An ozone‐low temperature interaction in loblolly pine (Pinus taedaL.)

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Abstract
SUMMARY: Loblolly pine (Pinus taedaL.) 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.