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1. The Effects of Temperature, Flooding, and Goose Feces Addition on Greenhouse Gas Emissions and Ammonification in Four High Latitude Soils. Yukon Delta National Wildlife Refuge, Alaska, 2022.

   https://doi.org/10.18739/A2DR2PB1G  

   Ross, Jenna; Leffler, A Joshua (January 2024, NSF Arctic Data Center)

   The large carbon (C) stock of wetlands is vulnerable to climate change, especially in high latitudes that are warming at a disproportional rate. Likewise, low-lying Arctic areas will experience increased coastal flooding under climate change and sea-level rise, which may alter goose herbivory and fecal deposition patterns if geese are pushed inland. While temperature, flooding, and feces impact soil C emissions, their interactive effects have been rarely studied. Here, we explore the impact of these interactions on carbon dioxide (CO2) and methane (CH4) emissions and nitrogen (N) mineralization (ammonification) in soils collected from four plant communities in the Yukon-Kuskokwim (Y-K) Delta, a high latitude coastal wetland in western Alaska. Communities included a Grazing Lawn, which is intensely grazed and susceptible to flooding, a Lowland Wetland and an Upland Wetland that experience moderate grazing and frequent (Lowland) and less frequent (Upland) flooding, and a rarely grazed and flooded Tundra community, located at the highest elevation. Soils were incubated for 16 weeks at 8 degrees Celsius (°C) or 18°C in microcosms and subjected to flooding and feces addition treatments with no-flood and no-feces controls. We quantified C emissions weekly and ammonification over the course of the experiment. While warming increased ammonification and C demand in the Lowland Wetland and always increased CO2 and CH4 emissions, interactions with flooding complicated warming impacts on C emissions in the Grazing Lawn and Tundra. In the Grazing Lawn, flooding increased CH4 emissions at 8°C and 18 °C, but in the Tundra, flooding suppressed CH4 emissions at 18°C. Flooding alone reduced CO2 emissions in the Upland Wetland. Feces addition increased CO2 emissions in all communities, but feces impacts on CH4 emissions and ammonification were minimal. When feces and flooding occurred together in the Lowland Wetland, CH4 emissions decreased compared to when feces was added without concomitant flood. Feces decreased the immobilization of ammonium and N demand in the Tundra only. Our results suggest that flooding could partially offset C loss from warming in less frequently flooded, higher elevation communities, but this offset could be negligible if flooding and warming drastically increase C loss in more flooded lowland areas. 

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2. Herbivory changes soil microbial communities and greenhouse gas fluxes in a high-latitude wetland

   https://doi.org/10.1007/s00248-021-01733-8  

   Foley, Karen M.; Beard, Karen H.; Atwood, Trisha B.; Waring, Bonnie G. (March 2021, Microbial Ecology)

   null (Ed.)

   Herbivory can have strong impacts on greenhouse gas fluxes in high-latitude ecosystems. For example, in the Yukon-Kuskokwim (Y-K) Delta in western Alaska, migratory goose grazing affects the magnitude of soil carbon dioxide (CO2) and methane (CH4) fluxes. However, the underlying drivers of this relationship are unclear, as few studies systematically tease apart the processes by which herbivores influences soil biogeochemistry. To examine these mechanisms in detail, we conducted a laboratory incubation experiment to quantify changes in greenhouse gas fluxes in response to three parameters altered by herbivores in situ: temperature, soil moisture content, and nutrient inputs. These treatments were applied to soils collected in grazing lawns and nearby ungrazed habitat, allowing us to assess how variation in microbial community structure influenced observed responses. We found pronounced differences in both fungal and prokaryotic community composition between grazed and ungrazed areas. In the laboratory incubation experiment, CO2 and CH4 fluxes increased with temperature, soil moisture, and goose fecal addition, suggesting that grazing-related changes in the soil abiotic environment may enhance soil C losses. Yet, these abiotic drivers were insufficient to explain variation in fluxes between soils with and without prior grazing. Differences in trace gas fluxes between grazed and ungrazed areas may result both from herbivore-induced shifts in abiotic parameters and grazing-related alterations in microbial community structure. Our findings suggest that relationships among herbivores and soil microbial communities could mediate carbon-climate feedbacks in rapidly changing high-latitude ecosystems. 

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3. Herbivory in a low Arctic wetland alters intraspecific plant root traits with consequences for carbon and nitrogen cycling

   https://doi.org/10.1111/1365-2745.70028  

   Chavez, Emily_A; Adkins, Jaron; Waring, Bonnie_G; Beard, Karen_H; Choi, Ryan_T; Miller, Lindsay; Saunders, Taylor; Atwood, Trisha_B (March 2025, Journal of Ecology)

   Abstract High latitude wetlands are ecologically important ecosystems due to their large carbon (C) storage capacity and because they serve as breeding and nesting habitat for large populations of migratory birds. Goose herbivory in wetland meadows affects leaf chemical and morphological traits and also influences soil properties by increasing soil temperature and depositing faeces. Grazing‐induced changes to above‐ground traits and soil properties impact C cycling, but the influence of grazing on root‐mediated C and nitrogen (N) cycling has not been explored.We investigated how goose herbivory in a low‐Arctic coastal wetland in western Alaska affected root morphological, physiological and chemical traits of a dominant graminoid by assessing plant traits in ungrazed versus heavily grazed sedge meadows. We also performed a 11‐week lab‐based root incubation experiment to determine how grazing affects CO₂‐C efflux, the size and decay rate of the fast‐cycling C pool (i.e. C with a mean residence time of days to weeks, determined via CO₂‐C efflux), and patterns of N mineralization during root decomposition.Goose grazing altered root chemical traits by increasing root N by 7%, cellulose by 12%, and ash content by 17%, indicating that grazing shifted root chemical traits towards a resource‐acquisition strategy. Grazing did not alter root biomass, morphology or bulk C exudation. In our root incubation, soils that included the roots of grazed plants tended to exhibit greater CO₂‐C efflux than those containing ungrazed plant roots due to a larger fast‐cycling C pool. Additionally, grazing‐induced increases in soil temperature led to greater CO₂‐C efflux due to a faster decay rate of the fast‐cycling C pool. Finally, compared with ungrazed roots, we found that the decomposition of grazed roots resulted in more N being transferred to root necromass from the surrounding soil, suggesting that microbial communities decomposing grazed roots immobilized N.Synthesis. Overall, our results indicate that goose grazing increased C‐cycling rates by influencing soil environmental conditions and by altering the ecological strategy of grazed plants. In contrast, grazing decreased net N mineralization by promoting N immobilization. These results suggest that changing patterns and abundances of herbivores can have substantial effects on elemental cycles. 

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4. Soil nutrients cause threefold increase in pathogen and herbivore impacts on grassland plant biomass

   https://doi.org/10.1111/1365-2745.14111  

   Zaret, Max; Kinkel, Linda; Borer, Elizabeth T.; Seabloom, Eric W. (August 2023, Journal of Ecology)

   Abstract A combination of theory and experiments predicts that increasing soil nutrients will modify herbivore and microbial impacts on ecosystem carbon cycling.However, few studies of herbivores and soil nutrients have measured both ecosystem carbon fluxes and carbon pools. Even more rare are studies manipulating microbes and nutrients that look at ecosystem carbon cycling responses.We added nutrients to a long‐term, experiment manipulating foliar fungi, soil fungi, mammalian herbivores and arthropods in a low fertility grassland. We measured gross primary production (GPP), ecosystem respiration (ER), net ecosystem exchange (NEE) and plant biomass throughout the growing season to determine how nutrients modify consumer impacts on ecosystem carbon cycling.Nutrient addition increased above‐ground biomass and GPP, but not ER, resulting in an increase in ecosystem carbon uptake rate. Reducing foliar fungi and arthropods increased plant biomass. Nutrients amplified consumer effects on plant biomass, such that arthropods and foliar fungi had a threefold larger impact on above‐ground biomass in fertilized plots.Synthesis. Our work demonstrates that throughout the growing season soil resources modify carbon uptake rates as well as animal and fungal impacts on plant biomass production. Taken together, ongoing nutrient pollution may increase ecosystem carbon uptake and drive fungi and herbivores to have larger impacts on plant biomass production. 

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5. Nutrient availability controls the impact of mammalian herbivores on soil carbon and nitrogen pools in grasslands

   https://doi.org/10.1111/gcb.15023  

   Sitters, Judith; Wubs, E. R. Jasper; Bakker, Elisabeth S.; Crowther, Thomas W.; Adler, Peter B.; Bagchi, Sumanta; Bakker, Jonathan D.; Biederman, Lori; Borer, Elizabeth T.; Cleland, Elsa E.; et al (February 2020, Global Change Biology)

   Abstract Grasslands are subject to considerable alteration due to human activities globally, including widespread changes in populations and composition of large mammalian herbivores and elevated supply of nutrients. Grassland soils remain important reservoirs of carbon (C) and nitrogen (N). Herbivores may affect both C and N pools and these changes likely interact with increases in soil nutrient availability. Given the scale of grassland soil fluxes, such changes can have striking consequences for atmospheric C concentrations and the climate. Here, we use the Nutrient Network experiment to examine the responses of soil C and N pools to mammalian herbivore exclusion across 22 grasslands, under ambient and elevated nutrient availabilities (fertilized with NPK + micronutrients). We show that the impact of herbivore exclusion on soil C and N pools depends on fertilization. Under ambient nutrient conditions, we observed no effect of herbivore exclusion, but under elevated nutrient supply, pools are smaller upon herbivore exclusion. The highest mean soil C and N pools were found in grazed and fertilized plots. The decrease in soil C and N upon herbivore exclusion in combination with fertilization correlated with a decrease in aboveground plant biomass and microbial activity, indicating a reduced storage of organic matter and microbial residues as soil C and N. The response of soil C and N pools to herbivore exclusion was contingent on temperature – herbivores likely cause losses of C and N in colder sites and increases in warmer sites. Additionally, grasslands that contain mammalian herbivores have the potential to sequester more N under increased temperature variability and nutrient enrichment than ungrazed grasslands. Our study highlights the importance of conserving mammalian herbivore populations in grasslands worldwide. We need to incorporate local‐scale herbivory, and its interaction with nutrient enrichment and climate, within global‐scale models to better predict land–atmosphere interactions under future climate change. 

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