While existing observations suggest that arctic plant communities undergo dramatic changes in species composition, net primary productivity (NPP), and biomass in response to climate warming and subsequent increased soil nutrient mineralization, current models used to predict carbon (C) and nitrogen (N) cycling in arctic tundra are lacking inclusion of higher trophic levels and, thus, are missing mechanisms that may be having considerable effects. Funds are proided to concurrently measure plants, soil invertebrates and microbes (biomass and diversity) as they respond to increased soil nutrients to test ecological theory regarding such changes and understand feedbacks among trophic levels. The proposed work addresses whether we are witnessing simple increases and subtle shifts in the ecosystem components or fundamental changes in the ecosystem that have the potential to alter the current balance of biota, carbon and nitrogen.
Theory suggests that when NPP increases, additional trophic levels should enter the system because there is now enough energy to sustain them. These changes will be more dramatic in lower NPP systems, such as arctic tundra, because the dynamics are not linear. The study will examine how soil communities and nutrient cycling respond to changes in plant growth and how these responses compare between two common arctic ecosystems that differ in NPP, dry heath and moist acidic tussock tundra. It will use existing experimental plots of the Arctic LTER at Toolik Lake, Alaska to test these hypotheses at the plot scale under long-term nutrient enrichment and will establish new smaller-scale nutrient amendment experiments on which more localized and frequent plant and soil sampling will occur to capture a temporal and spatial scale more appropriate for soil organisms. Theoretical and empirically-based models will be used to aid in the analysis and interpretation.
