Diurnal and seasonal changes in sensitivity of plants to short exposures of hydrogen chloride gas

Increasing the concentration of hydrogen chloride (HCl) gas during single 20-min exposures from 13 to 27 mg m⁻³ significantly increased amounts of visible foliar injury recorded after 48 h on pinto beans and radishes. These two species were equally sensitive to HCl gas. Fumigations made between 08.00 and 14.00 h were more damaging than those made earlier or later in the day. No clear effect of season was noted although injury from fumigations made in August was greater than that occurring in February. In addition to being related to concentrations of HCl, amounts of foliar injury were positively correlated with ambient temperatures and amounts of light, these relationships possibly explaining the greater sensitivity of plants in the period 08.00–14.00 h.