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  • 1
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    Grazing enhances belowground carbon allocation, microbial biomass, and soil carbon in a subtropical grassland (2018)
    Wiley
    Details
    Publication Date: 2018-01-28
    Description: Despite the large contribution of rangeland and pasture to global soil organic carbon (SOC) stocks, there is considerable uncertainty about the impact of large herbivore grazing on SOC, especially for understudied subtropical grazing lands. It is well known that root system inputs are the source of most grassland SOC, but the impact of grazing on partitioning of carbon allocation to root tissue production compared to fine root exudation is unclear. Given that different forms of root C have differing implications for SOC synthesis and decomposition, this represents a significant gap in knowledge. Root exudates should contribute to SOC primarily after microbial assimilation, and thus promote microbial contributions to SOC based on stabilization of microbial necromass, whereas root litter deposition contributes directly as plant-derived SOC following microbial decomposition. Here we used in situ isotope pulse-chase methodology paired with plant and soil sampling to link plant carbon allocation patterns with SOC pools in replicated long-term grazing exclosures in subtropical pasture in Florida, USA. We quantified allocation of carbon to root tissue and measured root exudation across grazed and ungrazed plots and quantified lignin phenols to assess the relative contribution of microbial versus plant products to total SOC. We found that grazing exclusion was associated with dramatically less overall belowground allocation, with lower root biomass, fine root exudates, and microbial biomass. Concurrently, grazed pasture contained greater total SOC, and a larger fraction of SOC that originated from plant tissue deposition, suggesting that larger root litter deposition under grazing promotes greater SOC. We conclude that grazing effects on SOC depend on root system biomass, a pattern that may generalize to other C4-dominated grasslands, especially in the subtropics. Improved understanding of ecological factors underlying root system biomass may be the key to forecasting SOC and optimizing grazing management to enhance SOC accumulation. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
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  • 2
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    Integrative Research on Organic Matter Cycling Across Aquatic Gradients (2021)
    Frontiers Media SA
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    Publication Date: 2022-01-31
    Description: The goal of this research topic was to motivate innovative research that blurs traditional disciplinary and geographical boundaries. As the scientific community continues to gain momentum and knowledge about how the natural world functions, it is increasingly important that we recognize the interconnected nature of earth systems and embrace the complexities of ecosystem transitions. We are pleased to present this body of work, which embodies the spirit of research spanning across the terrestrial-aquatic continuum, from mountains to the sea. Sincerely, The Editors
    Keywords: GB3-5030 ; GC1-1581 ; Q1-390 ; atmosphere ; dynamics ; ecosystem ; interface ; Carbon ; estuarine ; organic matterriver ; marine ; transition
    Language: English
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  • 3
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    Linking Optical and Chemical Properties of Dissolved Organic Matter in Natural Waters (2021)
    Frontiers Media SA
    Details
    Publication Date: 2024-04-05
    Description: A substantial increase in the number of studies using the optical properties (absorbance and fluorescence) of dissolved organic matter (DOM) as a proxy for its chemical properties in estuaries and the coastal and open ocean has occurred during the last decade. We are making progress on finding the actual chemical compounds or phenomena responsible for DOM’s optical properties. Ultrahigh resolution mass spectrometry, in particular, has made important progress in making the key connections between optics and chemistry. But serious questions remain and the last major special issue on DOM optics and chemistry occurred nearly 10 years ago. Controversies remain from the non-specific optical properties of DOM that are not linked to discrete sources, and sometimes provide conflicting information. The use of optics, which is relatively easier to employ in synoptic and high resolution sampling to determine chemistry, is a critical connection to make and can lead to major advances in our understanding of organic matter cycling in all aquatic ecosystems. The contentions and controversies raised by our poor understanding of the linkages between optics and chemistry of DOM are bottlenecks that need to be addressed and overcome.
    Keywords: QD1-999 ; GB3-5030 ; GC1-1581 ; Q1-390 ; CDOM ; dissolved organic matter ; Absorbance ; fluorescence ; biomarkers ; Stable isotopes ; Mass Spectrometry ; dissolved organic carbon ; thema EDItEUR::P Mathematics and Science::PN Chemistry
    Language: English
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  • 4
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    Paleoreconstruction of Organic Carbon Inputs to an Oxbow Lake in the Mississippi River Watershed: Effects of Dam Construction and Land-Use Change on Regional Inputs (2015)
    Wiley
    Details
    Publication Date: 2015-09-15
    Description: We use a dated sediment core from Lake Whittington (USA) in the lower Mississippi River to reconstruct linkages in the carbon cycling and fluvial sediment dynamics over the past 80 years. Organic carbon (OC) sources were characterized using bulk (δ 13 C, ramped pyrolysis-oxidation (PyrOx) 14 C, δ 15 N, and TN:C ratios) and compound-specific (lignin phenols and fatty acids, including δ 13 C and 14 C of the fatty acids) analyses. Damming of the Missouri River in the 1950s, other hydrological modifications to the river, and soil conservation measures resulted in reduced net OC export, in spite of increasing OC concentrations. Decreasing δ 13 C values coincided with increases in δ 15 N, TN:C ratios, long-chain fatty acids and lignin-phenol concentrations, suggesting increased inputs of soil-derived OC dominated by C 3 vegetation, mainly resulting from changes in farming practices and crop changes. However, PyrOx 14 C showed no discernible differences down-core in thermochemical stability, indicating a limited impact on soil OC turnover.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    High rates of organic carbon burial in fjord sediments globally (2015)
    Springer Nature
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    Publication Date: 2015-05-29
    Description: Nature Geoscience 8, 450 (2015). doi:10.1038/ngeo2421 Authors: Richard W. Smith, Thomas S. Bianchi, Mead Allison, Candida Savage & Valier Galy The deposition and long-term burial of organic carbon in marine sediments has played a key role in controlling atmospheric O2 and CO2 concentrations over the past 500 million years. Marine carbon burial represents the dominant natural mechanism of long-term organic carbon sequestration. Fjords—deep, glacially carved estuaries at high latitudes—have been hypothesized to be hotspots of organic carbon burial, because they receive high rates of organic material fluxes from the watershed. Here we compile organic carbon concentrations from 573 fjord surface sediment samples and 124 sediment cores from nearly all fjord systems globally. We use sediment organic carbon content and sediment delivery rates to calculate rates of organic carbon burial in fjord systems across the globe. We estimate that about 18 Mt of organic carbon are buried in fjord sediments each year, equivalent to 11% of annual marine carbon burial globally. Per unit area, fjord organic carbon burial rates are one hundred times as large as the global ocean average, and fjord sediments contain twice as much organic carbon as biogenous sediments underlying the upwelling regions of the ocean. We conclude that fjords may play an important role in climate regulation on glacial–interglacial timescales.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 6
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    A multi-proxy analysis of sedimentary organic carbon in the Changjiang Estuary and adjacent shelf (2015)
    Wiley
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    Publication Date: 2015-06-23
    Description: Surface sediments from the Changjiang Estuary and adjacent shelf were analyzed using a variety of bulk and molecular techniques, including grain size composition, sediment surface area (SSA), elemental composition (C, N), stable carbon isotopic composition (δ 13 C), n -alkanes, lignin phenols, and glycerol dialkyl glycerol tetraether lipids (GDGTs), to obtain a more comprehensive understanding of the sources and fate of sedimentary organic carbon (SOC) in this dynamic region. Bulk N/C ratios of 0.09 to 0.15, δ 13 C of −24.4 ‰ to −21.1 ‰, branched/isoprenoid tetraether (BIT) index of 0 to 0.74, n -alkane content of 0.02 to 0.37 mg g −1 OC and lignin content (Λ 8 ) of 0.10 to 1.46 mg/100 mg OC and other related molecular indices in these samples indicate a mixed source of marine, soil and terrestrial plant derived OC in the study area. A three end-member mixing model using principal component analysis (PCA) factors as source markers and based on Monte-Carlo (MC) simulation was constructed to estimate the relative contributions of OC from different sources. Compared with traditional mixing models, commonly based on a few variables, this newly-developed PCA-MC model supported bulk and biomarker data and yielded a higher resolution OC inputs to different sub-regions of this system. In particular, the results showed that the average contributions of marine, soil and terrestrial OC in the study area were 35.3 %, 47.0 % and 17.6 %, and the highest contribution from each OC source was mainly observed in the shelf, inner estuary, and coastal region, respectively.
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Positive Priming of Terrestrially-Derived Dissolved Organic Matter in a Freshwater Microcosm System (2015)
    Wiley
    Details
    Publication Date: 2015-06-27
    Description: The role of priming processes in the remineralization of terrestrially-derived dissolved organic carbon (TDOC) in aquatic systems has been overlooked. We provide evidence for TDOC priming using a lab-based microcosm experiment in which TDOC was primed by the addition of 13 C-labelled algal dissolved organic carbon (ADOC) or a 13 C-labelled disaccharide (trehalose). The rate of TDOC remineralization to carbon dioxide (CO 2 ) occurred 4.1 ± 0.9 and 1.5 ± 0.3 times more rapidly with the addition of trehalose and ADOC, respectively, relative to experiments with TDOC as the sole carbon source over the course of a 301 hour incubation period. Results from these controlled experiments provide fundamental evidence for the occurrence of priming of TDOC by ADOC and a simple disaccharide. We suggest that priming effects on TDOC should be considered in carbon budgets for large-river deltas, estuaries, lakes, hydroelectric reservoirs, and continental shelves.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    An exact limit of the Aharony-Bergman-Jafferis-Maldacena theory (2016)
    American Physical Society (APS)
    Details
    Publication Date: 2016-08-24
    Description: Author(s): Marco S. Bianchi and Matias Leoni We study planar Aharony-Bergman-Jafferis-Maldacena (ABJM) theory in a limit where one coupling is negligible compared to the other. We provide a recipe for exactly solving the expectation value of bosonic Bogomol’nyi-Prasad-Sommerfield (BPS) Wilson loops on arbitrary smooth contours, or the leading … [Phys. Rev. D 94, 045011] Published Tue Aug 23, 2016
    Keywords: Formal aspects of field theory, field theory in curved space
    Print ISSN: 0556-2821
    Electronic ISSN: 1089-4918
    Topics: Physics
    Published by American Physical Society (APS)
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  • 9
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    Polar features in the flagellar propulsion of E. coli bacteria (2015)
    American Physical Society (APS)
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    Publication Date: 2015-06-11
    Description: Author(s): S. Bianchi, F. Saglimbeni, A. Lepore, and R. Di Leonardo E. coli bacteria swim following a run and tumble pattern. In the run state all flagella join in a single helical bundle that propels the cell body along approximately straight paths. When one or more flagellar motors reverse direction the bundle unwinds and the cell randomizes its orientation. This ... [Phys. Rev. E 91, 062705] Published Tue Jun 09, 2015
    Keywords: Biological Physics
    Print ISSN: 1539-3755
    Electronic ISSN: 1550-2376
    Topics: Physics
    Published by American Physical Society (APS)
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  • 10
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    Historical changes in terrestrially derived organic carbon inputs to Louisiana continental margin sediments over the past 150 years (2011)
    Wiley
    Details
    Publication Date: 2011-02-10
    Description: Major rivers (and associated deltaic environments) provide the dominant pathway for the input of terrestrial-derived organic carbon in sediments (TOCT) to the ocean. Natural watershed processes and land-use changes are important in dictating the amount and character of carbon being buried on continental margins. Seven core sites were occupied on the Louisiana continental margin aboard the R/V Pelican in July 2003 along two major sediment transport pathways south and west of the Mississippi River mouth. Lignin profiles in these age-dated cores (210Pb geochronology) indicate artificial reservoir retention as a primary control on organic carbon quantity and quality reaching the margin post-1950, whereas pre-1950 sediments may reflect soil erosion due to land clearing and farming practices. Lignin (Λ8) concentrations (range 0.2 to 1.7) also indicate that TOCT delivery rates/decay processes have probably remained relatively consistent from proximal to distal stations along transects. The down-core profile at the Canyon station seems to be temporally linked and connected to inner shelf deposition, suggestive of rapid cross-shelf transport. Sources of terrestrially derived organic carbon were reflective of mixed angiosperms over the last 150 years in cores west and south of the Mississippi River delta. The lignin-phenol vegetation index (LPVI) (range 130.0 to 510) proved to be a sensitive indicator of source changes in these sediments and eliminated some of the variability compared to C/V (range 0.01 to 0.4) and S/V (range 0.9 to 2.1) ratios. Stochastic events such as hurricanes and large river floods have a measurable, albeit ephemeral, effect on the shelf TOCT record. Burial of TOCT on the river-dominated Louisiana continental margin is largely driven by anthropogenic land-use alterations in the last 150 years. Land-use changes in the Mississippi River basin and river damming have likely affected carbon cycling and TOCT burial on the Louisiana continental margin over a large spatial extent as observed by similar trends in cores from across and along the margin.
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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