Combined Use of 15N Natural Abundances and Tracers to Elucidate Above- and Belowground C and N Cycle Linkages during Forest Succession

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Re-growing forests across the North Temperate Zone presently remove about 15% of fossil fuel carbon dioxide (CO2) emissions. It is unclear, however, how long and to what extent these forests will continue to sequester CO2 and thereby offset a major fraction of human-derived CO2 emissions. Recent measurements suggest that, in contrast to the long-held idea that ecosystem CO2 uptake declines to zero over time, forests can continue storing carbon for centuries after establishment. For this to occur, nitrogen cycling patterns and rates must change as tree species composition of the forest shifts during succession. How this occurs is not well understood, however, so this project will investigate mechanisms by which nitrogen cycling influences carbon uptake. The research will be conducted using novel, multi-scale, stable nitrogen isotope approaches in a large-scale, bold, experimental forest setting in northern Michigan where losses of maturing, early successional tree species are being accelerated by stem girdling. Carbon uptake by the experimental forest is being compared to a nearby non-manipulated forest under separate funding. The NSF-supported research here focuses on nitrogen exchanges between late-successional tree species, their fungal symbionts and soils as they control forest carbon balances. Results will provide a more complete understanding of controls on forest growth across successional stages and will improve predictions of temperate forest CO2 uptake and carbon balances. The study will serve as a resource for 'Kindergarten-to-Gray' environmental education and insights derived from this research will inform decisions of policymakers and resource managers regarding forest carbon sequestration and provision of ecosystem services.