15 - Response of Stem Growth and Function to Air Pollution

Abstract

This chapter reviews the literature on the effects of several major types of air pollutants on stem growth and function, with the goal of better defining our knowledge in these areas and of suggesting areas in need of further investigation. The primary air pollutants of concern currently are ozone, acid deposition, and elevated CO2. Heavy metals are primarily of concern near emission sources. The effect of air pollutants on plants depend on the pollutant, the exposure pattern, and the site of absorption. In Europe, a decline in conifers has stimulated much research into the effects of air pollution on trees. Air pollution may affect annual growth rings through changes in ring width, element composition, or organic composition. Three types of data that have been collected using tree rings: ring width/basal area increment; isotopic composition; and density and chemical composition are examined. The response of forest trees to elevated CO2 exposure has been reviewed. Mechanistic models are not well developed for stem growth. There is ample evidence from chamber exposure studies that stem growth in young trees can be reduced by ozone and other pollutants. The mechanisms through which pollutants affect stem growth are likely to be as diverse as the pollutants.