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COMPLEXITIES IN UNDERSTANDING ECOSYSTEM RESPONSE TO OZONE
Citation:
Andersen, C P. AND N. E. Grulke. COMPLEXITIES IN UNDERSTANDING ECOSYSTEM RESPONSE TO OZONE. HUMAN AND ECOLOGICAL RISK ASSESSMENT. Association for Environmental Health and Sciences, Amherst, MA, 7(5):1169-1182.
Description:
Ecological risk assessment of 03 impact requires consideration of many factors that, perhaps are not of concern in human health risk assessments. The episodic nature of 03 exposure, functional complexity of species assemblages, and the broad spatial and temporal scales characteristics of natural ecosystems make ecological risk assessment extremely difficult. The majority of exposure studies using plants have examined the sensitivity of individual species, growing under controlled conditions. Research has shown that individuals growing in plant mixtures may not respond the same way to 03 as when growing alone. In addition, other naturally stresses can modify plant response to 03. Understanding the effect of 03 on natural systems and protection vegetation resources represent significant scientific and regulatory challenges.
Here we review several factors that need to be considered when evaluating ecosystem response to 03. Then we briefly present two examples of controlled seedling studies that were conducting to better understand mechanisms of tree respnse to 03. In the first example controlled exposure studies revealed responses in tree roots that led to hypothesis testing in the field in ponderosa pine ecosystems. Field experiments have confirmed a similar response in root biomass and carbohydrates across a natural 03 gradient in S. California, suggesting at least a partial role for 03 in the response. The second example illustrates the difficulty of understanding mechanistic interactions to 03 stress even in controlled chamber studies. The second example also illustrates the difficulty of using chamber studies to understand responses in the field. While our knowledge of vegetation response to 03 is extensive and compelling, important questions remain about how to quantify these effects in the field, assess their magnitude, and establish a suitable standard that is protective of ecosystems.