Submitted to: Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 1, 2002
Publication Date: December 6, 2002
Citation: Morgan, J.A. 2002. Looking beneath the surface. Science. 298:1903-1904. Interpretive Summary: Rising concentrations of atmospheric carbon dioxide have prompted the initiation of numerous studies designed to evaluate how higher carbon dioxide will affect important world ecosystems. Only a handful of long-term field studies have yet investigated the impact of rising carbon dioxide on unperturbed native ecosystems, and fewer yet have bothered to attack the difficult yet important issue of how rising carbon dioxide will influence important soil biological processes that ultimately determine the ability of ecosystems to respond to CO2. This review article discusses limitations in global change research that do not consider soil feedback mechanisms, and are therefore are unable to predict long-term responses of ecosystems to rising atmospheric CO2 and other global changes like temperature, precipitation and N deposition. The suggestion is made that well-integrated modeling/empirical field studies which are designed to evaluate critical knowledge gaps will be needed if we hope to be able to be able to predict long-term impacts of global climate change.
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 studies 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.