0421178OberbauerThe world's tropical rain forests play a disproportionately large role in the global carbon budget. Their current and future carbon balance is poorly understood and remains controversial because of large gaps in our understanding of carbon cycling in this biome. To date relevant studies in these forests have largely been limited to few carbon fluxes that were followed for short periods. For no topical rain forest has there been a multi-year integrated study of multiple components of both aboveground and belowground carbon cycling and how they interact with and are controlled by water, nutrients, and climatic factors. This Biocomplexity project will address these knowledge gaps to bring understand of tropical forest carbon cycling to a new level.We will build on complementary on-going research in an exceptionally well-studied tropical rain forest (La Selva, Costa Rica) for a first-time integrated study of forest carbon, nutrient, and hydrological cycles. Our study will contrast the effects of different phases of the ENSO cycle and will compare stands across a broad range of soil fertility levels, thus representative of the fertility levels of many of the world's tropical forests. The broad range of expertise represented in our team - tropical forest ecology, plant ecophysiology, micrometeorology, forest biogeochemistry, forest hydrology, ecosystem modeling, remote sensing, invertebrate biology - will allow us to together address many interacting aspects of the carbon, nutrient, and water cycles in this forest. With complementary data from on-going studies at La Selva, this project will provide a more comprehensive analysis of the forest carbon budget than has been attained for any TRF. Because our studies will be continuous through almost three years and for some data sets build on long-term measurements, we will be able to study how inter-year variation in climatic factors such as temperature and rainfall affect the complex interactions and feedbacks among carbon, nutrients, and water in this ecosystem type. By studying all of these cycles in concert, through time, and across a strong gradient of soil fertility levels, we will be able to identify and quantify the complex constraints and feedbacks among all these co-varying processes. We will integrate our findings by developing from our data an empirically-based tropical rain forest version of the ecosystem process model CENTURY. We will use this model to develop a generalizable, predictive understanding of how TRF currently processes carbon, and TRF carbon balance is likely to respond to the on-going changes in climate.Broader impacts - Through a many-faceted education program, this project will convey both our research findings and the concepts of Biocomplexity, global change, and ecosystem science, to diverse levels of students decision-makers, and the general public. The research component of this project will provide outstanding opportunities for intensive research training by hands-on participation in interdisciplinary science in the tropics for a postdoctoral fellow, graduate students, numerous undergraduate assistants, and Costa Rican postgraduates and assistants. The project will be presented in the form of lectures, field problems/walks, and informal interactions to the thousands of undergraduate and graduate students in university-level field biology courses that visit the field site annually. We have partnered with Fairchild Tropical Botanic Garden and the Organization for Tropical Studies with outreach programs that will annually reach thousands of children, students and the general public, both in the U.S. and in Costa Rica. Public education components of the project target will raise awareness of the school children, their teachers, and the general public to the connectivity of water, carbon and nutrient processes in the tropics and how their effects can extend to the global scale.