Considerations for establishing relationships between ambient ozone (O<SUB>3</SUB>) and adverse crop response

Abstract

Exposures to the all pervasive ambient ozone (O3) can and has resulted in visible foliar injury and (or) reduction of crop growth and yield. However, most of our knowledge regarding the latter effect is derived from above ambient, artificial O3 fumigations in field exposure chambers. In the most recent years, such methodologies have been the subject of much criticism. Further, in such studies, efforts to establish cause-effect relationships have mainly relied on the use of single-point, season-end statistical descriptors of the O3 exposure and crop yield measurements. Such models do not consider the time lag in feedback and the extent of plant stress, repair, or compensation that regulate the final crop biomass in response to highly variable ambient O3 exposures in time and space. Therefore, no single such model has performed consistently. In this paper we provide explanations for the problem. Further, we discuss the need to couple atmospheric properties that are conducive for the transfer of O3 onto plant canopies and crop properties that promote O3 uptake (absorbed dose), a prerequisite to the observed effect. Additional discussion is directed to considerations for performing experiments in chamberless, ambient environments and for the use of multipoint exposure-response models. Issues are highlighted as to the difficulties and uncertainties associated with the available data in establishing ambient air quality regulations to protect crops.