1. Nitrogen Limitation and Terrestrial C Storage Adrien C. Finzi Boston University afinzi@bu.edu Christine L. Goodale Cornell University clg33@cornell.edu NACP Meeting San Diego CA February 17-20 2009 30 Participants

2. Cramer et al. (2001) DGVM Hungate et al. (2003) C x N Interactions A Missing Component of the Predicted Terrestrial-C Sink

3. N limitation constrain ecosystem responses to elevated CO 2 ? a continuum of responses POP-EUROFACE Rhinelander ORNL Duke SETRES, SC Costal Plain slow or no loss of stimulation rapid loss or no stimulation Texas Tunnel Minnesota BioCON Florida Scrub Oak Flakaliden, Boreal Sweden Can the current generation of ecosystem models accurately represent the variation in response for the right reasons?

4. atmospheric N deposition may reduce N limitation to terrestrial C uptake effects are disputed holland et al., 2005, ecol. appl.

5. what is the relationship between atmospheric N deposition and primary production? magnani et al., 2007, nature nadelhoffer et al. 1996, nature

6. Science Challenges: 1.Limited (but growing) engagement of the C cycle science community A. stoichiometric constraints B. developing models of belowground dynamics i. N supply not solely a function of climate ii. belowground C allocation drives N cycling 1.Limited (but growing) engagement of the C cycle science community A. stoichiometric constraints B. developing models of belowground dynamics i. N supply not solely a function of climate ii. belowground C allocation drives N cycling 2.No real time or automated measurements of N cycling variables (except remotely sensed foliar [N]) 3.Resource intensive measurements (time & money) limit spatial and temporal extent of available data 4.Significant uncertainties in the effects of N deposition on NEP

7. Agenda Item for NACP Community Explicitly incorporate the biogeochemical cycle of N into discussions and measurements of the terrestrial C cycle 1.Development of databases for model development and calibration 2.Model-data intercomparison activities use existing, detailed experiments to test model C-N interactions - 15N tracer experiments to model dynamics of N dep. correctly - LIDET studies to assess model N mineralization dynamics 3.Develop standard measurements of N pools at carbon observation sites A. Foliar N at existing sites -spectral methods for high frequency measurements on time scales comparable with C flux measurements B. Leverage existing biometric measurements by sending samples for C & N analysis 4.Develop next-generation C-N experiments to aid model development