Demonstration of a diel trend in sensitivity of Gossypium to ozone: a step toward relating O3 injury to exposure or flux

Abstract

Plant injury by ozone (O3) occurs in three stages, O3 entrance through stomata, overcoming defences, and attack on bioreceptors. Concentration, deposition, and uptake of O3 are accessible by observation and modelling, while injury can be assessed visually or through remote sensing. However, the relationship between O3 metrics and injury is confounded by variation in sensitivity to O3. Sensitivity weighting parameters have previously been assigned to different plant functional types and growth stages, or by differentially weighting O3 concentrations, but diel and seasonal variability have not been addressed. Here a plant sensitivity parameter (S) is introduced, relating injury to O3 dose (uptake) using three independent injury endpoints in the crop species, Pima cotton (Gossypium barbadense). The diel variability of S was determined by assessment at 2h intervals. Pulses of O3 (15min) were used to assess passive (constitutive) defence mechanisms and dose was used rather than concentration to avoid genetic or environmental effects on stomatal regulation. A clear diel trend in S was apparent, with maximal sensitivity in mid-afternoon, not closely related to gas exchange, whole leaf ascorbate, or total antioxidant capacity. This physiologically based sensitivity parameter provides a novel weighting factor to improve modelled relationships between either flux or exposure to O3, and O3 impacts. This represents a substantial improvement over concentration- or phenology-based weighting factors currently in use. Future research will be required to characterize the variability and metabolic drivers of diel changes in S, and the performance of this parameter in prediction of O3 injury.

Diurnal variation of apoplastic ascorbate in winter wheat leaves in relation to ozone detoxification

“…Growing attention has been paid to considering the combination of O 3 uptake and detoxification (Dizengremel et al, 2008;Fares et al, 2010;Grantz, 2014;Grantz et al, 2013;Heath et al, 2009;Musselman et al, 2006;Massman, 2004). Besides species and developmental stages, the detoxification processes to O 3 are theoretically dependent on temporal changes of O 3 concentration and other environmental conditions, such as solar radiation, air temperature and moisture stress (Heath et al, 2009).…”

Diel trend in plant sensitivity to ozone: Implications for exposure- and flux-based ozone metrics

“…In other cases the exposure-based metrics performed as well (Feng et al, 2012;Gonzalez-Fernandez et al, 2010;Karlsson et al, 2004). An empirically determined timecourse of a sensitivity factor, S, was recently obtained in Pima cotton (Gossypium barbadense; Grantz et al, 2013), allowing further investigation of the relationships among candidate O 3 metrics in contrasting environments.…”

“…Effective flux and effective dose are the values of F and D weighted by plant sensitivity to ozone (S; Grantz et al, 2013) as…”

“…Values of S were initially obtained from doseeresponse relationships between D and plant injury based on in situ digital photographic estimation of chlorosis and necrosis (Grantz et al, 2013). Photographic assessment of foliar injury was chosen for the present analysis as a well-established method to document and to confirm O 3 damage (Flagler, 1998).…”

“…a b s t r a c t Plant sensitivity to ozone (O 3 ) is critical to modeling impacts of air pollution on vegetation. A diel timecourse of sensitivity (S) was recently determined in Pima cotton (Grantz et al, 2013). The sensitivity parameter serves as a weighting factor for stomatal uptake (ozone flux, F), or cumulative F (dose, D).…”