| 1. |
- Berggren, Martin, et al.
(författare)
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Unified understanding of intrinsic and extrinsic controls of dissolved organic carbon reactivity in aquatic ecosystems
- 2022
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 103:9
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Tidskriftsartikel (refereegranskat)abstract
- Despite our growing understanding of the global carbon cycle, scientific consensus on the drivers and mechanisms that control dissolved organic carbon (DOC) turnover in aquatic systems is lacking, hampered by the mismatch between research that approaches DOC reactivity from either intrinsic (inherent chemical properties) or extrinsic (environmental context) perspectives. Here we propose a conceptual view of DOC reactivity in which the combination of intrinsic and extrinsic factors controls turnover rates and determines which reactions will occur. We review three major types of reactions (biological, photochemical, and flocculation) from an intrinsic chemical perspective and further define the environmental features that modulate the expression of chemically inherent reactivity potential. Finally, we propose hypotheses of how extrinsic and intrinsic factors together shape patterns in DOC turnover across the land-to-ocean continuum, underscoring that there is no intrinsic DOC reactivity without environmental context. By acknowledging the intrinsic–extrinsic control duality, our framework intends to foster improved modeling of DOC reactivity and its impact on ecosystem services.
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| 2. |
- Lapierre, Jean-Francois, et al.
(författare)
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Increases in terrestrially derived carbon stimulate organic carbon processing and CO2 emissions in boreal aquatic ecosystems
- 2013
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- The concentrations of terrestrially derived dissolved organic carbon have been increasing throughout northern aquatic ecosystems in recent decades, but whether these shifts have an impact on aquatic carbon emissions at the continental scale depends on the potential for this terrestrial carbon to be converted into carbon dioxide. Here, via the analysis of hundreds of boreal lakes, rivers and wetlands in Canada, we show that, contrary to conventional assumptions, the proportion of biologically degradable dissolved organic carbon remains constant and the photochemical degradability increases with terrestrial influence. Thus, degradation potential increases with increasing amounts of terrestrial carbon. Our results provide empirical evidence of a strong causal link between dissolved organic carbon concentrations and aquatic fluxes of carbon dioxide, mediated by the degradation of land-derived organic carbon in aquatic ecosystems. Future shifts in the patterns of terrestrial dissolved organic carbon in inland waters thus have the potential to significantly increase aquatic carbon emissions across northern landscapes.
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| 3. |
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| 4. |
- Panneer Selvam, Balathandayuthabani, et al.
(författare)
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Degradation potentials of dissolved organic carbon (DOC) from thawed permafrost peat
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Global warming can substantially affect the export of dissolved organic carbon (DOC) from peat-permafrost to aquatic systems. The direct degradability of such peat-derived DOC, however, is poorly constrained because previous permafrost thaw studies have mainly addressed mineral soil catchments or DOC pools that have already been processed in surface waters. We incubated peat cores from a palsa mire to compare an active layer and an experimentally thawed permafrost layer with regard to DOC composition and degradation potentials of pore water DOC. Our results show that DOC from the thawed permafrost layer had high initial degradation potentials compared with DOC from the active layer. In fact, the DOC that showed the highest bio- and photo-degradability, respectively, originated in the thawed permafrost layer. Our study sheds new light on the DOC composition of peat-permafrost directly upon thaw and suggests that past estimates of carbon-dioxide emissions from thawed peat permafrost may be biased as they have overlooked the initial mineralization potential of the exported DOC.
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| 5. |
- Panneer Selvam, Balathandayuthabani, et al.
(författare)
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Effect of permafrost thaw on labile dissolved organic carbon in a northern palsa mire
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Permafrost thaw can substantially increase the total export of dissolved organic carbon (DOC) to aquatic systems. The effects for bio- and photo-degradable DOC, however, are poorly known, because previous studies have mainly targeted lakes and streams which are indirectly affected by permafrost, while direct experimental work on permafrost thaw is lacking. We thus incubated permafrost cores from a northern palsa mire in a climate chamber to directly compare active layer and the effect of thaw on 1) DOC composition (using fluorescence analyses and PARAFAC modeling) and 2) DOC bioavailability and photo-degradability. Our results show that compared with DOC from the active layer, the permafrost-thaw DOC was more bioavailable, coherent with its optical characteristics indicating higher protein content and lower molecular weight DOC. This biolabile DOC, however, does not appear to contribute to photo-oxidation as we found no difference in photo-degradation between the active layer and permafrost DOC. Our study suggests that permafrost thaw results in the export of both bio- and photo-degradable DOC, indicating that an increase in permafrost thaw could positively affect the carbon cycling of aquatic ecosystems.
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| 6. |
- Berggren, Martin, et al.
(författare)
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Systematic microbial production of optically active dissolved organic matter in subarctic lake water
- 2020
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Ingår i: Limnology and Oceanography. - : Association for the Sciences of Limnology and Oceanography (ASLO). - 0024-3590 .- 1939-5590. ; 65:5
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Tidskriftsartikel (refereegranskat)abstract
- The ecology and biogeochemistry of lakes in the subarctic region are particularly sensitive to changes in the abundance and optical properties of dissolved organic matter (DOM). External input of colored DOM to these lakes is an extensively researched topic, but little is known about potential reciprocal feedbacks between the optical properties of DOM and internal microbial processes in the water. We performed 28-day dark laboratory incubation trials on water from 101 subarctic tundra lakes in northern Sweden, measuring the microbial decay of DOM and the resulting dynamics in colored (CDOM) and fluorescent (FDOM) DOM components. While losses in dissolved oxygen during the incubations corresponded to a 20% decrease in mean DOM, conversely the mean CDOM and total FDOM increased by 22% and 30%, respectively. However, the patterns in microbial transformation of the DOM were not the same in all lakes. Notably, along the gradient of increasing ambient CDOM (water brownness), the lakes showed decreased microbial production of protein-like fluorescence, lowered DOM turnover rates and decreasing bacterial growth per unit of DOM. These trends indicate that browning of subarctic lakes systematically change the way that bacteria interact with the ambient DOM pool. Our study underscores that there is no unidirectional causal link between microbial processes and DOM optical properties, but rather reciprocal dependence between the two.
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| 7. |
- Goncalves dos Santos, Karen Cristine, et al.
(författare)
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Unrelated Fungal Rust Candidate Effectors Act on Overlapping Plant Functions
- 2021
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Ingår i: Microorganisms. - : MDPI. - 2076-2607. ; 9:5
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Tidskriftsartikel (refereegranskat)abstract
- Rust fungi cause epidemics that threaten the production of important plant species, such as wheat and soy. Melampsora larici-populina (Mlp) causes the poplar rust and encodes at least 1184 candidate effectors (CEs) whose functions are poorly known. In this study, we sequenced the transcriptome and used mass spectrometry to analyze the metabolome of Arabidopsis plants constitutively expressing 14 Mlp CEs and of a control line to discover alterations leading to plant susceptibility. We found 2299 deregulated genes across the experiment. Genes involved in pattern-triggered immunity, such as FRK1, PR1, RBOHD, and WRKY33, as well as AUX/IAA genes were down-regulated. We further observed that 680 metabolites were deregulated in at least one CE-expressing transgenic line, with “highly unsaturated and phenolic compounds” and “peptides” enriched among down- and up-regulated metabolites. Interestingly, transgenic lines expressing unrelated CEs had correlated patterns of gene and metabolite deregulation, while expression of CEs belonging to the same family deregulated different genes and metabolites. Thus, our results uncouple effector sequence similarity and function. This supports that effector functional investigation in the context of their virulence activity and effect on plant susceptibility requires the investigation of the individual effector and precludes generalization based on sequence similarity.
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| 8. |
- Guillemette, Francois, et al.
(författare)
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Preferential sequestration of terrestrial organic matter in boreal lake sediments
- 2017
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Ingår i: Journal of Geophysical Research - Biogeosciences. - : AMER GEOPHYSICAL UNION. - 2169-8953 .- 2169-8961. ; 122:4, s. 863-874
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Tidskriftsartikel (refereegranskat)abstract
- The molecular composition and origin has recently been demonstrated to play a critical role in the persistence of organic matter in lake water, but it is unclear to what degree chemical attributes and sources may also control settling and burial of organic matter in lake sediments. Here we compared the annual contribution of allochthonous and autochthonous sources to the organic matter settling in the water column and present in the sediments of 12 boreal lakes. We used the fluorescence properties and elemental composition of the organic matter to trace its origin and found a consistent pattern of increasing contribution of terrestrial compounds in the sediments as compared to the settling matter, with an annual average allochthony of similar to 87% and similar to 57%, respectively. Seasonal data revealed a predominance of in-lake-produced compounds sinking in the water column in summer. Yet only a slight concurrent decrease in the contribution of terrestrial C to lake sediments was observed during the same period, and sediment allochthony increased again to high levels in autumn. Our results reveal a preferential preservation of allochthonous matter in the sediments and highlight the role of lakes as sequesters of organic carbon primarily originating from the surrounding landscape.
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| 9. |
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| 10. |
- Guillemette, Francois, et al.
(författare)
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Unraveling the size-dependent optical properties of dissolved organic matter
- 2018
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 63:2, s. 588-601
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Tidskriftsartikel (refereegranskat)abstract
- The size‐dependent optical properties of dissolved organic matter (DOM) from four Swedish lakes were investigated using High Performance Size Exclusion Chromatography (HPSEC) in conjunction with online characterization of absorbance (240–600 nm) and fluorescence (excitation: 275 nm, emission: 300–600 nm). The molecular size of chromophoric DOM (CDOM) was consistently higher than that of fluorescent DOM (FDOM), with an average difference of 0.37 kDa. The relative abundance of FDOM vs. CDOM ranged from 0.3 to 0.7 across lakes, and increased with decreasing average molecular size. Across sites, the CDOM spectral slopes of the large molecular size fraction were highly similar while the low molecular size fraction differed and contributed to different bulk spectral slopes. Our results indicate structural congruence of high molecular size DOM across systems while lake trophic status determined the characteristics of the low size range. Furthermore, the combination of HPSEC and parallel factor analysis (HPSEC‐PARAFAC2) allowed the decomposition of DOM fluorescence chromatograms. Three humic‐like components and one protein‐like component with broadly overlapping molecular size distributions were identified. This overlap provides further evidence for the supramolecular assembly hypothesis since fluorophores, as revealed by PARAFAC2, occur in aggregates of overlapping molecular size. Our results further suggest a link between the molecular size of these fluorophores and the associated supramolecular assemblies. This study demonstrates the potential for HPSEC and novel mathematical approaches to provide unprecedented insights into the relationship between optical and chemical properties of DOM in aquatic systems.
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| 11. |
- Hensgens, Geert, et al.
(författare)
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Impacts of litter decay on organic leachate composition and reactivity
- 2021
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 154:1, s. 99-117
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Tidskriftsartikel (refereegranskat)abstract
- Litter decomposition produces labile and recalcitrant forms of dissolved organic matter (DOM) that significantly affect soil carbon (C) sequestration. Chemical analysis of this DOM can provide important knowledge for understanding soil DOM dynamics, but detailed molecular analyses on litter derived DOM are scarce. Here we use ultrahigh resolution mass spectrometry (FT-ICR MS) to characterize the molecular composition of DOM from fresh and progressively decomposed litter samples. We compared high reactive (HR) and low reactive (LR) litter sources with regard to changes in the chemistry and bioavailability of leachates throughout the early phase of litter decay. We show that litter reactivity is a driver of chemical changes in the leached DOM of litter species. Birch, alder and Vaccinium (i.e. HR) litter initially produced more DOM with a higher lability than that of spruce, pine and wood (i.e. LR) litter. Labile oxidized phenolic compounds were abundant in leachates produced during the initial HR litter decay stages, indicating litter lignin degradation. However, the similarity in chemistry between HR and LR leachates increased during the litter decay process as highly leachable structures in HR litter were depleted. In contrast, chemistry of leachates from LR litter changed little during the litter decay process. The oxygenated phenolic compounds from HR litter were driving the lability of HR leachates and the changes in relative abundance of molecules during DOM incubation. This appeared to result in the creation of stable aliphatic secondary microbial compounds. In LR leachates, lability was driven by labile aliphatic compounds, while more resistant phenolic compounds were associated with recalcitrance. These results show how DOM dynamics follow different paths depending on litter reactivity, which has important implications for soil biogeochemistry and C sequestration.
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| 12. |
- Lebret, Karen, et al.
(författare)
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High abundances of the nuisance raphidophyte Gonyostomum semen in brown water lakes are associated with high concentrations of iron
- 2018
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Algal blooms occur frequently in lakes and oceans and the causes and consequences of those are often studied. In this study, we focus on a less well known type of algal bloom by the freshwater raphidophyte Gonyostomum semen. This species' abundance and occurrence is increasing, especially in brown water lakes, the most abundant lake type in the boreal zone. The aim of the study was to investigate which environmental factors are associated with G. semen by statistical evaluation of field data of 95 Swedish lakes over five years. Although we found G. semen to be associated with dark waters it was, contrary to our expectations, mainly high concentrations of iron, and only to a lesser extent high TOC (total organic carbon) concentrations, that were associated with blooms of G. semen. In addition, high phosphorus concentrations and low pH also appear to facilitate G. semen blooms. We suggest that browning of lakes caused by increased iron concentrations may decrease net heterotrophy by fostering heavy algal blooms, i.e. the opposite to commonly assumed effects of increased DOM (dissolved organic matter).
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| 13. |
- Mostovaya, Alina, et al.
(författare)
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Effects of compositional changes on reactivity continuum and decomposition kinetics of lake dissolved organic matter
- 2016
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 121:7, s. 1733-1746
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Tidskriftsartikel (refereegranskat)abstract
- To address the link between the composition and decomposition of freshwater dissolved organic matter (DOM), we manipulated the DOM from three boreal lakes using preincubations with UV light to cleave large aromatic molecules and polyvinylpyrrolidone (PVP) to remove colored phenolic compounds. Subsequently, we monitored the dissolved organic carbon (DOC) loss over 4months of microbial degradation in the dark to assess how compositional changes in DOM affected different aspects of the reactivity continuum, including the distribution of the apparent decay coefficients. We observed profound effects on decomposition kinetics, with pronounced shifts in the relative share of rapidly and more slowly decomposing fractions of the DOM. In the UV-exposed treatment initial apparent decay coefficient k(0) was almost threefold higher than in the control. Significantly higher relative DOC loss in the UV-exposed treatment was sustained for 2months of incubation, after which decay coefficients converged with those in the control. The PVP removed compounds with absorbance and fluorescence characteristics representative of aromatic compounds, which led to slower decomposition, compared to that in the control. Our results demonstrate the reactivity continuum underlying the decomposition of DOM in freshwaters and highlight the importance of intrinsic properties of DOM in determining its decomposition kinetics.
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| 14. |
- Panneer Selvam, Balathandayuthabani, et al.
(författare)
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Influence of soil frost on the character and degradability of dissolved organic carbon in boreal forest soils
- 2016
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8961 .- 2169-8953. ; 121:3, s. 829-840
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies suggest that increases in extent and duration of winter soil frost increases dissolved organic carbon (DOC) concentrations in boreal riparian soils and connected aquatic systems during the subsequent spring and summer. However, little is known about the impact of frost on DOC character and its degradability. We applied three experimental treatments to riparian soils in northern Sweden—shallow soil frost (insulated), deep soil frost (snow removed) and control plots—to test the effect of different soil frost regimes on the chemical characteristics and degradability of soil DOC. Soil pore water samples were analyzed using excitation-emission fluorescence (parallel factor analysis) combined with biological and photochemical degradation experiments. We found that the absolute bacterial metabolic rates were significantly lower in samples from the shallow soil frost treatments, compared with the other treatments. Explorative multivariate analyses indicate that increasing soil frost is contributing to increased protein-like fluorescence and to increased biological degradability of the DOC. Our study shows that decreases in riparian soil frost due to climate warming may not only contribute to decreased riparian DOC concentrations but also lead to shifts in the DOC composition, resulting in decreased biodegradability (yet similar photodegradability) of the DOC that is exported from riparian soils to streams.
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| 15. |
- Raverdy, Violeta, et al.
(författare)
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Performance of non-invasive tests for liver fibrosis and resolution after bariatric surgery.
- 2024
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Ingår i: Metabolism: clinical and experimental. - 1532-8600. ; 153
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Tidskriftsartikel (refereegranskat)abstract
- The value of non-invasive tests for monitoring the resolution of significant liver fibrosis after treatment is poorly investigated. We compared the performances of six non-invasive tests to predict the resolution of significant fibrosis after bariatric surgery.Participants were individuals with obesity submitted to needle liver biopsy at the time of bariatric surgery, and 12 and/or 60months after surgery. We calculated the fibrosis-4 index (FIB-4), NAFLD fibrosis score (NFS), AST to platelet ratio index (APRI), Hepatic fibrosis score (HFS), Fibrosis NAFLD index (FNI), and Liver risk score (LRS) at each time point, and compared their performances for predicting significant fibrosis (F≥2) and its resolution following surgery.At baseline, 2436 patients had liver biopsy, including 261 (10.7%) with significant fibrosis. Overall, 672 patients had pre- and post-operative biopsies (564 at M12 and 328 at M60). The fibrosis stage decreased at M12 and M60 (p<0.001 vs M0). Resolution of significant fibrosis occurred in 58/121 (47.9%) at M12 and 32/50 (64%) at M60. The mean value of all tests decreased after surgery, except for FIB-4. Performances for predicting fibrosis resolution was higher at M60 than at M12 for all tests, and maximal at M60 for FNI and LRS: area under the curve 0.843 (95%CI 0.71-0.95) and 0.92 (95%CI 0.84-1.00); positive likelihood ratio 3.75 (95% CI 1.33-10.59) and 4.58 (95% CI 1.65-12.70), respectively.Results showed the value and limits of non-invasive tests for monitoring the evolution of liver fibrosis after an intervention. Following bariatric surgery, the best performances to predict the resolution of significant fibrosis were observed at M60 with tests combining liver and metabolic traits, namely FNI and LRS.
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