CAREER: Ecosystem Responses to Rising CO2 and Climate Change:
Feedbacks through the nitrogen cycle
National Science Foundation, 1 July 2001 - 30 June 2006
Collaborators: Paul Dijkstra, Yiqi Luo, Chris Field
Project Summary: Rising atmospheric CO2 and global warming could alter the functioning of terrestrial ecosystems, and a number of experiments have already been established to document these potential changes. These experiments have demonstrated some broad similarities among different ecosystems in their above-ground responses to these global changes, but whether biogeochemical responses below-ground exhibit predictable patterns is largely unknown. For example, elevated CO2 and warming can alter nitrogen availability to plants and nitrogen inputs to and losses from ecosystems, but results to date are equivocal, with empirical support for both increases and decreases in nitrogen availability. However, because of the short time scale of empirical studies to date and the different methods used, contrasting results can not be compared with confidence.
The proposed work will examine how elevated CO2 and warming alter nitrogen cycling in a broad array of terrestrial ecosystems, and how these changes will feed back to affect plant and ecosystem productivity. The research component of this CAREER proposal comprises: 1) N cycling measurements in CO2 and climate change experiments, 2) controlled greenhouse experiments, and 3) integration through modeling. The field experiments will document changes in N cycling in response to increased temperature and elevated CO2 using a long-term 15N tracer technique that will reveal time-integrated effects of these global changes on N cycling. The greenhouse study will explicitly determine the relative importance CO2- and warming-induced changes in soil water content for specific processes in the N cycle, providing a mechanistic underpinning to the field studies. The modeling integration will explore the consequences for longer-term ecosystem responses.
This research complements the proposed CAREER teaching and outreach activities. Observations and experiments (including those proposed here) along a 3000-m elevational gradient near Northern Arizona University will serve as the foundation for inquiry-based laboratories for courses in Ecosystem Ecology and Microbial Ecology. By drawing on publicity surrounding global change and by providing a scientific foundation for understanding these topics, these activities are designed to better engage undergraduate students in the process of science. This career plan brings together the PI’s interests in global change research and science education. The research extends past work on elevated CO2 and carbon and nitrogen cycling and helps outline a broader long-term objective: to understand how interactions among element cycles (here, C, N, and H2O) influence ecosystem processes, including responses to global change. The proposed teaching activities are designed to place results from this research – and the research process itself – in a broader context accessible to the public.