TY  - JOUR
AB  - Dissolved organic carbon (DOC) plays critical roles in marine carbon cycling, but its sources and sinks remain uncertain. In this study, we monitored DOC exudation rates of Sargassum natans under visible light (lambda > 390 nm) and solar radiation. DOC release rates ranged from 7 to 10 mu g C g(biomass)(-1) hr(-1) (wet weight) under visible light, but increased to 23 to 41 mu g C g(biomass)(-1) hr(-1) when exposed to natural sunlight. Results indicate that DOC released by Sargassum could amount to 0.3 to 1.2 Tg C/year, potentially contributing significantly to the marine DOC pool in the Gulf of Mexico and Western North Atlantic. We employed the Folin-Ciocalteu phenolic content method, nuclear magnetic resonance (NMR) spectroscopy, and ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to characterize the diverse pool of organic compounds exuded from Sargassum. Results from these complementary methods showed that Sargassum release large quantities of phlorotannins, a class of polyphenols that have very similar properties to terrestrial DOC. These phlorotannins and their oxygenated phenolic derivatives exhibit a high hydrogen deficiency and functionalization (i.e., 4 to 6 oxygen atoms per aromatic ring), representing 5 to 18% of the released DOC isolated by solid phase extraction. Thus, Sargassum is the largest biological source of open ocean polyphenols recorded to date. The amount of polyphenolic DOC released by Sargassum challenges previous beliefs that all polyphenols found within the oceans are remnants of terrestrial organic matter, although the stability of phlorotannins and their derivatives needs to be further evaluated.
AU  - Powers, L.C.*
AU  - Hertkorn, N.
AU  - McDonald, N.*
AU  - Schmitt-Kopplin, P.
AU  - Del Vecchio, R.*
AU  - Blough, N.V.*
AU  - Gonsior, M.*
C1  - 57472
C2  - 47807
CY  - 2000 Florida Ave Nw, Washington, Dc 20009 Usa
SP  - 1423-1439
TI  - Sargassum sp. act as a large regional source of marine dissolved organic carbon and polyphenols.
JO  - Global Biogeochem. Cycles
VL  - 33
IS  - 1
PB  - Amer Geophysical Union
PY  - 2019
SN  - 0886-6236
ER  - 

TY  - JOUR
AB  - The global ocean contains a massive reservoir of dissolved organic carbon (DOC), rivaling the atmosphere's pool of CO2. The most recalcitrant fractions have mean radiocarbon ages of similar to 4,000years in the Atlantic to similar to 6,000years in the Pacific. Knowing the radiocarbon signatures of DOC and the molecular composition of dissolved organic matter (DOM) is crucial to develop understanding of the persistence and lifetime of the DOC pool. In this research, we collected samples from the deep North Pacific in August 2013 (aboard the RV Melville) to couple the Delta C-14 content of solid-phase-extracted DOM (Delta C-14-SPE-DOM) with its molecular composition in the ocean's oldest deep waters. We find that deep waters in this region held a mean Delta C-14-SPE-DOM value of -554 +/- 9 (similar to 6,400(14)Cyears), substantially more depleted than that in the deep Atlantic, which held a mean Delta C-14-SPE-DOM value of -445 +/- 5. While we find a more degraded molecular composition of DOM in the deep Pacific than the deep Atlantic, the molecular formulae within the Island of Stability (Lechtenfeld et al., 2014, ), are largely retained. These results imply that a fraction of deep DOM is resistant to removal and present in both the deep Atlantic and Pacific Oceans.
AU  - Bercovici, S.K.*
AU  - Koch, B.P.*
AU  - Lechtenfeld, O.J.*
AU  - McCallister, S.L.*
AU  - Schmitt-Kopplin, P.
AU  - Hansell, D.A.*
C1  - 54510
C2  - 45645
CY  - 2000 Florida Ave Nw, Washington, Dc 20009 Usa
SP  - 1449-1456
TI  - Ageing and molecular changes of dissolved organic matter between two deep oceanic end members.
JO  - Global Biogeochem. Cycles
VL  - 32
IS  - 10
PB  - Amer Geophysical Union
PY  - 2018
SN  - 0886-6236
ER  - 

TY  - JOUR
AB  - In order to investigate the link between the methane dynamics in permafrost deposits and climate changes in the past, we studied the abundance, composition, and methane production of methanogenic communities in Late Pleistocene and Holocene sediments of the Siberian Arctic. We detected intervals of increased methane concentrations in Late Pleistocene and Holocene deposits along a 42 ka old permafrost sequence from Kurungnakh Island in the Lena Delta (northeast Siberia). Increased amounts of archaeal life markers (intact phospholipid ethers) and a high variety in genetic fingerprints detected by 16S ribosomal ribonucleic acid gene analyses of methanogenic archaea suggest presently living and presumably active methanogenic archaea in distinct layers predominantly in Holocene deposits, but also in deep frozen ground at 17 m depth. Potential methanogenic activity was confirmed by incubation experiments. By comparing methane concentrations, microbial incubation experiments, gene analysis of methanogens, and microbial life markers (intact phospholipid esters and ethers) to already partly degraded membrane lipids, such as archaeol and isoprenoid glycerol dialkyl glycerol tetraethers, we demonstrated that archaeol likely represents a signal of past methanogenic archaea. The archaeol signal was used to reconstruct the response of methanogenic communities to past temperature changes in the Siberian Arctic, and the data suggest higher methane emissions occurred during warm periods, particularly during an interval in the Late Pleistocene and during the Holocene. This new data on present and past methanogenic communities in the Siberian terrestrial permafrost imply that these microorganisms will respond to the predicted future temperature rise in the Arctic with increasing methane production, as demonstrated in previous warmer periods.
AU  - Bischoff, J.*
AU  - Mangelsdorf, K.*
AU  - Gattinger, A.*
AU  - Schloter, M.
AU  - Kurchatova, A.N.*
AU  - Herzschuh, U.*
AU  - Wagner, D.E.*
C1  - 23769
C2  - 31279
SP  - 305-317
TI  - Response of methanogenic archaea to Late Pleistocene and Holocene climate changes in the Siberian Arctic.
JO  - Global Biogeochem. Cycles
VL  - 27
IS  - 2
PB  - Amer. Geophysical Union
PY  - 2013
SN  - 0886-6236
ER  - 

TY  - JOUR
AB  - Biodiversity is expected to improve ecosystem services, e. g., productivity or seepage water quality. The current view of plant diversity effects on element cycling is based on short-term grassland studies that discount possibly slow belowground feedbacks to aboveground diversity. Furthermore, these grasslands were established on formerly arable land associated with changes in soil properties, e. g., accumulation of organic matter. We hypothesize that the plant diversity-N cycle relationship changes with time since establishment. We assessed the relationship between plant diversity and (1) aboveground and soil N storage and (2) NO(3)-N and NH(4)-N availability in soil between 2003 and 2007 in the Jena Experiment, a grassland experiment established in 2002 in which the number of plant species varied from 1 to 60. The positive effect of plant diversity on aboveground N storage (mainly driven by biomass production) tended to increase through time. The initially negative correlation between plant diversity and soil NO(3)-N availability disappeared after 2003. In 2006 and 2007, a positive correlation between plant diversity and soil NH(4)-N availability appeared which coincided with a positive correlation between plant diversity and N mineralized from total N accumulated in soil. We conclude that the plant diversity-N cycle relationship in newly established grasslands changes with time because of accumulation of organic matter in soil associated with the establishment. While a positive relationship between plant diversity and soil N storage improves soil fertility and reduces fertilizing needs, increasingly closed N cycling with increasing plant diversity as illustrated by decreased NO(3)-N concentrations in diverse mixtures reduces the negative impact of agricultural N leaching on groundwater resources.
AU  - Oelmann, Y.*
AU  - Buchmann, N.*
AU  - Gleixner, G.*
AU  - Habekost, M.*
AU  - Roscher, C.*
AU  - Rosenkranz, S.*
AU  - Schulze, E.D.*
AU  - Steinbeiss, S.
AU  - Temperton, V.M.*
AU  - Weigelt, A.*
AU  - Weisser, W.W.*
AU  - Wilcke, W.*
C1  - 6475
C2  - 28751
CY  - Washington, USA
TI  - Plant diversity effects on aboveground and belowground N pools in temperate grassland ecosystems: Development in the first 5 years after establishment.
JO  - Global Biogeochem. Cycles
VL  - 25
IS  - 2
PB  - Amer. Geophysical Union
PY  - 2011
SN  - 0886-6236
ER  - 

TY  - JOUR
AU  - Dittmar, T.*
AU  - Hertkorn, N.
AU  - Kattner, G.*
AU  - Lara, R.J.*
C1  - 5807
C2  - 24292
SP  - GB1012 (1-7)
TI  - Mangroves, a major source of dissolved organic carbon of the oceans.
JO  - Global Biogeochem. Cycles
VL  - 20
PY  - 2006
SN  - 0886-6236
ER  -