More Like this

1. Evidence of cryptic methane cycling and non-methanogenic methylamine consumption in the sulfate-reducing zone of sediment in the Santa Barbara Basin, California

   https://doi.org/10.5194/bg-20-4377-2023  

   Krause, Sebastian J.; Liu, Jiarui; Yousavich, David J.; Robinson, DeMarcus; Hoyt, David W.; Qin, Qianhui; Wenzhöfer, Frank; Janssen, Felix; Valentine, David L.; Treude, Tina (January 2023, Biogeosciences)

   Abstract. The recently discovered cryptic methane cycle in the sulfate-reducing zone of marine and wetland sediment couples methylotrophic methanogenesis to anaerobic oxidation of methane (AOM). Here we present evidence of cryptic methane cycling activity within the upper regions of the sulfate-reducing zone, along a depth transect within the Santa Barbara Basin, off the coast of California, USA. The top 0–20 cm of sediment from each station was subjected to geochemical analyses and radiotracer incubations using 35S–SO42-, 14C–mono-methylamine, and 14C–CH4 to find evidence of cryptic methane cycling. Methane concentrations were consistently low (3 to 16 µM) across the depth transect, despite AOM rates increasing with decreasing water depth (from max 0.05 nmol cm−3 d−1 at the deepest station to max 1.8 nmol cm−3 d−1 at the shallowest station). Porewater sulfate concentrations remained high (23 to 29 mM), despite the detection of sulfate reduction activity from 35S–SO42- incubations with rates up to 134 nmol cm−3 d−1. Metabolomic analysis showed that substrates for methanogenesis (i.e., acetate, methanol and methylamines) were mostly below the detection limit in the porewater, but some samples from the 1–2 cm depth section showed non-quantifiable evidence of these substrates, indicating their rapid turnover. Estimated methanogenesis from mono-methylamine ranged from 0.2 to 0.5 nmol cm−3 d−1. Discrepancies between the rate constants (k) of methanogenesis (from 14C–mono-methylamine) and AOM (from either 14C–mono-methylamine-derived 14C–CH4 or from directly injected 14C–CH4) suggest the activity of a separate, concurrent metabolic process directly metabolizing mono-methylamine to inorganic carbon. We conclude that the results presented in this work show strong evidence of cryptic methane cycling occurring within the top 20 cm of sediment in the Santa Barbara Basin. The rapid cycling of carbon between methanogenesis and methanotropy likely prevents major build-up of methane in the sulfate-reducing zone. Furthermore, our data suggest that methylamine is utilized by both methanogenic archaea capable of methylotrophic methanogenesis and non-methanogenic microbial groups. We hypothesize that sulfate reduction is responsible for the additional methylamine turnover, but further investigation is needed to elucidate this metabolic activity. 

   more » « less
2. Nitrogen Redox Controls on Greenhouse Gas Production in Yedoma Taliks

   https://doi.org/10.1111/gcb.70356  

   Bergman, Oded; Walter_Anthony, Katey; Eliani‐Russak, E; Sivan, Orit (July 2025, Global Change Biology)

   ABSTRACT Large carbon and nitrogen pools are disproportionately concentrated in the icy, Pleistocene‐aged silt deposits of Arctic Yedoma permafrost. Upon thaw, these undergo microbial mineralization, releasing greenhouse gases (GHGs) including carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). Here, we present combined geochemical data with microbial function and community dynamics from deep (7‐m) talik soil boreholes in water‐unsaturated yedoma upland in interior Alaska. Our results reveal significant in situ seasonal shifts in microbial function, community composition, and diversity throughout the talik. Methanogenesis persisted in the deep talik year‐round. Winter methanotrophy was negligible within and above the methanogenic zone, leading to elevated CH₄production and emission to the atmosphere. This is likely due to reduced microbial methanotrophic activity associated with lower temperatures and nitrogen availability. During summer, strong aerobic methanotrophy near the soil surface reduced CH₄emissions. Nitrate/nitrite‐mediated anaerobic oxidation of methane (AOM) by both archaea (ANME‐2d clade) and bacteria (NC10 phylum) occurred at and above the anoxic methanogenic zone, further offsetting CH₄production. In contrast to CH4 production potentials, which were higher in surface soils in winter compared to summer, we observed higher N₂O production potentials in summer compared to winter. Nitrous oxide concentrations peaked at 10 cm (7.2 μM) and 105 cm (6.7 μM) and were associated with denitrification; nitrogen‐mediated AOM byMethanoperedens(ANME2d). In the summer only and within the top 1 m of soil, high expression of nitrogen‐related genes (narG, norB, amoA, Annamox, and Feammox) indicated active redox dynamics, potentially providing nitrogen species for AOM. The potential N₂O production in summer may imply higher net GHG emissions from yedoma uplands as climate change leads to longer summers and warmer soils in the future. 

   more » « less
3. Spatial evidence of cryptic methane cycling and methylotrophic metabolisms along a land–ocean transect in salt marsh sediment

   https://doi.org/10.1016/j.gca.2025.07.019  

   Krause, Sebastian JE; Wipfler, Rebecca; Liu, Jiarui; Yousavich, David J; Robinson, DeMarcus; Hoyt, David W; Orphan, Victoria J; Treude, Tina (September 2025, Geochimica et Cosmochimica Acta)

   Methylotrophic methanogenesis in the sulfate-rich zone of coastal and marine sediments couples with anaerobic oxidation of methane (AOM), forming the cryptic methane cycle. This study provides evidence of cryptic methane cycling in the sulfate-rich zone across a land–ocean transect of four stations–two brackish, one marine, and one hypersaline–within the Carpinteria Salt Marsh Reserve (CSMR), southern California, USA. Samples from the top 20 cm of sediment from the transect were analyzed through geochemical and molecular (16S rRNA) techniques, in-vitro methanogenesis incubations, and radiotracer incubations utilizing 35S-SO4, 14C-mono-methylamine, and 14C-CH4. Sediment methane concentrations were consistently low (3 to 28 µM) at all stations, except for the marine station, where methane increased with depth reaching 665 µM. Methanogenesis from mono-methylamine was detected throughout the sediment at all stations with estimated CH4 production rates in the sub-nanomolar to nanomolar range per cm3 sediment and day. 16S rRNA analysis identified methanogenic archaea (Methanosarcinaceae, Methanomassiliicoccales, and Methanonatronarchaeacea) capable of producing methane from methylamines in sediment where methylotrophic methanogenesis was found to be active. Metabolomic analysis of porewater showed mono-methylamine was mostly undetectable (<3 µM) or present in trace amounts (<10 µM) suggesting rapid metabolic turnover. In-vitro methanogenesis incubations of natural sediment showed no linear methane buildup, suggesting a process limiting methane emissions. AOM activity, measured with 14C-CH4, overlapped with methanogenesis from mono-methylamine activity at all stations, with rates ranging from 0.03 to 19.4 nmol cm− 3 d− 1. Geochemical porewater analysis showed the CSMR sediments are rich in sulfate and iron. Porewater sulfate concentrations (9–91 mM) were non-limiting across the transect, supporting sulfate reduction activity (1.5–2,506 nmol cm− 3 d− 1). Porewater sulfide and iron (II) profiles indicated that the sediment transitioned from a predominantly iron-reducing environment at the two brackish stations to a predominantly sulfate-reducing environment at the marine and hypersaline stations, which coincided with the presence of phyla (Desulfobacterota) involved in these processes. AOM activity overlapped with sulfate reduction and porewater iron (II) concentrations suggesting that AOM is likely coupled to sulfate and possibly iron reduction at all stations. However, 16S rRNA analysis identified anaerobic methanotrophs (ANME-2) only at the marine and hypersaline stations while putative methanogens were found in sediment across all stations. In one sediment horizon at the marine station, methanogen families (Methanosarcinaceae, Methanosaetaceae, Methanomassiliicoccales, and Methanoregulaceae) and ANME 2a,2b, and 2c groups were found together. Collectively, our data suggest that at the brackish stations methanogens alone may be involved in cryptic methane cycling, while at the marine and hypersaline stations both groups may be involved in the process. Differences in rate constants from incubations with 14C-labeled methane and mono-methylamine suggest a non-methanogenic process oxidizing mono-methylamine to inorganic carbon, likely mediated by sulfate-reducing bacteria. Understanding the potential competition of sulfate reducers with methanogens for mono-methylamine needs further investigation as it might be another important process responsible for low methane emissions in salt marshes. 

   more » « less
4. Physicochemical perturbation increases nitrous oxide production from denitrification in soils and sediments

   https://doi.org/10.5194/bg-21-4837-2024  

   Weston, Nathaniel B; Troy, Cynthia; Kearns, Patrick J; Bowen, Jennifer L; Porubsky, William; Hyacinthe, Christelle; Meile, Christof; Van_Cappellen, Philippe; Joye, Samantha B (January 2024, Biogeosciences)

   Abstract. Atmospheric concentrations of nitrous oxide (N2O), a potent greenhouse gas that is also responsible for significant stratospheric ozone depletion, have increased in response to the intensified use of agricultural fertilizers and other human activities that have accelerated nitrogen cycling processes. Microbial denitrification in soils and sediments is a major source of N2O, produced as an intermediate during the reduction of oxidized forms of nitrogen to dinitrogen gas (N2). Substrate availability (nitrate and organic matter) and environmental factors such as oxygen levels, temperature, moisture, and pH influence rates of denitrification and N2O production. Here we describe the role of physicochemical perturbation (defined here as a change from the ambient environmental conditions) in influencing rates of denitrification and N2O production. Changes in salinity, temperature, moisture, pH, and zinc in agricultural soils induced a short-term perturbation response characterized by lower rates of total denitrification and higher rates of net N2O production. The ratio of N2O to total denitrification (N2O : DNF) increased strongly with physicochemical perturbation. A salinity press experiment on tidal freshwater marsh soils revealed that increased N2O production was likely driven by transcriptional inhibition of the nitrous oxide reductase (nos) gene and that the microbial community adapted to altered salinity over a relatively short time frame (within 1 month). Perturbation appeared to confer resilience to subsequent disturbance, and denitrifiers from an environment without salinity fluctuations (tidal freshwater estuarine sediments) demonstrated a stronger N2O perturbation response than denitrifiers from environments with more variable salinity (oligohaline and mesohaline estuarine sediments), suggesting that the denitrifying community from physicochemically stable environments may have a stronger perturbation response. These findings provide a framework for improving our understanding of the dynamic nature of N2O production in soils and sediments, in which changes in physical and/or chemical conditions initiate a short-term perturbation response that promotes N2O production that moderates over time and with subsequent physicochemical perturbation. 

   more » « less
5. Goose Feces Effects on Subarctic Soil Nitrogen Availability and Greenhouse Gas Fluxes

   https://doi.org/10.1007/s10021-022-00752-x  

   Beard, Karen H.; Kelsey, Katharine C.; Choi, Ryan T.; Welker, Jeffrey M.; Leffler, A. Joshua (March 2022, Ecosystems)

   Vertebrate herbivore excrement is thought to influence nutrient cycling, plant nutrition, and growth; however, its importance is rarely isolated from other aspects of herbivory, such as trampling and leaf removal, leaving questions about the extent to which herbivore effects are due to feces. We hypothesized that as a source of additional nutrients, feces would directly increase soil N concentrations and N2O emission, alleviate plant, and microbial nutrient limitations, resulting in increased plant growth and foliar quality, and increase CH4 emissions. We tested these hypotheses using a field experiment in coastal western Alaska,USA, where we manipulated goose feces such that naturally grazed areas received three treatments:feces removal, ambient amounts of feces, or double ambient amounts of feces. Doubling feces marginally increased NH4 +-N in soil water, whereas both doubled feces and feces removal significantly increased NO3--N; N2O flux was also higher in removal plots. Feces removal marginally reduced root biomass and significantly reduced productivity (that is, GPP) in the second year, measured as greater CO2 emissions. Doubling feces marginally increased foliar chemical quality by increasing %N and decreasing C:N. Treatments did not influence CH4 flux. In short, feces removal created sites poorer in nutrients, with reduced root growth, graminoid nutrient uptake, and productivity. While goose feces alone did not create dramatic changes in nutrient cycling in western Alaska, they do appear to be an important source of nutrients for grazed areas and to contribute to greenhouse gas exchange as their removal increased emissions of CO2 and N2O to the atmosphere. 

   more » « less