Global Change and the Carbon Balance of Arctic Ecosystems: The Importance of Carbon/Nutrient Interactions

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The Subject of this research is the role of carbon/nutrient interactions as constraints on carbon cycling processes and overall carbon budgets of terrestrial ecosystems. The specific focus is on carbon/nutrient interactions in three contrasting tundra ecosystems along a continuum from dry uplands to wet lowlands in northern Alaska. The research is placed in the context of global warming, viewing the predicted global temperature increase as an experiment in carbon/nutrient interactions at the ecosystem level. The central idea is that primary production of arctic ecosystem is strongly nutrient-limited, and thus its ability to respond to higher temperatures is constrained by nutrient supply. Soil respiration, on the other hand, is more directly limited by low soil temperature, as is the mineralization of nutrients in soil organic matter. Plant carbon gains associated with increased nutrient mineralization must thus be balanced against soil carbon losses due to increased soil respiration. To understand controls on carbon balance at the ecosystem level, one needs to understand controls on plant carbon/nutrient ratios and the ratio of soil carbon respiration to N and P mineralization. A program of research is proposed that includes process studies, whole- ecosystem experiments, and simulation modeling. The process studies are designed to improve understanding of C/N/P interactions at key points in the cycle of organic matter in terrestrial ecosystems, with a particular focus on the balance of soil respiration and N and P mineralization. The whole- ecosystem experiments are focused on determining correlations between changes in the C:N:P ratios of the major organic matter fluxes and organic matter pools. The modeling efforts are designed to help explain these correlated changes in whole ecosystems, to identify cause-effect relationships, and to clarify constraints on the observed range of variation in C:N:P ratios.