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1. On the formation of complex organic molecules in the interstellar medium: untangling the chemical complexity of carbon monoxide–hydrocarbon containing ice analogues exposed to ionizing radiation via a combined infrared and reflectron time-of-flight analysis

   https://doi.org/10.1039/C9CP01793C  

   Abplanalp, Matthew J. ; Kaiser, Ralf I. ( August 2019 , Physical Chemistry Chemical Physics)

   Recently, over 200 molecules have been detected in the interstellar medium (ISM), with about one third being complex organic molecules (COMs), molecules containing six or more atoms. Over the last few decades, astrophysical laboratory experiments have shown that several COMs are formed via interaction of ionizing radiation within ices deposited on interstellar dust particles at 10 K (H 2 O, CH 3 OH, CO, CO 2 , CH 4 , NH 3 ). However, there is still a lack of understanding of the chemical complexity that is available through individual ice constituents. The present research investigates experimentally the synthesis of carbon, hydrogen, and oxygen bearing COMs from interstellar ice analogues containing carbon monoxide (CO) and methane (CH 4 ), ethane (C 2 H 6 ), ethylene (C 2 H 4 ), or acetylene (C 2 H 2 ) exposed to ionizing radiation. Utilizing online and in situ techniques, such as infrared spectroscopy and tunable photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS), specific isomers produced could be characterized. A total of 12 chemically different groups were detected corresponding to C 2 H n O ( n = 2, 4, 6), C 3 H n O ( n = 2, 4, 6, 8),more »C 4 H n O ( n = 4, 6, 8, 10), C 5 H n O ( n = 4, 6, 8, 10), C 6 H n O ( n = 4, 6, 8, 10, 12, 14), C 2 H n O 2 ( n = 2, 4), C 3 H n O 2 ( n = 4, 6, 8), C 4 H n O 2 ( n = 4, 6, 8, 10), C 5 H n O 2 ( n = 6, 8), C 6 H n O 2 ( n = 8, 10, 12), C 4 H n O 3 ( n = 4, 6, 8), and C 5 H n O 3 ( n = 6, 8). More than half of these isomer specifically identified molecules have been identified in the ISM, and the remaining COMs detected here can be utilized to guide future astronomical observations. Of these isomers, three groups – alcohols, aldehydes, and molecules containing two of these functional groups – displayed varying degrees of unsaturation. Also, the detection of 1-propanol, 2-propanol, 1-butanal, and 2-methyl-propanal has significant implications as the propyl and isopropyl moieties (C 3 H 7 ), which have already been detected in the ISM via propyl cyanide and isopropyl cyanide, could be detected in our laboratory studies. General reaction mechanisms for their formation are also proposed, with distinct follow-up studies being imperative to elucidate the complexity of COMs synthesized in these ices.« less
2. Oxo dicopper anchored on carbon nitride for selective oxidation of methane

   https://doi.org/10.1038/s41467-022-28987-1  

   Xie, Pengfei ; Ding, Jing ; Yao, Zihao ; Pu, Tiancheng ; Zhang, Peng ; Huang, Zhennan ; Wang, Canhui ; Zhang, Junlei ; Zecher-Freeman, Noah ; Zong, Han ; et al ( December 2022 , Nature Communications)

   Abstract Selective conversion of methane (CH 4 ) into value-added chemicals represents a grand challenge for the efficient utilization of rising hydrocarbon sources. We report here dimeric copper centers supported on graphitic carbon nitride (denoted as Cu 2 @C 3 N 4 ) as advanced catalysts for CH 4 partial oxidation. The copper-dimer catalysts demonstrate high selectivity for partial oxidation of methane under both thermo- and photocatalytic reaction conditions, with hydrogen peroxide (H 2 O 2 ) and oxygen (O 2 ) being used as the oxidizer, respectively. In particular, the photocatalytic oxidation of CH 4 with O 2 achieves >10% conversion, and >98% selectivity toward methyl oxygenates and a mass-specific activity of 1399.3 mmol g Cu −1 h −1 . Mechanistic studies reveal that the high reactivity of Cu 2 @C 3 N 4 can be ascribed to symphonic mechanisms among the bridging oxygen, the two copper sites and the semiconducting C 3 N 4 substrate, which do not only facilitate the heterolytic scission of C-H bond, but also promotes H 2 O 2 and O 2 activation in thermo- and photocatalysis, respectively.
3. Large Hydrogen Isotope Fractionation Distinguishes Nitrogenase-Derived Methane from Other Methane Sources

   https://doi.org/10.1128/AEM.00849-20  

   Luxem, Katja E. ; Leavitt, William D. ; Zhang, Xinning ; Atomi, Haruyuki ( September 2020 , Applied and Environmental Microbiology)

   ABSTRACT Biological nitrogen fixation is catalyzed by the enzyme nitrogenase. Two forms of this metalloenzyme, the vanadium (V)- and iron (Fe)-only nitrogenases, were recently found to reduce small amounts of carbon dioxide (CO 2 ) into the potent greenhouse gas methane (CH 4 ). Here, we report carbon ( 13 C/ 12 C) and hydrogen ( 2 H/ 1 H) stable isotopic compositions and fractionations of methane generated by V- and Fe-only nitrogenases in the metabolically versatile nitrogen fixer Rhodopseudomonas palustris . The stable carbon isotope fractionation imparted by both forms of alternative nitrogenase are within the range observed for hydrogenotrophic methanogenesis ( 13 α CO2/CH4 = 1.051 ± 0.002 for V-nitrogenase and 1.055 ± 0.001 for Fe-only nitrogenase; values are means ± standard errors). In contrast, the hydrogen isotope fractionations ( 2 α H2O/CH4 = 2.071 ± 0.014 for V-nitrogenase and 2.078 ± 0.018 for Fe-only nitrogenase) are the largest of any known biogenic or geogenic pathway. The large 2 α H2O/CH4 shows that the reaction pathway nitrogenases use to form methane strongly discriminates against 2 H, and that 2 α H2O/CH4 distinguishes nitrogenase-derived methane from all other known biotic and abiotic sources. These findings on nitrogenase-derived methane will help constrain carbon and nitrogen flows in microbialmore »communities and the role of the alternative nitrogenases in global biogeochemical cycles. IMPORTANCE All forms of life require nitrogen for growth. Many different kinds of microbes living in diverse environments make inert nitrogen gas from the atmosphere bioavailable using a special enzyme, nitrogenase. Nitrogenase has a wide substrate range, and, in addition to producing bioavailable nitrogen, some forms of nitrogenase also produce small amounts of the greenhouse gas methane. This is different from other microbes that produce methane to generate energy. Until now, there was no good way to determine when microbes with nitrogenases are making methane in nature. Here, we present an isotopic fingerprint that allows scientists to distinguish methane from microbes making it for energy versus those making it as a by-product of nitrogen acquisition. With this new fingerprint, it will be possible to improve our understanding of the relationship between methane production and nitrogen acquisition in nature.« less
4. Defining the Sphagnum Core Microbiome across the North American Continent Reveals a Central Role for Diazotrophic Methanotrophs in the Nitrogen and Carbon Cycles of Boreal Peatland Ecosystems

   https://doi.org/10.1128/mbio.03714-21  

   Kolton, Max ; Weston, David J. ; Mayali, Xavier ; Weber, Peter K. ; McFarlane, Karis J. ; Pett-Ridge, Jennifer ; Somoza, Mark M. ; Lietard, Jory ; Glass, Jennifer B. ; Lilleskov, Erik A. ; et al ( February 2022 , mBio)

   Martiny, Jennifer B. (Ed.)

   ABSTRACT Peat mosses of the genus Sphagnum are ecosystem engineers that frequently predominate over photosynthetic production in boreal peatlands. Sphagnum spp. host diverse microbial communities capable of nitrogen fixation (diazotrophy) and methane oxidation (methanotrophy), thereby potentially supporting plant growth under severely nutrient-limited conditions. Moreover, diazotrophic methanotrophs represent a possible “missing link” between the carbon and nitrogen cycles, but the functional contributions of the Sphagnum -associated microbiome remain in question. A combination of metagenomics, metatranscriptomics, and dual-isotope incorporation assays was applied to investigate Sphagnum microbiome community composition across the North American continent and provide empirical evidence for diazotrophic methanotrophy in Sphagnum -dominated ecosystems. Remarkably consistent prokaryotic communities were detected in over 250 Sphagnum SSU rRNA libraries from peatlands across the United States (5 states, 17 bog/fen sites, 18 Sphagnum species), with 12 genera of the core microbiome comprising 60% of the relative microbial abundance. Additionally, nitrogenase ( nifH ) and SSU rRNA gene amplicon analysis revealed that nitrogen-fixing populations made up nearly 15% of the prokaryotic communities, predominated by Nostocales cyanobacteria and Rhizobiales methanotrophs. While cyanobacteria comprised the vast majority (>95%) of diazotrophs detected in amplicon and metagenome analyses, obligate methanotrophs of the genus Methyloferula (order Rhizobiales ) accounted for one-quartermore »of transcribed nifH genes. Furthermore, in dual-isotope tracer experiments, members of the Rhizobiales showed substantial incorporation of 13 CH 4 and 15 N 2 isotopes into their rRNA. Our study characterizes the core Sphagnum microbiome across large spatial scales and indicates that diazotrophic methanotrophs, here defined as obligate methanotrophs of the rare biosphere ( Methyloferula spp. of the Rhizobiales ) that also carry out diazotrophy, play a keystone role in coupling of the carbon and nitrogen cycles in nutrient-poor peatlands. IMPORTANCE Nitrogen availability frequently limits photosynthetic production in Sphagnum moss-dominated high-latitude peatlands, which are crucial carbon-sequestering ecosystems at risk to climate change effects. It has been previously suggested that microbial methane-fueled fixation of atmospheric nitrogen (N 2 ) may occur in these ecosystems, but this process and the organisms involved are largely uncharacterized. A combination of omics (DNA and RNA characterization) and dual-isotope incorporation approaches illuminated the functional diversity of Sphagnum -associated microbiomes and defined 12 bacterial genera in its core microbiome at the continental scale. Moreover, obligate diazotrophic methanotrophs showed high nitrogen fixation gene expression levels and incorporated a substantial amount of atmospheric nitrogen and methane-driven carbon into their biomass. Thus, these results point to a central role for members of the rare biosphere in Sphagnum microbiomes as keystone species that couple nitrogen fixation to methane oxidation in nutrient-poor peatlands.« less
5. Greenhouse gas balance in global pasturelands and rangelands

   https://doi.org/10.1088/1748-9326/abaa79  

   Dangal, Shree R. S. ; Tian, Hanqin ; Pan, Shufen ; Zhang, Lei ; Xu, Rongting ( September 2020 , Environmental Research Letters)

   Grassland ecosystems play an essential role in climate regulation through carbon (C) storage in plant and soil. But, anthropogenic practices such as livestock grazing, grazing related excreta nitrogen (N) deposition, and manure/fertilizer N application have the potential to reduce the effectiveness of grassland C sink through increased nitrous oxide (N₂O) and methane (CH₄) emissions. Although the effect of anthropogenic activities on net greenhouse gas (GHG) fluxes in grassland ecosystems have been investigated at local to regional scales, estimates of net GHG balance at the global scale remains uncertain. With the data-model framework integrating empirical estimates of livestock CH₄emissions with process-based modeling estimates of land CO₂, N₂O and CH₄fluxes, we examined the overall global warming potential (GWP) of grassland ecosystems during 1961–2010. We then quantified the grassland-specific and regional variations to identify hotspots of GHG fluxes. Our results show that, over a 100-year time horizon, grassland ecosystems sequestered a cumulative total of 113.9 Pg CO₂-eq in plant and soil, but then released 91.9 Pg CO₂-eq to the atmosphere, offsetting 81% of the net CO₂sink. We also found large grassland-specific variations in net GHG fluxes, withpasturelandsacting as a small GHG source of 1.52 ± 143 Tg CO₂-eq yr⁻¹(mean ± 1.0 s.d.)more »andrangelandsa strong GHG sink (−442 ± 266 Tg CO₂-eq yr⁻¹) during 1961–2010. Regionally, Europe acted as a GHG source of 23 ± 10 Tg CO₂-eq yr⁻¹, while other regions (i.e. Africa, Southern Asia) were strong GHG sinks during 2001–2010. Our study highlights the importance of considering regional and grassland-specific differences in GHG fluxes for guiding future management and climate mitigation strategies in global grasslands.

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