Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: June 21, 2003
Publication Date: September 15, 2005
Citation: Morgan, J.A. 2005. Rising atmospheric CO2 and climate change: Management implications for grazing lands. pp. 245-272. In: S.G. Reynolds and J. Frame (eds) Grasslands: Developments Opportunities Perspectives. FAO and Science Pub., Inc. Technical Abstract: It is widely accepted that the release of greenhouse gases into the atmosphere will have profound impacts on the earth’s climate, including global warming, altered precipitation patterns, and increased storm intensities. The predicted impact of global change is typically assessed by evaluating experiments conducted in various ecosystems subjected to one or at most two such environmental changes. However, the paucity of multiple-factor, multiple-year global change studies limits our understanding of how ecosystem processes will ultimately respond to multiple global changes. Recent multi-factor global change studies are an important step towards a more integrated approach to understanding multiple global changes, but at the same time results from some of these studie raises questions about our ability to design and interpret experiments for understanding long-term ecosystem responses to global change. One of the major challenges in interpreting field global change studies is understanding how soil nutrient cycle feedbacks can modulate or even change the direction of plant responses to global changes. For instance, litter from decaying plants and root exudates enter a large, diverse soil pool of unavailable nutrients that must be decomposed by microbes before being released back to plants. Some of these available nutrients may become immobilized by microbial growth; other nutrients may be rendered chemically or physically unavailable. Thus, the balance between nutrient release and immobilization processes determines the plant available nutrient status, and the ultimate plant response. While increases in atmospheric CO2 may initially stimulate photosynthesis and plant production, soil nutrient feedbacks resulting from more carbon substrates entering soil organic pools may constrain or eliminate that response. Our current knowledge of these processes is extremely limited, making long-term ecosystem responses to global change unreliable. To remedy this, future global change research needs to integrate simulation modeling with empirical field experimentation and target critical knowledge gaps, which can then be incorporated into appropriately designed models to evaluate long-term consequences of incremental global changes.