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- 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
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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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- Duncanson, Laura, et al.
(författare)
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Aboveground biomass density models for NASA's Global Ecosystem Dynamics Investigation (GEDI) lidar mission
- 2022
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Ingår i: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257 .- 1879-0704. ; 270
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Tidskriftsartikel (refereegranskat)abstract
- NASA's Global Ecosystem Dynamics Investigation (GEDI) is collecting spaceborne full waveform lidar data with a primary science goal of producing accurate estimates of forest aboveground biomass density (AGBD). This paper presents the development of the models used to create GEDI's footprint-level (~25 m) AGBD (GEDI04_A) product, including a description of the datasets used and the procedure for final model selection. The data used to fit our models are from a compilation of globally distributed spatially and temporally coincident field and airborne lidar datasets, whereby we simulated GEDI-like waveforms from airborne lidar to build a calibration database. We used this database to expand the geographic extent of past waveform lidar studies, and divided the globe into four broad strata by Plant Functional Type (PFT) and six geographic regions. GEDI's waveform-to-biomass models take the form of parametric Ordinary Least Squares (OLS) models with simulated Relative Height (RH) metrics as predictor variables. From an exhaustive set of candidate models, we selected the best input predictor variables, and data transformations for each geographic stratum in the GEDI domain to produce a set of comprehensive predictive footprint-level models. We found that model selection frequently favored combinations of RH metrics at the 98th, 90th, 50th, and 10th height above ground-level percentiles (RH98, RH90, RH50, and RH10, respectively), but that inclusion of lower RH metrics (e.g. RH10) did not markedly improve model performance. Second, forced inclusion of RH98 in all models was important and did not degrade model performance, and the best performing models were parsimonious, typically having only 1-3 predictors. Third, stratification by geographic domain (PFT, geographic region) improved model performance in comparison to global models without stratification. Fourth, for the vast majority of strata, the best performing models were fit using square root transformation of field AGBD and/or height metrics. There was considerable variability in model performance across geographic strata, and areas with sparse training data and/or high AGBD values had the poorest performance. These models are used to produce global predictions of AGBD, but will be improved in the future as more and better training data become available.
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- Cohen, Samuel I A, et al.
(författare)
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A molecular chaperone breaks the catalytic cycle that generates toxic Aβ oligomers.
- 2015
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Ingår i: Nature Structural & Molecular Biology. - : Springer Science and Business Media LLC. - 1545-9985 .- 1545-9993. ; 22:3, s. 207-213
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Tidskriftsartikel (refereegranskat)abstract
- Alzheimer's disease is an increasingly prevalent neurodegenerative disorder whose pathogenesis has been associated with aggregation of the amyloid-β peptide (Aβ42). Recent studies have revealed that once Aβ42 fibrils are generated, their surfaces effectively catalyze the formation of neurotoxic oligomers. Here we show that a molecular chaperone, a human Brichos domain, can specifically inhibit this catalytic cycle and limit human Aβ42 toxicity. We demonstrate in vitro that Brichos achieves this inhibition by binding to the surfaces of fibrils, thereby redirecting the aggregation reaction to a pathway that involves minimal formation of toxic oligomeric intermediates. We verify that this mechanism occurs in living mouse brain tissue by cytotoxicity and electrophysiology experiments. These results reveal that molecular chaperones can help maintain protein homeostasis by selectively suppressing critical microscopic steps within the complex reaction pathways responsible for the toxic effects of protein misfolding and aggregation.
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- Ellison, David, et al.
(författare)
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Trees, forests and water : Cool insights for a hot world
- 2017
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Ingår i: Global Environmental Change. - : Elsevier BV. - 0959-3780 .- 1872-9495. ; 43, s. 51-61
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Tidskriftsartikel (refereegranskat)abstract
- Forest-driven water and energy cycles are poorly integrated into regional, national, continental and global decision-making on climate change adaptation, mitigation, land use and water management. This constrains humanity's ability to protect our planet's climate and life-sustaining functions. The substantial body of research we review reveals that forest, water and energy interactions provide the foundations for carbon storage, for cooling terrestrial surfaces and for distributing water resources. Forests and trees must be recognized as prime regulators within the water, energy and carbon cycles. If these functions are ignored, planners will be unable to assess, adapt to or mitigate the impacts of changing land cover and climate. Our call to action targets a reversal of paradigms, from a carbon-centric model to one that treats the hydrologic and climate-cooling effects of trees and forests as the first order of priority. For reasons of sustainability, carbon storage must remain a secondary, though valuable, by-product. The effects of tree cover on climate at local, regional and continental scales offer benefits that demand wider recognition. The forest- and tree-centered research insights we review and analyze provide a knowledge-base for improving plans, policies and actions. Our understanding of how trees and forests influence water, energy and carbon cycles has important implications, both for the structure of planning, management and governance institutions, as well as for how trees and forests might be used to improve sustainability, adaptation and mitigation efforts.
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- Spottiswoode, C. N., et al.
(författare)
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Rediscovery of a long-lost lark reveals the conspecificity of endangered Heteromirafra populations in the Horn of Africa
- 2013
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Ingår i: Journal of Ornithology. - : Springer Science and Business Media LLC. - 0021-8375 .- 2193-7192 .- 2193-7206. ; 154:3, s. 813-825
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Tidskriftsartikel (refereegranskat)abstract
- The African lark genus Heteromirafra is thought to consist of three threatened species inhabiting mid-altitude grasslands, one in South Africa and two in the Horn of Africa. One of the latter, Archer's Lark H. archeri of Somaliland, has not been seen with certainty since 1922. We surveyed its type locality as well as a nearby area of grassland east of Jijiga in adjacent north-eastern Ethiopia, where sightings of Heteromirafra larks have recently been made. First, we used a combination of morphological and molecular evidence to show that these recent sightings refer to the same taxon as Archer's Lark. Second, we used a combination of morphological, molecular and vocal evidence to show that these populations are conspecific with the Liben (Sidamo) Lark H. sidamoensis of southern Ethiopia, but that the Horn of Africa populations are highly distinct from Rudd's Lark H. ruddi of South Africa. Third, we suggest that the extent and quality of their habitat in north-eastern Ethiopia is small and poor, and that the type locality of Archer's Lark in Somaliland has been completely transformed. Taken together, these results imply that there is a single species of Heteromirafra in the Horn of Africa (for which the scientific name H. archeri has priority, and which we suggest retains the English name Liben Lark), consisting of two tiny populations separated by 590 km of apparently unsuitable habitats. Environmental niche models suggest that there are no environmentally similar locations elsewhere within the region. Despite the discovery of a second population, the Liben Lark remains a highly threatened species in urgent need of conservation intervention to avert the extinction of both of its populations.
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