Global environmental change is one of the most powerful forces regulating ecosystem services.  With rising concentrations of atmospheric CO2, our ability to understand and model the terrestrial carbon (C) sink has emerged as a central issue in the development of policies aimed at mitigating and adapting to climate change. In photosynthesis water is traded for carbon, and foliar nitrogen concentrations dictate the degree to which lost water results in fixed carbon; the biogeochemical cycles of water, carbon and nitrogen are inexorably linked.

The magnitude of the response of terrestrial ecosystems to rising concentrations of CO2 is varied in space and through time.  The diversity of these responses presents significant challenges on a conceptual (i.e., how can we explain this diversity) and modeling basis (i.e., can models predict the variability of ecosystem responses for the right reasons).  Because plants allocate resources to maximize carbon gain, carbon can be used as a common currency to understand the diversity of ecosystem responses to elevated CO2 and to develop a simple, explanatory model.
Results/Conclusions

Synthesizing information from the large number of single and multi-factor experimental manipulations with elevated CO2, this presentation will describe how plant maximization of C gain affects (1) belowground carbon allocation and the N cycle via interactions with the soil microbial community, (2) stomatal responses to elevated CO2 with cascading effects on the water and nitrogen cycles, and (3) the response of net ecosystem exchange to climate variability and the potential for nutrient feedbacks to long-term C uptake.