, and interacting stressors complicate environmental assessment and management of impacted streams. The nitrification inhibitor dicyandiamide (DCD) is used for nitrogen management on farmland. Effects of leached DCD on stream ecosystems are still largely unstudied, even though it could be relevant as a stressor on its own or in combination with other agricultural stressors. We conducted two experiments in 128 outdoor stream-fed mesocosms to assess stressor effects on biomass, cell density, taxon richness, evenness and functional trait composition of benthic algal communities. First, we examined responses to a wide DCD gradient (eight concentrations, 0–31 mg L−1) and two additional stressors, deposited fine sediment (none, high) and nutrient enrichment (ambient, enriched). Second, we determined algal responses to four stressors: DCD, sediment, nutrients, and reduced flow velocity. Here DCD treatments included controls, constant application (1.4 mg L−1) and two pulsed treatments mimicking concentration patterns in real streams (peaks 3.5 mg L−1, 2.2 mg L−1). Sediment and nutrient enrichment were influential stressors in both experiments, with fine sediment having the most pervasive effects. In Experiment 2, reduced flow velocity had pervasive effects and stressor interactions were mainly restricted to two-way interactions. DCD had few, weak stressor main effects, especially at field-realistic concentrations (Experiment 2). At the highest concentrations in Experiment 1 (above levels observed in real streams), DCD effects were still rare but some significant stressor interactions occurred. Analyses of functional traits were helpful in identifying potential mechanisms driving changes in densities and community composition. These findings suggest that, while DCD on its own may be a minor stressor, it could have adverse effects on algal communities already exposed to other stressors, a scenario common in agricultural streams.
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| 12. |
- Shumilova, Oleksandra, et al.
(author)
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Simulating rewetting events in intermittent rivers and ephemeral streams : A global analysis of leached nutrients and organic matter
- 2019
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In: Global Change Biology. - : WILEY. - 1354-1013 .- 1365-2486. ; 25:5, s. 1591-1611
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Journal article (peer-reviewed)abstract
- Climate change and human pressures are changing the global distribution and the extent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico-chemical changes (preconditioning), and periods of flow resumption, when these substrates are rewetted and release pulses of dissolved nutrients and organic matter (OM). However, there are no estimates of the amounts and quality of leached substances, nor is there information on the underlying environmental constraints operating at the global scale. We experimentally simulated, under standard laboratory conditions, rewetting of leaves, riverbed sediments, and epilithic biofilms collected during the dry phase across 205 IRES from five major climate zones. We determined the amounts and qualitative characteristics of the leached nutrients and OM, and estimated their areal fluxes from riverbeds. In addition, we evaluated the variance in leachate characteristics in relation to selected environmental variables and substrate characteristics. We found that sediments, due to their large quantities within riverbeds, contribute most to the overall flux of dissolved substances during rewetting events (56%-98%), and that flux rates distinctly differ among climate zones. Dissolved organic carbon, phenolics, and nitrate contributed most to the areal fluxes. The largest amounts of leached substances were found in the continental climate zone, coinciding with the lowest potential bioavailability of the leached OM. The opposite pattern was found in the arid zone. Environmental variables expected to be modified under climate change (i.e. potential evapotranspiration, aridity, dry period duration, land use) were correlated with the amount of leached substances, with the strongest relationship found for sediments. These results show that the role of IRES should be accounted for in global biogeochemical cycles, especially because prevalence of IRES will increase due to increasing severity of drying events.
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| 13. |
- Tiegs, Scott D., et al.
(author)
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Global patterns and drivers of ecosystem functioning in rivers and riparian zones
- 2019
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In: Science Advances. - Washington : American Association of Advancement in Science. - 2375-2548. ; 5:1
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Journal article (peer-reviewed)abstract
- River ecosystems receive and process vast quantities of terrestrial organic carbon, the fate of which depends strongly on microbial activity. Variation in and controls of processing rates, however, are poorly characterized at the global scale. In response, we used a peer-sourced research network and a highly standardized carbon processing assay to conduct a global-scale field experiment in greater than 1000 river and riparian sites. We found that Earth's biomes have distinct carbon processing signatures. Slow processing is evident across latitudes, whereas rapid rates are restricted to lower latitudes. Both the mean rate and variability decline with latitude, suggesting temperature constraints toward the poles and greater roles for other environmental drivers (e.g., nutrient loading) toward the equator. These results and data set the stage for unprecedented "next-generation biomonitoring" by establishing baselines to help quantify environmental impacts to the functioning of ecosystems at a global scale.
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