Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 26, 2005
Publication Date: July 12, 2005
Citation: Fiscus, E.L., Booker, F.L., Burkey, K.O. 2005. Crop responses to ozone: uptake, modes of action,carbon assimilation and partitioning. Plant Cell and Environment. 28:997-1011. Interpretive Summary: Recent advances in understanding the mechanisms of ozone damage to crops and its impact on productivity are discussed. The initial event is the entry of ozone into the leaf where a series of damage and detoxification reactions may occur. Either or both of these are thought to trigger alterations in plant behavior leading to decreased photosynthesis, additional resource losses incurred as repair and protection costs and lowered productivity. Real time assessment of crop losses due to ozone is a difficult task but advances are being made in this area as well by turning to crop loss models based on ozone entry into the leaf and incorporating the influence of real time meteorological data on this process. Current methods are based simply on daily average concentrations in the air or at most incorporate some concentration damage threshold value or weighting function. Individual species or cultivars are more or less resistant to ozone damage and understanding this genetic component will increase the reliability with which we can predict crop losses and lead to development of more damage resistant plants with little cost in productivity.
Technical Abstract: The inhibitory effects of tropospheric O3 on crop photosynthesis, growth, and yield have been documented in numerous studies over the past 35 years. In large part, the results of this research supported governmental regulations designed to limit tropospheric O3 levels to concentrations that affected crop production at economically acceptable levels. Recent studies have brought into question the efficacy of these concentration-based O3 standards compared with flux-based approaches that incorporate O3 uptake along with environmental and biotic factors that influence plant responses. In addition, recent studies provide insight into the biochemical mechanisms of O3 injury to plants. Current interpretations suggest that O3 rapidly reacts with cellular components upon entry into the leaf intercellular space which initiates a complex set of responses involving the formation of toxic metabolites and generation of plant defense responses that are met with variably effective countermeasures. Plant species and cultivars exhibit a range of sensitivity to O3, evident as heritable characteristics, that must reflect identifiable biochemical and molecular processes that affect sensitivity to O3 injury, although understanding of their exact makeup remains incomplete. Ozone clearly impairs photosynthetic gas-exchange processes, which might include effects on electron transport and guard cell homeostasis as well as the better-documented effects on carbon fixation via decreased Rubisco activity. Translocation of photosynthate might be inhibited by O3 exposure as well. Further, the influence of tropospheric O3 needs to be considered when assessing potential effects of rising concentrations of atmospheric CO2 on crop production. Advances in O3 flux modeling and improved understanding of biochemical and molecular effects of O3 on photosynthetic gas-exchange and plant-defense processes are leading to more-complete, integrated assessments of O3 impacts on crop physiology that continue to support rationale for maintaining or improving current O3 air quality standards.