Wednesday, August 14, 2019: 9:00 AM
M103, Kentucky International Convention Center
Rebecca E. Hewitt1, Hélène Genet2, D. Lee Taylor3, David McGuire2, Heaher Greaves2, Ruth Rutter2 and Michelle Mack1, (1)Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, (2)Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, (3)Department of Biology, University of New Mexico, Albuquerque, NM
Background/Question/Methods The release of permafrost-derived nitrogen (N) has the potential to fertilize tundra vegetation, modulate plant competition, stimulate productivity, and offset carbon (C) losses from thawing permafrost. To test if Arctic plants can access deep permafrost-derived N, we characterized rooting profiles and quantified acquisition of 15N tracer applied at the top of the permafrost table in moist acidic tundra subjected to almost three decades of experimental warming at Toolik Lake, Alaska. We harvested roots by depth increment down to the top of the permafrost table in ambient and warmed plots. The importance of belowground root traits to deep N acquisition was represented in a process-based ecosystem model by implementing a dynamic rooting profile, which allowed for the vertical distribution of root biomass as a function of aboveground biomass, vegetation productivity and relative depth to the thaw front, and a dynamic, vertically stratified soil N profile. Furthermore, modeling the release of newly thawed permafrost N was enhanced by improving the capacity of the model to represent spatio-temporal dynamics of soil temperature, soil moisture, and thaw depth, which are major drivers of soil biogeochemical cycles.
Results/Conclusions
The average thaw depth in warmed plots was 17 cm deeper than in ambient plots. The maximum rooting depth of forbs, sedges, and deciduous shrubs all showed a plastic response to increasing thaw depth as a result of warming. Across treatments, the deepest rooting species was the forb Rubus chamaemorus followed by the sedge Eriophorum vaginatum. The most deeply rooted species showed the greatest uptake of tracer after 24 hours. Root traits related to proximity of the deeply applied tracer had the strongest relationship to plant isotope acquisition. Implementation of species-specific dynamic rooting profiles and improvement of soil N and environmental dynamics increased the capacity of the ecosystem model to reproduce the observed effect of warming on changes in vegetation composition and productivity. Next, we will test the capacity of the improved model to represent spatial variability of above and belowground vegetation biomass and productivity and C and N pools and fluxes in reference to species-specific observations of above and belowground biomass collected across the North Slope of Alaska. We will then run model simulations across Arctic Alaska to assess the effect of deep N acquisition on the regional C balance and its feedback to climate.
