Relationship between leaf life-span and photosynthetic activity of Quercusilex in polluted urban areas (Rome)

Anatomical, morphological and physiological leaf traits of Quercus ilex in response to different traffic levels (high traffic level, type A sites; ave rage traffic level, type B sites; control sites, type C sites) were analyse d in Rome. Superficial leaf deposits were analysed comparing unwashed and w ashed leaf samples. Washing lowered Pb 61% in A, 54% in B and 27% in C. Sr, Fe, Cu, Zn and Al showed the same trend as Pb. The higher photosynthetic a ctivity of 1-year-old leaves (Pn = 7.0 +/- 2.9 mu mol m(-2) s(-1), average value) in A sites with respect to B sites (6.7 +/- 2.4 mu mol m(-2) s(-1)) and C sites (6.7 +/- 1.8 mu mol m(-2) s(-1)) seems to be related to higher stomatal conductance (g(s) = 0.13 +/- 0.06 mol m(-2) s(-1)), higher total c hlorophyll content (Chl = 1.57 mg g(-1)) and higher leaf thickness (L-T = 2 18.9 mu m), particularly palisade parenchyma thickness (109.4 mu m) Q. ilex showed, on average, 95% of 1-year-old leaves and rarely 2-year-old leaves in A and B sites; 77% 1-year leaves, 20% previous-year leaves and sporadic 3-year leaves in C sites. The enhanced leaf senescence in A sites is compen sated by a stimulated shoot production (18% higher with respect to C sites) ; 25% increased specific leaf area seems to be compensatory growth occurrin g in order to increase the size of the assimilatory area. The inverse trend of leaf life-span and Pn seems to be Q. ilex' adaptive strategy in pollute d areas. (C) 2000 Elsevier Science Ltd. All rights reserved.