MEMORY EFFECTS IN THE ACTION OF OZONE ON CONIFERS

Conifers are known to possess relative ozone tolerance in short-term e xperiments. A scenario for ozone damage of conifers is now derived fro m the first exposure experiments in which both the initial biochemical response phase and delayed visible symptom development were studied. A number of early biochemical ozone responses could be detected in Nor way spruce (Picea abies [L.] Karst.) and Scots pine (Pinus sylvestris L.). The stress metabolite catechin persisted over several months. In the year following ozone treatment of spruce, decreases in pigment con tent and photosynthetic capacity, as well as development of visible sy mptoms (chlorosis, banding), mere determined in the needle age classes previously exposed to an accumulated hourly ozone dose above 40 ppb ( AOT(40)) of greater than or equal to 60-80 ppm . h. The visible sympto ms developed during spring emergence of the new flush. In the case of Scots pine, an ozone dose (AOT(40)) of greater than or equal to 30 ppm . h caused the premature shedding of needles 9 months after treatment . The delayed symptoms of both spruce and pine occurred during known p hases of endogenous stress. The symptoms appeared to reflect an ozone ''memory'' imprinted by the induced early stress reactions. Ambient AO T(40) ozone doses in Central Europe are in the range 4 and 50 ppm . h per growing season. Ozone is proposed to potentially damage conifers t hrough memory effects (''abiotic'' pathway) or through predisposition for pathogen attack (''biotic'' pathway). (C) 1998 Academic Press