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- Luo, Y. -W, et al.
(author)
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Database of diazotrophs in global ocean : abundance, biomass and nitrogen fixation rates
- 2012
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In: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 4:1, s. 47-73
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Journal article (peer-reviewed)abstract
- Marine N-2 fixing microorganisms, termed di-azotrophs, are a key functional group in marine pelagic ecosystems. The biological fixation of dinitrogen ( N-2) to bioavailable nitrogen provides an important new source of nitrogen for pelagic marine ecosystems and influences primary productivity and organic matter export to the deep ocean. As one of a series of efforts to collect biomass and rates specific to different phytoplankton functional groups, we have constructed a database on diazotrophic organisms in the global pelagic upper ocean by compiling about 12 000 direct field measurements of cyanobacterial diazotroph abundances (based on microscopic cell counts or qPCR assays targeting the nifH genes) and N-2 fixation rates. Biomass conversion factors are estimated based on cell sizes to convert abundance data to diazotrophic biomass. The database is limited spatially, lacking large regions of the ocean especially in the Indian Ocean. The data are approximately log-normal distributed, and large variances exist in most sub-databases with non-zero values differing 5 to 8 orders of magnitude. Reporting the geometric mean and the range of one geometric standard error below and above the geometric mean, the pelagic N-2 fixation rate in the global ocean is estimated to be 62 (52-73) Tg Nyr(-1) and the pelagic diazotrophic biomass in the global ocean is estimated to be 2.1 (1.4-3.1) Tg C from cell counts and to 89 (43-150) Tg C from nifH- based abundances. Reporting the arithmetic mean and one standard error instead, these three global estimates are 140 +/- 9.2 Tg Nyr(-1), 18 +/- 1.8 Tg C and 590 +/- 70 Tg C, respectively. Uncertainties related to biomass conversion factors can change the estimate of geometric mean pelagic diazotrophic biomass in the global ocean by about +/- 70 %. It was recently established that the most commonly applied method used to measure N-2 fixation has underestimated the true rates. As a result, one can expect that future rate measurements will shift the mean N-2 fixation rate upward and may result in significantly higher estimates for the global N-2 fixation. The evolving database can nevertheless be used to study spatial and temporal distributions and variations of marine N-2 fixation, to validate geochemical estimates and to parameterize and validate biogeochemical models, keeping in mind that future rate measurements may rise in the future.
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| 2. |
- McGillicuddy, F. C., et al.
(author)
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Novel "plum pudding" as potential drug-eluting stent coatings : Controlled release of fluvastatin
- 2006
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In: Journal of Biomedical Materials Research. Part A. - : Wiley. - 1552-4965 .- 1549-3296. ; 79A:4, s. 923-933
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Journal article (peer-reviewed)abstract
- This study evaluated novel structural motifs known as "plum pudding" gels as potential drug-eluting stent coatings. Controlled delivery of a HMG-CoA reductase inhibitor (statin) from the intravascular stent surface represents a potential therapeutic modality for prevention of in-stent restenosis (ISR). In this study, gels were comprised of fluvastatin-loaded thermoresponsive microgel particles containing the relatively hydrophilic N-isopropyl-acrylamide (NiPAAm), mixed with the more hydrophobic N-tert-butylacrylamide (NtBAAm) in different wt/wt ratios: 85/15, 65/35, and 50/50, randomly dispersed in a 65/35 or 85/15 NiPAAm/NtBAAm copolymer matrix. Fluvastatin release from 5 mu m copolymer films was greatest from the most hydrophilic systems and least from the more hydrophobic systems. Release from hydrophobic matrices appeared to be via Fickian diffusion, enabling use of the Stokes-Einstein equation to determine diffusion coefficients. Release from hydrophilic matrices was nonFickian. Fluted drug retained its bioactivity, assessed as selective inhibition of human coronary artery smooth muscle cell proliferation. When stainless steel stent wires were coated (25 mu m thickness) with fluvastatin-loaded 65/35 microgels in an 85/15 copolymer matrix, drug elution into static and perfused flow environments followed similar elution profiles. In contrast to elution from copolymer films cast on flat surfaces, diffusion from stent wires coated with hydrophilic and hydrophobic systems both followed Fickian patterns, with slightly larger diffusion coefficients for elution from the flow system. We conclude that manipulation of the relative hydrophobicities of both microgel and matrix components of "plum pudding" gels results in tightly regulated release of fluvastatin over an extended time period relevant to initiation and propagation of ISR. (c) 2006 Wiley Periodicals, Inc.
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