Persistent effects of short-term, high exposure to chlorine gas on physiology and growth of Pinus ponderosa and Pseudotsuga menziesii

Following a single acute exposure to chlorine gas, persistent effects on epicuticular waxes, cuticular transpiration, tree growth and mortality were studied in foliage of Pinus ponderosa and Pseudotsuga menziesii for three growing seasons. Chlorine gas exposure caused foliar injury to both exposed foliage and foliage that flushed after exposure (P < 0.05). The tendency to form films of water rather than droplets was greater in directly exposed foliage (P < 0.001). Rates of cuticular transpiration were higher for directly and indirectly exposed foliage of Pinus ponderosa up to 1 year after exposure and up to 6 months after exposure for directly exposed Pseudotsuga menziesii (P < 0.001), after which P. menziesii needles defoliated. Total water content (TWC) and relative water content were significantly correlated with foliar injury (P < 0.05). TWC was lower for directly exposed foliage up to 1 year after exposure (P < 0.001). There was no persistent negative effect on F-v/F-m ratios after 1 year. Exposure to chlorine gas did not affect needle length or annual shoot increment growth, but exposure was correlated with increased bud production. Needle longevity of foliage that flushed 2 months after exposure was reduced significantly (P < 0.001). Annual stem increment growth for both species decreased over at least three growing seasons following chlorine gas exposure (P < 0.001), and depended on distance from the spill site. Cone production was lower for exposed Pinus ponderosa trees compared to controls (P < 0.05), and tree mortality was higher within approx. 50 m of the release site for Pseudotsuga menziesii. Growth responses for both conifers agreed well with predicted patterns of carbon allocation after defoliation caused by chlorine gas exposure. (C) 2001 Annals of Botany Company.