An ozone-low temperature interaction in loblolly pine (<em>Pinus taeda</em> L.).

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 &les; 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]