^ABSTRACT

Over the past half century thousands of research papers on plant responses to tropospheric ozone have been published in international journals. A fraction of these studies focussed on trees, and most often they only described growth effects and visible injury. This paper reviews physiological responses of trees to ozone and interactions with light, temperature, drought, exposure strategy, nutrients, plant age, genotype, Co₂, air pollution, and biotic conditions. We follow ozone from its uptake in leaves to its sites of injury inside the cells. The effects on membranes, antioxidants, ethylene, lipids, proteins, carbohydrates, hormones and metabolites are briefly reviewed, as is interactions with frost and visible structural changes. The review gives a schematic model for the interconnected effects of ozone on the cellular level in trees, and summarizes the evidence for ozone being harmful to forest health. A meta-analysis of published data points to physiology deciduous trees as more sensitive to ozone exposure than coniferous trees.