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Three-year-old red spruce seedlings were exposed to various concentrations of ozone, from 0.4 to 3 times ambient, for two consecutive growing seasons in open-top chambers in Ithaca, NY, USA. Exposures, which varied with changes in daylength, were from 30 May to 14 December l987 and 1 June to I December 1988. Seedling biomass, foliar pigments and carbohydrate content of roots and shoots were assessed once or twice per month. Tree biomass increased through the summer and declined slightly in late autumn, regardless of ozone treatment. Biomass and contents of sugar and starch of 1988 fixed growth declined linearly with exposure to increasing levels of ozone. Rates of decline in total shoot biomass and old shoot biomass increased linearly with exposure to increasing concentrations of ozone, but tree height was not affected. Seasonal means of starch content of roots decreased linearly with increasing doses of ozone, but in contrast seasonal mean sugar content and rate of sugar accumulation of roots increased linearly. Chlorophyll a and chlorophyll B contents were not affected by ozone. These data are consistent with the concept that ozone stress is cumulative, since effects on biomass and carbohydrate content of roots and shoots were not detected after the first year of exposure, but were detected after the second year of treatments. Furthermore, biomass was reduced by ozone only in tissues that were initiated during the first year of exposures and developed during the second year of exposures (1988 fixed growth). [ABSTRACT FROM AUTHOR]

Loblolly pine (Pinus taeda L.) seedlings from two families differing in ozone sensitivity, were exposed to ozone and acidic precipitation in modified open-top chambers, beginning in May of 1988. Visible injury (bleached needle tips) occurred after a late-season frost in April, 1989 on newly emerging (length ⩽ 5 cm) needles. After one week, needle tips turned brown and necrotic. Incidence of injury was recorded in April. May and June, 1989. Injury only occurred on trees exposed to ozone at above-ambient concentrations (1.7 and 2.5 × ambient), and was significantly greater in the ozone-sensitive family (GAKR 15-91) suggesting that this response is under some genetic control. Incidence of injury decreased with time and was more noticeable in the ozone-tolerant family (GAKR 15-23). There was no effect of acid rain, or interaction between ozone and acid rain, revealed by visible injury. In addition, experiments were conducted to determine if ozone and/or freezing temperatures enhanced electrolyte leakage. There were no differences observed in diffusate conductivity among treatments. These findings suggest that the observed injury was due to photo-oxidation induced by an ozone-low temperature interaction, and represent the first report of this type of injury in loblolly pine. [ABSTRACT FROM AUTHOR]

Two-year-old red spruce seedlings [Picea rubens Sarg. syn. P. rubra Du Roi) Link] were subjected to 6 simulated acid mist treatments (pH 2.5, 2.7, 3.0, 3.5, 4.0, 5.0) in a replicated experiment using open-top chambers. Acid mist solutions containing equimolar (NH4)2SO1 and HNO3 were applied twice weekly for 22 weeks, each application being equivalent to 2 mm of precipitation. Visible symptoms of foliar damage were observed on the 3 most acidic mist treatments (pH 2.5, 2.7, 3.0). The inputs of nitrogen, sulphur and acidity in the most acidic treatment were 55. 42, 1.3 kg ha¹ respectively, over a 10 week period. The plants subjected to the pH 2.5 treatment were found to be most severely damaged with approximately 40% foliar necrosis after 10 weeks of treatment. On approximately 80% of seedlings, necrosis was confined to current year needles only. These damaged needles were initially light brown or light orange in colour turning a deeper red 3 to 5 weeks after initial necrosis. Percentage foliar damage was linearly related to concentration (of NH4-, NO3, SO1² and H-) with 62% foliar damage in the pH 2.5 treatment after a 22-week period. Spray application stopped in December 1987. Observations during the following spring showed that the pH 2.5 and pH 3 treatments induced earlier flushing, requiring 60 day °C less thermal time than the pH 5.0 treatment. In 1988, this decrease in thermal requirement was equivalent to flushing 11 days earlier. There was no evidence of acid mist treatments inducing bud mortality. [ABSTRACT FROM AUTHOR]

Seedlings of red spruce [Picea rubens Sarg. syn. P. rubra (Du Roi) Link] were exposed to mists containing equimolar (NH4)2 SO4 and HNO3 at pHs of 2.5, 2.7, 3.0, 3.5, 4.0 or 5.0. The mists were applied twice each week, amounting to 2 mm precipitation equivalent on each occasion, between July and December, to open-top chambers supplied with charcoal-filtered air. Frost hardiness of shoots excised from seedlings was determined on 6 occasions starting on 21 September, and was found to be strongly influenced by acid mist treatments, seedlings subject to the most acidic mists being the least frost hardy. On 21 September when the first sample was taken the lethal temperature for killing 50% of shoots (LT50) was - 11°C for the least acidic (pH 5.0) mist and -7 °C for the most acidic (pH 2.5). By 19 October, the LT50s of pH 5.0 and pH 2.5 mists were - 27 and - 15 °C respectively. All intermediate treatments ranked according to treatment concentration, with the smaller concentrations causing lower LT50 values. The treatment at pH 30 provided S and N inputs to the seedlings similar to those experienced by red spruce at elevations of about 1000 m in the southern Appalachians. At pH 3.0, the frost hardiness LT10 during October was typically 8 °C higher than the pH 5.0 treatment, leading to a significant increase in the probability of frost damage at the LT10 level in an average October. The proximity of minimum night temperatures during September to December to the LT10 temperatures of red spruce shoots receiving large inputs of SO4&sup2-;, NO3-, NH4+ and H+ suggests that decreases in frost hardiness caused by intercepted cloud water containing large concentrations of these ions may play a significant part in the observed decline at mountain-top locations. [ABSTRACT FROM AUTHOR]