| 1. |
- Salles, J, et al.
(författare)
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Vitamin D status modulates mitochondrial oxidative capacities in skeletal muscle: role in sarcopenia
- 2022
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Ingår i: Communications biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 5:1, s. 1288-
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Tidskriftsartikel (refereegranskat)abstract
- Skeletal muscle mitochondrial function is the biggest component of whole-body energy output. Mitochondrial energy production during exercise is impaired in vitamin D-deficient subjects. In cultured myotubes, loss of vitamin D receptor (VDR) function decreases mitochondrial respiration rate and ATP production from oxidative phosphorylation. We aimed to examine the effects of vitamin D deficiency and supplementation on whole-body energy expenditure and muscle mitochondrial function in old rats, old mice, and human subjects. To gain further insight into the mechanisms involved, we used C2C12 and human muscle cells and transgenic mice with muscle-specific VDR tamoxifen-inducible deficiency. We observed that in vivo and in vitro vitamin D fluctuations changed mitochondrial biogenesis and oxidative activity in skeletal muscle. Vitamin D supplementation initiated in older people improved muscle mass and strength. We hypothesize that vitamin D supplementation is likely to help prevent not only sarcopenia but also sarcopenic obesity in vitamin D-deficient subjects.
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| 2. |
- Aho, Kelly S., et al.
(författare)
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Distinct concentration-discharge dynamics in temperate streams and rivers : CO2 exhibits chemostasis while CH4 exhibits source limitation due to temperature control
- 2021
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Ingår i: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 66:10, s. 3656-3668
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Tidskriftsartikel (refereegranskat)abstract
- Streams and rivers are significant sources of carbon dioxide (CO2) and methane (CH4) to the atmosphere. However, the magnitudes of these fluxes are uncertain, in part, because dissolved greenhouse gases (GHGs) can exhibit high spatiotemporal variability. Concentration-discharge (C-Q) relationships are commonly used to describe temporal variability stemming from hydrologic controls on solute production and transport. This study assesses how the partial pressures of two GHGs—pCO2 and pCH4—vary across hydrologic conditions over 4 yr in eight nested streams and rivers, at both annual and seasonal timescales. Overall, the range of pCO2 was constrained, ranging from undersaturated to nine times oversaturated, while pCH4 was highly variable, ranging from 3 to 500 times oversaturated. We show that pCO2 exhibited chemostatic behavior (i.e., no change with Q), in part, due to carbonate buffering and seasonally specific storm responses. In contrast, we show that pCH4 generally exhibited source limitation (i.e., a negative relationship with Q), which we attribute to temperature-mediated production. However, pCH4 exhibited chemostasis in a wetland-draining stream, likely due to hydrologic connection to the CH4-rich wetland. These findings have implications for CO2 and CH4 fluxes, which are controlled by concentrations and gas transfer velocities. At high Q, enhanced gas transfer velocity acts on a relatively constant CO2 stock but on a diminishing CH4 stock. In other words, CO2 fluxes increase with Q, while CH4 fluxes are modulated by the divergent Q dynamics of gas transfer velocity and concentration.
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| 3. |
- Gomez-Gener, L., et al.
(författare)
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Global carbon dioxide efflux from rivers enhanced by high nocturnal emissions
- 2021
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 14, s. 289-294
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Tidskriftsartikel (refereegranskat)abstract
- Carbon dioxide (CO2) emissions to the atmosphere from running waters are estimated to be four times greater than the total carbon (C) flux to the oceans. However, these fluxes remain poorly constrained because of substantial spatial and temporal variability in dissolved CO2 concentrations. Using a global compilation of high-frequency CO2 measurements, we demonstrate that nocturnal CO2 emissions are on average 27% (0.9 gC m(-2) d(-1)) greater than those estimated from diurnal concentrations alone. Constraints on light availability due to canopy shading or water colour are the principal controls on observed diel (24 hour) variation, suggesting this nocturnal increase arises from daytime fixation of CO2 by photosynthesis. Because current global estimates of CO2 emissions to the atmosphere from running waters (0.65-1.8 PgC yr(-1)) rely primarily on discrete measurements of dissolved CO2 obtained during the day, they substantially underestimate the magnitude of this flux. Accounting for night-time CO2 emissions may elevate global estimates from running waters to the atmosphere by 0.20-0.55 PgC yr(-1). Failing to account for emission differences between day and night will lead to an underestimate of global CO2 emissions from rivers by up to 0.55 PgC yr(-1), according to analyses of high-frequency CO2 measurements.
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| 4. |
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| 6. |
- Rocher-Ros, Gerard, et al.
(författare)
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Global methane emissions from rivers and streams
- 2023
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Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 621:7979, s. 530-535
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Tidskriftsartikel (refereegranskat)abstract
- Methane (CH4) is a potent greenhouse gas and its concentrations have tripled in the atmosphere since the industrial revolution. There is evidence that global warming has increased CH4 emissions from freshwater ecosystems 1,2, providing positive feedback to the global climate. Yet for rivers and streams, the controls and the magnitude of CH4 emissions remain highly uncertain 3,4. Here we report a spatially explicit global estimate of CH4 emissions from running waters, accounting for 27.9 (16.7–39.7) Tg CH4 per year and roughly equal in magnitude to those of other freshwater systems 5,6. Riverine CH4 emissions are not strongly temperature dependent, with low average activation energy (EM = 0.14 eV) compared with that of lakes and wetlands (EM = 0.96 eV) 1. By contrast, global patterns of emissions are characterized by large fluxes in high- and low-latitude settings as well as in human-dominated environments. These patterns are explained by edaphic and climate features that are linked to anoxia in and near fluvial habitats, including a high supply of organic matter and water saturation in hydrologically connected soils. Our results highlight the importance of land–water connections in regulating CH4 supply to running waters, which is vulnerable not only to direct human modifications but also to several climate change responses on land.
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| 7. |
- Stanley, Emily H., et al.
(författare)
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GRiMeDB : the global river methane database of concentrations and fluxes
- 2023
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Ingår i: Earth System Science Data. - : Copernicus Publications. - 1866-3508 .- 1866-3516. ; 15:7, s. 2879-2926
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Tidskriftsartikel (refereegranskat)abstract
- Despite their small spatial extent, fluvial ecosystems play a significant role in processing and transporting carbon in aquatic networks, which results in substantial emission of methane (CH4) into the atmosphere. For this reason, considerable effort has been put into identifying patterns and drivers of CH4 concentrations in streams and rivers and estimating fluxes to the atmosphere across broad spatial scales. However, progress toward these ends has been slow because of pronounced spatial and temporal variability of lotic CH4 concentrations and fluxes and by limited data availability across diverse habitats and physicochemical conditions. To address these challenges, we present a comprehensive database of CH4 concentrations and fluxes for fluvial ecosystems along with broadly relevant and concurrent physical and chemical data. The Global River Methane Database (GriMeDB; 10.6073/pasta/f48cdb77282598052349e969920356ef, Stanley et al., 2023) includes 24ĝ€¯024 records of CH4 concentration and 8205 flux measurements from 5029 unique sites derived from publications, reports, data repositories, unpublished data sets, and other outlets that became available between 1973 and 2021. Flux observations are reported as diffusive, ebullitive, and total CH4 fluxes, and GriMeDB also includes 17ĝ€¯655 and 8409 concurrent measurements of concentrations and 4444 and 1521 fluxes for carbon dioxide (CO2) and nitrous oxide (N2O), respectively. Most observations are date-specific (i.e., not site averages), and many are supported by data for 1 or more of 12 physicochemical variables and 6 site variables. Site variables include codes to characterize marginal channel types (e.g., springs, ditches) and/or the presence of human disturbance (e.g., point source inputs, upstream dams). Overall, observations in GRiMeDB encompass the broad range of the climatic, biological, and physical conditions that occur among world river basins, although some geographic gaps remain (arid regions, tropical regions, high-latitude and high-altitude systems). The global median CH4 concentration (0.20ĝ€¯μmolL-1) and diffusive flux (0.44ĝ€¯mmolm-2d-1) in GRiMeDB are lower than estimates from prior site-averaged compilations, although ranges (0 to 456ĝ€¯μmolL-1 and -136 to 4057ĝ€¯mmolm-2d-1) and standard deviations (10.69 and 86.4) are greater for this larger and more temporally resolved database. Available flux data are dominated by diffusive measurements despite the recognized importance of ebullitive and plant-mediated CH4 fluxes. Nonetheless, GriMeDB provides a comprehensive and cohesive resource for examining relationships between CH4 and environmental drivers, estimating the contribution of fluvial ecosystems to CH4 emissions, and contextualizing site-based investigations.
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