The research proposed here utilizes annual grassland as a model system to test four hypotheses concerning the regulation of the cycles of carbon, nitrogen, and water in response to global change. Specifically, the PIs will explore the mechanisms through which (1) plant physiology and species dynamics alter cycles of C, N, and H2O, (2) levels and dynamics of C, N, and H2O regulate plant species composition, (3) microorganisms control short-term and long-term N availability, and (4) plant chemical composition regulates structure and function of the soil microbial community. Together, these hypotheses dissect the complex web of feedbacks linking biogeochemical cycles and ecological dynamics. The research builds on the infrastructure and ongoing operations of the Jasper Ridge Global Change Experiment, a multi-factor, ecosystem-scale manipulation. The manipulations were initiated in 1998 with NSF support and are now supported by the Packard Foundation. They include two levels of temperature, two of CO2, two of N deposition, and two of precipitation, with single-factor manipulations as well as all of the possible 2-way, 3-way, and 4-way combinations.
The team includes biogeochemists, ecophysiologists, population biologists, and microbial ecologists. The project will explore interactions between biogeochemical cycles and species dynamics across a range of time scales, from short-term physiological changes, through changes in species composition that unfold over several generations, to slow feedbacks from changes in soil stocks of C and N. The experiment's large array of treatments, plots that contain thousands of individuals of the dominant plants, and duration of several generations of the key species, provides a unique framework for addressing specific questions about biogeochemical responses to realistic global changes as well as fundamental questions about controls on major biogeochemical cycles. A modeling framework will be used that combines biogeochemistry, species changes, and species effects on biogeochemistry for synthesizing results across the project and integrating those results in the broader fabric of global-change research. This experiment is intended as a model system, where ease of manipulation and rapid responses can facilitate testing mechanistic hypotheses and establishing a framework for generalizing underlying principles to other ecosystems.
The proposed research will have a range of broader impacts. Jasper Ridge provides a core for diverse projects led by students as well as independently funded researchers. Located on university campus in a major urban area, the project is highly visible and widely integrated in Stanford classes as well as organized activities for K-12 students and the general public. It is an effective tool for communicating the nature of global changes, the diversity of their impacts, and the potential of biogeochemistry research. With the funding requested here, we will focus on increasing opportunities for secondary students, with an organized curriculum and internships.
