Evaluation of Organic Geochemical Proxies in Sediments as Recorders of the History of Biogeochemical Dynamics in Lake Erie over the Last Century.

Against a background of a well documented and reconstructed paleoenvironmental history of Lake Erie over the last century, the reliability and accuracy of commonly used organic geochemical proxies from sediments in paleoenvironment reconstructions were evaluated. Carbon cycling in Lake Erie is reflected by stable carbon isotopes of total organic carbon and calcium carbonate (δ13Corg and δ13Ccaco3), total organic carbon concentrations (TOC) and calcium carbonate concentrations (CaCO3). δ13Corg and TOC both record changes in lacustrine productivity and nutrient loadings reliably and directly. CaCO3 contents are primarily controlled by decomposition of TOC in the hypolimnion and sediments, reflecting the carbon cycling between the epilimnion and hypoliminion/sediment. The carbon cycling process indicated by δ13Ccaco3 variations is complicated and appears to relate to primary productivity, temperature variations, phosphorus distributions and/or the recycling of 12C in the epilimnion. Although stable nitrogen isotopes (δ15N) reflect nitrogen cycling, they also record multiple biogeochemical processes, including anthropogenic inputs, denitrification, primary productivity and establishment of invasive species at different stages of lacustrine history, rendering the interpretations of δ15N as paleoenvironmental proxies difficult. The concentrations of biomarker molecules, including hydrocarbons (HCs), fatty acids (FAs) and fatty alcohols (OLs), reliably record changes of lacustrine productivity while their molecular distributions reflect various aspects of paleoenvironmental conditions. The degree of post-burial diagenesis is closed linked with the abundance of branched and unsaturated FAs. When used together, carbon-chain lengths of FAs and OLs may reliably reflect the relative importance between terrigenous and aquatic sources for organic matter. Speculatively, uncommon HC distributions originate from microorganisms inhibiting an oil-contaminated environment. The effects of spatial and temporal variability of sediment cores on paleoenvironmental reconstructions are investigated by comparing four cores sampled at a common location but in different years, i.e., 1982, 1988, 1991 and 2003. The approximately consistent temporal trends of organic geochemical proxies in these four cores suggest both spatial and temporal variability are not significant enough in biasing long-term paleoenvironmental interpretations. Nevertheless, the differences among the cores in year-to-year proxy variations and proxy values, which are mainly accounted by spatial variability of sediment cores, indicate that high-resolution (i.e. annual) paleoenvironmental interpretations may not be reliable.Ph.D.Oceanography: Marine Geology and GeochemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/61679/1/luyuehan_1.pd

Photochemical and microbial alteration of dissolved organic matter in temperate headwater streams associated with different land use

Photochemical and microbial transformations of DOM were evaluated in headwater streams draining forested and human-modified lands (pasture, cropland, and urban development) by laboratory incubations. Changes in DOC concentrations, DOC isotopic signatures, and DOM fluorescence properties were measured to assess the amounts, sources, ages, and properties of reactive and refractory DOM under the influence of photochemistry and/or bacteria. DOC in streams draining forest-dominated watersheds was more photoreactive than in streams draining mostly human-modified watersheds, possibly due to greater contributions of terrestrial plant-derived DOC and lower amounts of prior light exposure in forested streams. Overall, the percentage of photoreactive DOC in stream waters was best predicted by the relative content of terrestrial fluorophores. The bioreactivity of DOC was similar in forested and human-modified streams, but variations were correlated with temperature and may be further controlled by the diagenetic status of organic matter. Alterations to DOC isotopes and DOM fluorescence properties during photochemical and microbial incubations were similar between forested and human-modified streams and included (1) negligible effects of microbial alteration on DOC isotopes and DOM fluorescence properties, (2) selective removal of C-13-depleted and C-14-enriched DOC under the combined influence of photochemical and microbial processes, and (3) photochemical alteration of DOM resulting in a preferential loss of terrestrial humic fluorescence components relative to microbial fluorescence components. This study provides a unique comparison of DOC reactivity in a regional group of streams draining forested and human-modified watersheds and indicates the importance of land use on the photoreactivity of DOC exported from upstream watersheds

Different carboxyl-rich alicyclic molecules proxy compounds select distinct bacterioplankton for oxidation of dissolved organic matter in the mesopelagic Sargasso Sea

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Liu, S., Parsons, R., Opalk, K., Baetge, N., Giovannoni, S., Bolanos, L. M., Kujawinski, E. B., Longnecker, K., Lu, Y., Halewood, E., & Carlson, C. A. Different carboxyl-rich alicyclic molecules proxy compounds select distinct bacterioplankton for oxidation of dissolved organic matter in the mesopelagic Sargasso Sea. Limnology and Oceanography, (2020), doi:10.1002/lno.11405.Marine dissolved organic matter (DOM) varies in its recalcitrance to rapid microbial degradation. DOM of varying recalcitrance can be exported from the ocean surface to depth by subduction or convective mixing and oxidized over months to decades in deeper seawater. Carboxyl‐rich alicyclic molecules (CRAM) are characterized as a major component of recalcitrant DOM throughout the oceanic water column. The oxidation of CRAM‐like compounds may depend on specific bacterioplankton lineages with oxidative enzymes capable of catabolizing complex molecular structures like long‐chain aliphatics, cyclic alkanes, and carboxylic acids. To investigate the interaction between bacteria and CRAM‐like compounds, we conducted microbial remineralization experiments using several compounds rich in carboxyl groups and/or alicyclic rings, including deoxycholate, humic acid, lignin, and benzoic acid, as proxies for CRAM. Mesopelagic seawater (200 m) from the northwest Sargasso Sea was used as media and inoculum and incubated over 28 d. All amendments demonstrated significant DOC removal (2–11 μmol C L−1) compared to controls. Bacterioplankton abundance increased significantly in the deoxycholate and benzoic acid treatments relative to controls, with fast‐growing Spongiibacteracea, Euryarcheaota, and slow‐growing SAR11 enriched in the deoxycholate treatment and fast‐growing Alteromonas, Euryarcheaota, and Thaumarcheaota enriched in the benzoic acid treatment. In contrast, bacterioplankton grew slower in the lignin and humic acid treatments, with oligotrophic SAR202 becoming significantly enriched in the lignin treatment. Our results indicate that the character of the CRAM proxy compounds resulted in distinct bacterioplankton removal rates of DOM and affected specific lineages of bacterioplankton capable of responding.We thank Z. Landry for the inspiring idea of SAR202 catabolism of CRAM. We thank the University of California, Santa Barbara Marine Science Institute Analytical Laboratory for analyzing inorganic nutrient samples. We thank C. Johnson for her help in FISH sample processing and BATS group in supporting our project. We thank N. K. Rubin‐Saika and R. Padula for their help with amino acid sample preparation. We thank Z. Liu, J. Xue, K. Lu, and Y. Shen for their help with amino acid protocol development and validation. We thank B. Stephens for his help on microscopic image analysis. We thank M. Dasenko and the staff of the CGRB at Oregon State University for amplicon library preparation and DNA sequencing. We are grateful for the help provided by the officers and crews of the R/V Atlantic Explorer. Bermuda Institute of Ocean Sciences (BIOS) provides us tremendous support in terms of facilities and lab space. We thank Bermuda government for its allowance of our water sampling and sample export (export permit number SP160904, issued 07 October 2016 under the Fisheries Act, 1972). This project was supported by Simons Foundation International's BIOS‐SCOPE program

Use of ESI-FTICR-MS to Characterize Dissolved Organic Matter in Headwater Streams Draining Forest-Dominated and Pasture-Dominated Watersheds

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) has proven to be a powerful technique revealing complexity and diversity of natural DOM molecules, but its application to DOM analysis in grazing-impacted agricultural systems remains scarce. In the present study, we presented a case study of using ESI-FTICR-MS in analyzing DOM from four headwater streams draining forest-or pasture-dominated watersheds in Virginia, USA. In all samples, most formulas were CHO compounds (71.8-87.9%), with other molecular series (CHOS, CHON, CHONS, and CHOP (N, S)) accounting for only minor fractions. All samples were dominated by molecules falling in the lignin-like region (H/C = 0.7-1.5, O/C = 0.1-0.67), suggesting the predominance of allochthonous, terrestrial plant-derived DOM. Relative to the two pasture streams, DOM formulas in the two forest streams were more similar, based on Jaccard similarity coefficients and nonmetric multidimensional scaling calculated from Bray-Curtis distance. Formulas from the pasture streams were characterized by lower proportions of aromatic formulas and lower unsaturation, suggesting that the allochthonous versus autochthonous contributions of organic matter to streams were modified by pasture land use. The number of condensed aromatic structures (CAS) was higher for the forest streams, which is possibly due to the controlled burning in the forest-dominated watersheds and suggests that black carbon was mobilized from soils to streams. During 15-day biodegradation experiments, DOM from the two pasture streams was altered to a greater extent than DOM from the forest streams, with formulas with H/C and O/C ranges similar to protein (H/C = 1.5-2.2, O/C = 0.3-0.67), lipid (H/C = 1.5-2.0, O/C = 0-0.3), and unsaturated hydrocarbon (H/C = 0.7-1.5, O/C = 0-0.1) being the most bioreactive groups. Aromatic compound formulas including CAS were preferentially removed during combined light+bacterial incubations, supporting the contention that black carbon is labile to light alterations. Collectively, our data demonstrate that head-water DOM composition contains integrative information on watershed sources and processes, and the application of ESI-FTICR-MS technique offers additional insights into compound composition and reactivity unrevealed by fluorescence and stable carbon isotopic measurements

Effects of nitrogen fertilization and bioenergy crop type on topsoil organic carbon and total Nitrogen contents in middle Tennessee USA

Nitrogen (N) fertilization affects bioenergy crop growth and productivity and consequently carbon (C) and N contents in soil, it however remains unclear whether N fertilization and crop type individually or interactively influence soil organic carbon (SOC) and total N (TN). In a three-year long fertilization experiment in switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.) croplands in Middle Tennessee USA, soil samples (0–15cm) were collected in plots with no N input (NN), low N input (LN: 84 kg N ha-1 yr-1 in urea) and high N input (HN: 168 kg N ha-1 yr-1 in urea). Besides SOC and TN, the aboveground plant biomass was also quantified. In addition to a summary of published root morphology data based on a separated mesocosm experiment, the root leachable dissolved organic matter (DOM) of both crops was also measured using archived samples. Results showed no significant interaction of N fertilization and crop type on SOC, TN or plant aboveground biomass (ABG). Relative to NN, HN (not LN) significantly increased SOC and TN in both crops. Though SG showed a 15–68% significantly higher ABG than GG, GG showed a 9.3–12% significantly higher SOC and TN than SG. The positive linear relationships of SOC or TN with ABG were identified for SG. However, GG showed structurally more complex and less readily decomposed root DOM, a larger root volume, total root length and surface area than SG. Collectively, these suggested that intensive N fertilization could increase C and N stocks in bioenergy cropland soils but these effects may be more likely mediated by the aboveground biomass in SG and root chemistry and morphology in GG. Future studies are expected to examine the root characteristics in different bioenergy croplands under the field fertilization experiment

Nitrogen Fertilization Restructured Spatial Patterns of Soil Organic Carbon and Total Nitrogen in Switchgrass and Gamagrass Croplands in Tennessee USA

Nitrogen (N) fertilizers can potentially alter spatial distribution of soil organic carbon (SOC) and total nitrogen (TN) concentrations in croplands such as switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.), but it remains unclear whether these effects are the same between crops and under different rates of fertilization. 13C and 15N are two important proxy measures of soil biogeochemistry, but they were rarely examined as to their spatial distributions in soil. Based on a three-year long fertilization experiment in Middle Tennessee, USA, the top mineral horizon soils (0–15 cm) were collected using a spatially explicit design within two 15-m2 plots under three fertilization treatments in SG and GG croplands. A total of 288 samples were collected based on 12 plots and 24 samples in each plot. The fertilization treatments were no N input (NN), low N input (LN: 84 kg N ha−1 in urea) and high N input (HN: 168 kg N ha−1 in urea). The SOC, TN, SOC/TN (C: N), δ13C and δ15N were quantified and their within-plot variations and spatial distributions were achieved via descriptive and geostatistical methods. Results showed that SG generally displayed 10~120% higher plot-level variations in all variables than GG, and the plot-level variations were 20~77% higher in NN plots than LN and HN plots in SG but they were comparable in unfertilized and fertilized plots in GG. Relative to NN, LN and HN showed more significant surface trends and spatial structures in SOC and TN in both croplands, and the fertilization effect appeared more pronounced in SG. Spatial patterns in C: N, δ13C and δ15N were comparable among different fertilization treatments in both croplands. The descending within-plot variations were also identified among variables (SOC \u3e TN \u3e δ15N \u3e C: N \u3e δ13C). This study demonstrated that N fertilizations generally reduced the plot-level variance and simultaneously re-established spatial structures of SOC and TN in bioenergy croplands, which little varied with fertilization rate but was more responsive in switchgrass cropland

Targeting oncogenic miR-335 inhibits growth and invasion of malignant astrocytoma cells

<p>Abstract</p> <p>Background</p> <p>Astrocytomas are the most common and aggressive brain tumors characterized by their highly invasive growth. Gain of chromosome 7 with a hot spot at 7q32 appears to be the most prominent aberration in astrocytoma. Previously reports have shown that microRNA-335 (miR-335) resided on chromosome 7q32 is deregulated in many cancers; however, the biological function of miR-335 in astrocytoma has yet to be elucidated.</p> <p>Results</p> <p>We report that miR-335 acts as a tumor promoter in conferring tumorigenic features such as growth and invasion on malignant astrocytoma. The miR-335 level is highly elevated in C6 astrocytoma cells and human malignant astrocytomas. Ectopic expression of miR-335 in C6 cells dramatically enhances cell viability, colony-forming ability and invasiveness. Conversely, delivery of antagonist specific for miR-335 (antagomir-335) to C6 cells results in growth arrest, cell apoptosis, invasion repression and marked regression of astrocytoma xenografts. Further investigation reveals that miR-335 targets disheveled-associated activator of morphogenesis 1(Daam1) at posttranscriptional level. Moreover, silencing of endogenous Daam1 (siDaam1) could mimic the oncogenic effects of miR-335 and reverse the growth arrest, proapoptotic and invasion repression effects induced by antagomir-335. Notably, the oncogenic effects of miR-335 and siDAAM1 together with anti-tumor effects of antagomir-335 are also confirmed in human astrocytoma U87-MG cells.</p> <p>Conclusion</p> <p>These findings suggest an oncogenic role of miR-335 and shed new lights on the therapy of malignant astrocytomas by targeting miR-335.</p

Pump it Up workshop report

Workshop held 28-29 September 2017, Cape Cod, MAA two-day workshop was conducted to trade ideas and brainstorm about how to advance our understanding of the ocean’s biological pump. The goal was to identify the most important scientific issues that are unresolved but might be addressed with new and future technological advances