PREDISPOSITION OF TREES BY AIR-POLLUTANTS TO LOW-TEMPERATURES AND MOISTURE STRESS

Air pollution can have direct effects on trees. It can cause visible i njury to foliage and a disruption of physiological processes, such as photosynthesis and carbon allocation, leading to losses in growth and productivity. This review suggests that of equal or greater importance is the potential of air pollutants to indirectly affect tree growth a nd vitality by predisposing them to injury from other abiotic and biot ic stresses. Predisposition by air pollutants can be the result of a d isruption in biochemical processes, such as enzyme activity or product ion, or physiological factors (e.g. stomatal closure, carbon allocatio n). Air pollutants such as SO2, O3 and acidic mists have been implicat ed as predisposing agents to two of the most important of these stress es: low temperature and soil moisture. Probable mechanisms, as well as implications of predicted changes in global climate will be discussed .