Effects of Nighttime Ozone Treatment at Ambient Concentrations on Sensitive and Resistant Snap Bean Genotypes

Abstract

The effect of nighttime ozone (O3) exposure, alone and in combination with daytime O3 treatment, was tested on yield of an O3-resistant (R123) and an O3-sensitive (S156) snap bean (Phaseolus vulgaris L.) genotype. Three trials, with exposure durations ranging in length from 14 to 21 days, were conducted in continuous stirred tank reactors located within a greenhouse. The effects of day-only (0800–1900 hr = 11 hours·day−1) and day + night (0800–1900 hr + 2000–0700 hr = 22 hours·day−1) exposure timings were compared. The Fall 2014 trial also tested the effect of nighttime-only (2000–0700 hr = 11 hours·day−1) O3 exposure. Nighttime O3 exposure alone, at 62 ppb, did not cause foliar injury and had no effect on the yield of either genotype. In combination with daytime O3 exposure, nighttime O3 concentrations up to 78 ppb did not impact yields or show a consistent effect on nocturnal stomatal conductance (gsn). When data were pooled across the day and day + night exposures times, mean daytime O3 levels ≥62 ppb caused foliar injury and significant yield decreases in all three trials. Under control conditions, R123 and S156 produced similar pod masses in two of the three trials. In all three trials, R123 produced significantly greater yields by mass than S156 with elevated O3. Nighttime conductance measurements suggested that S156 and R123 have inherently different gsn rates and that cumulative O3 exposure can increase gsn in both genotypes.