“…Among these secondary metabolites, phenolic compounds are of particular interest because of (i) their major ecological role in allelopathic processes (Haslam, 1989;Rhodes, 1994;Cooper-Driver and Bhattacharya, 1998), (ii) their role in the protection of plants against herbivores (Pisani and Distel, 1998) and (iii) their involvement in the response of plants to environmental stress such as intra and/or interspecific competition or atmospheric pollution (Muzika, 1993;Karolewski and Giertych, 1994;Peñ nuelas et al, 1996). Most bibliographical studies on the impact of atmospheric pollutants on phenolic compounds only concerns the impact of standard atmospheric pollutants under controlled experimental conditions (Karolewski, 1990;Giertych and Karolewski, 1993;Karolewski and Giertych, 1994;Peñ nuelas et al, 1996).…”