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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. Bison grazing increases grass foliar nutrients and drought tolerance at fine spatial scales

   https://doi.org/10.1007/s11104-026-08422-w  

   Wedel, Emily R; Rodriguez-Blash, Taylor; Nippert, Jesse B (April 2026, Plant and Soil)

   Abstract AimsThe American bison is often recognized as an ecological engineer because their grazing and wallowing behavior increases plant diversity and productivity. These disturbances increase spatial heterogeneity and can alter plant nutrient and water dynamics. We assessed how bison grazing and wallowing affect grass chemistry and physiology, and whether grass evolutionary legacies mediate species-specific responses. MethodsWe measured grass drought tolerance, photosynthetic activity, and foliar and soil chemistry in four grass species at Konza Prairie Biological Station (Kansas, USA). Species included two dominant C₄panicoids, one C₃panicoid, and one C₄chloridoid species that becomes dominant in grazed areas. We sampled grasses in grazed areas near and away from bison wallows and adjacent fenced areas that have excluded bison for over 30 years. We assessed intra-annual changes in turgor loss point, maximum leaf electron transport rate, foliar δ¹³C, and C, N, P, and K content. ResultsSoil nutrient concentrations did not vary across locations, but foliar P, K, and N content was highest near bison wallows. Higher foliar N in bison grazed areas was correlated with higher electron transport rate. The chloridoid species showed the greatest response to bison wallows, with lower turgor loss point and higher foliar nutrients near wallows than in adjacent grazed prairie. ConclusionOur results demonstrate that bison grazing creates fine-scale heterogeneity that alters plant nutrient dynamics, photosynthetic capacity, and drought tolerance. These findings suggest that bison engineer ecosystems not only through changes in plant communities but also through the physiological responses of dominant grass species. 

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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. Soil nutrient amendment increases the potential for inter-kingdom resource competition among foliar endophytes

   https://doi.org/10.1093/ismeco/ycae130  

   Hansen, Zoe A; Fulcher, Michael R; Wornson, Nicholas; Spawn-Lee, Seth A; Johnson, Mitch; Song, Zewei; Michalska-Smith, Matthew; May, Georgiana; Seabloom, Eric W; Borer, Elizabeth T; et al (January 2024, ISME Communications)

   Abstract Foliar endophytes play crucial roles in large-scale ecosystem functions such as plant productivity, decomposition, and nutrient cycling. While the possible effects of environmental nutrient supply on the growth and carbon use of endophytic microbes have critical implications for these processes, these impacts are not fully understood. Here, we examined the effects of long-term elevated nitrogen, phosphorus, potassium, and micronutrient (NPKμ) supply on culturable bacterial and fungal foliar endophytes inhabiting the prairie grass Andropogon gerardii. We hypothesized that elevated soil nutrients alter the taxonomic composition and carbon use phenotypes of foliar endophytes and significantly shift the potential for resource competition among microbes within leaves. We observed changes in taxonomic composition and carbon use patterns of fungal, but not bacterial, endophytes of A. gerardii growing in NPKμ-amended versus ambient conditions. Fungal endophytes from NPKμ-amended plants had distinct carbon use profiles and demonstrated greater specialization across carbon sources compared to control plots. Resource niche overlap between bacterial and fungal endophytes also increased with plot nutrient supply, suggesting enhanced potential for inter-kingdom competition. Collectively, this work suggests that soil nutrient enrichment alters how fungal endophyte communities exist in the foliar environment, with potentially significant implications for broad-scale ecosystem function. 

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