| Summary: | Nontechnical Release of carbon frozen in permafrost (frozen ground) has been identified as one of the strongest and most likely positive feedbacks between the biosphere and the warming climate. Permafrost nitrogen release has the potential to stabilize the response of the carbon cycle to climate warming because it is a negative, within-system feedback. It could confer resilience to ecosystem-atmosphere interactions in a warming Arctic. The research under this award will advance understanding of the arctic system by incorporating this feedback into a terrestrial biosphere model used extensively by the community for forecasting arctic environmental change and its links to the Earth system. The collaborative nature of the project will build partnerships between ecosystem ecologists and molecular biologists, creating new knowledge about the role of plant-fungal mutualisms in Earth system feedback cycles. The project will support career development of two female arctic scientists at the postdoctoral or new faculty level. It will contribute to the training of two graduate students in biogeosciences, ecology, and molecular biology, and provide an authentic field or laboratory research experience for about twenty undergraduate students. The project will contribute to broadening participation of under-represented groups in ecological and environmental sciences. Technical About 1,700 Pg of organic carbon (C) reside in the permafrost soils and sediments of Arctic and Boreal regions. Because this stock is more than twice the size of the atmospheric C pool, there is considerable interest in understanding how the C balance of permafrost ecosystems will respond to observed and predicted climate warming. As permafrost soils thaw, organic matter that has been cryogenically protected for hundreds to thousands of years is exposed to microbial decomposition and released to the atmosphere as greenhouse gases. One key factor that may strongly influence C balance in these ecosystems is the concurrent release of nitrogen (N), the element most likely to limit plant productivity. Release of N at or after thaw could increase plant N availability, stimulate plant C uptake and offset or balance permafrost C emissions. Although scientists acknowledge the key role N is likely to play in the permafrost C feedback to climate, there have been few empirical studies of the factors that control its fate in warming permafrost ecosystems. The objective of this project is to develop a mechanistic understanding of the role of permafrost N in the C balance of Alaskan tundra landscapes underlain by permafrost soils. The project will focus on plant acquisition of permafrost N because in most N-limited terrestrial ecosystems, plant uptake is the dominant fate of N released by microbial processes. Plants depend on fungal partners to access N beyond the reach of roots, so this research will also focus on plant mycorrhizal status and fungal community composition to elucidate the role fungal symbionts play in plant N acquisition. Finally, other fates of permafrost N will be explored, including stasis and loss. Proposed research will explore three general questions: What is the potential for release of plant-available nitrogen from thawing permafrost soil organic matter; what proportion of N released deep in the soil profile, at the base of the active layer, is acquired by mycorrhizae and plants and what are the key biotic and abiotic factors that control acquisition; and how will permafrost thaw and N release affect net ecosystem carbon balance and net biogeochemical radiative forcing from permafrost thaw at local and regional scales? The research approach includes three elements: observations of plants, fungi and soils across a regional survey of upland tundra ecological landscape units on the North Slope of the Brooks Range, Alaska; occupying intensive research sites in cold and warm moist acidic tundra, where measurements of mycorrhizal fungi and plant N acquisition and N loss will be made within long-term warming experiments and well-characterized natural thaw gradients; and modeling and regional integration with a terrestrial biosphere model specifically developed to simulate C and N dynamics in high latitude systems. We quantified root depth and biomass profiles for tundra plants in tussock- and shrub-dominated tundra plot at Eight Mile Lake near Healy, Alaska. We measured %C, %N, d13C, and d15N of aboveground and belowground plant material 24 hours after the addition of 250 mg of isotopically labeled 98 atom percent ammonium chloride. We also measured active layer thickness and soil organic horizon thickness in each labeled plot.
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