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United States Department of Agriculture

Agricultural Research Service

Title: The challenge of making ozone risk assessment more mechanistic for forest trees

Authors
item Matyssek, R - UNIVERSITAT MUNCHEN
item Sandermann, H - ECOTOX
item Wieser, G - FED RES & TRG CTR/FORESTS
item Booker, Fitzgerald
item Cieslik, S - INSTITUTE ENVIR & SUSTAIN
item Musselman, R - US FOREST SERVICE
item Ernst, D - GSF-FORSCHUNGSZENTRUM

Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 28, 2008
Publication Date: November 17, 2008
Repository URL: http://hdl.handle.net/10113/23602
Citation: Matyssek, R., Sandermann, H., Wieser, G., Booker, F.L., Cieslik, S., Musselman, R., Ernst, D. 2008. The challenge of making ozone risk assessment more mechanistic for forest trees. Environmental Pollution. 156:567-582.

Interpretive Summary: During the upcoming decades, atmospheric carbon dioxide and air pollutant ozone concentrations are likely to increase. The latter constitutes a risk for vegetation, including forest ecosystems, and detracts from the growth-stimulating effects of elevated carbon dioxide on plants. Thus, the need increases for reliable cause-effect related methodologies for ozone risk assessment. Although this assessment is improved when based on ozone uptake by plants rather than by ambient air ozone concentrations alone, ozone impacts are co-determined by the sensitivity per unit of ozone uptake, i.e. the physiologically effective ozone dose. This paper discusses the state of knowledge on the molecular and metabolic control of the effective ozone dose, and recent advances in assessing ozone uptake at the whole-tree and stand level. For example, derivation of ozone influx via measurements of leaf-level gas exchange provides a basis for using sap flow measurement in tree trunks to assess stomatal ozone uptake by the whole-tree and enables for up-scaling to the stand level. In concert, the eddy covariance approach provides whole-stand ozone flux estimates. In this way, new, complementary methods become available for validating and promoting modelling approaches in flux-based ozone risk assessment. Regarding the effective ozone dose, mechanisms that control the response of plant species and genotypes per unit of ozone uptake are discussed. The underlying detoxification, toxification, stress amplification and signalling events are considered, so that plant responsiveness parameters can be added to ozone flux models. Both ozone uptake and sensitivity per unit uptake need to be understood mechanistically and linked to each other through combined sapflow/eddy covariance and various ozone fumigation approaches, respectively, as a pre-requisite of approximations towards model development and routine application. Under progressing climate change, only a mechanistic understanding of ozone risk will be able to respond to an increasing demand for reliable and scientifically sound assessment methodologies.

Technical Abstract: In the upcoming decades, the earth’s atmosphere will contain increasing levels of carbon dioxide and possibly tropospheric ozone. The latter constitute a risk for vegetation, including forest ecosystems, counteracting the ability to sequester carbon. In view of climate change, the need increases for reliable cause-effect related methodologies for ozone risk assessment. Although this assessment can be improved when based on ozone uptake by plants, plant damage is co-determined by the sensitivity per unit of ozone uptake, i.e. the (physiologically) effective ozone dose. This paper discusses the state of knowledge on the molecular and metabolic control of the effective ozone dose, and recent advances in assessing ozone uptake at the whole-tree and stand level through empirical approaches. Derivation of ozone influx via stomata from leaf-level gas exchange sets the stage for introducing sap flow measurement in tree trunks to assess stomatal ozone uptake at the whole-tree and enable for up-scaling to the stand level. The eddy covariance approach is highlighted for its capacity to provide whole-stand ozone flux so that comparison with the sap flow approach can empirically yield non-stomatal ozone deposition at the stand level. In this way, new perspectives become available for validating and promoting modelling approaches in flux-based ozone risk assessment. Regarding the effective ozone dose, mechanisms are addressed that control the responses of plant species and genotypes. The underlying detoxification, toxification, stress amplification and signalling events are considered, so that plant responsiveness parameters can be added to ozone flux models. Both ozone uptake and sensitivity per unit uptake need to be understood mechanistically and linked to each other as a pre-requisite of approximations towards model development and routine application. Under progressing climate change, a mechanistic understanding of ozone risk will be able to respond to an increasing demand for reliable and scientifically sound assessment methodologies.

Last Modified: 9/29/2014
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