ASSESSMENT OF EDU STEM INJECTIONS AS A TECHNIQUE TO INVESTIGATE THE RESPONSE OF TREES TO AMBIENT OZONE IN-FIELD CONDITIONS

The study of the effects of ambient air pollution on trees suffers fro m some practical difficulties. One of these is the limited space gener ally available in fumigation chambers in both the field and laboratory , which makes investigations on large trees extremely difficult. There is thus a need to develop experimental techniques which do not rely o n fumigation chambers. In this paper we present the results of experim ents aimed at evaluating the response of fast growing trees to ambient ozone by means of antioxidant stem injections. Tests were performed i n greenhouse chambers and in the open field. Two clones of hybrid popl ar were used: Populus X euramericana I-214' and Populus deltoides X ma ximowiczii 'Eridano'. In a greenhouse chamber experiment, 80-day-old ( 40-60 cm) plants of 'I-214' and 'Eridano' were injected with either wa ter or a solution of N-[2-(oxo-1-imidazolidinyl)ethyl]-N' phenylurea ( ethylene diurea; EDU) and exposed to 85 nl l(-1) O-3 for 8 h day(-1). The plants injected with EDU were significantly less injured than the water-injected controls. The foliar symptoms caused by O-3 fumigation of 'Eridano' were similar to those that this clone often shows under f ield conditions in the Po plain (interveinal brown stipples on the upp er surface). The field experiment was performed at a rural location in the Po plain, northern Italy. Cuttings of both clones were planted in the ground in spring 1991. Every 2 or 3 weeks during summer for the f ollowing 2 years the plants were injected with either EDU solution or water. Leaf injury, gas exchange, chlorophyll content and increase in height and diameter were periodically assessed. At final harvest the a boveground biomass was measured. The results showed significantly less O-3 injury to the EDU-injected plants; they maintained their leaves f or longer than the control and with higher chlorophyll content. Howeve r, no significant effects of the treatment on leaf gas exchange or on height and diameter growth were detected. The significance of these re sults in relation to the effectiveness of EDU application for assessme nt of ambient O-3 effects on trees is discussed.