Photosynthesis responses to ozone in young trees of three species with different sensitivities, in a 2-year open-top chamber experiment (Curno, Italy)

This paper reports the findings of an open-top chamber experiment carried out\r\nin northern Italy (Forest nursery at Curno), during the 2004 and 2005 growth\r\nseasons, on Fagus sylvatica and Quercus robur seedlings and on Populus nigra\r\ncuttings, in order to test their photosynthesis response to ambient ozone. The\r\nexperimental protocols were non-filtered air (NF), charcoal-filtered air (CF)\r\nand open air (OA). Tests performed included morphological features of leaves;\r\ndevelopment of foliar symptoms; chlorophyll content, determined by nondestructive\r\nmeans; chlorophyll fluorescence (direct fluorescence and JIP test)\r\nand gas exchanges and net photosynthesis (PN). Main findings were as follows:\r\n(1) symptoms occurred early and were extensive in P. nigra, and they occurred\r\nlater in F. sylvatica, whereas early degeneration of chlorophyll occurred in late\r\nsummer in Q. robur; (2) in conditions of ozone exposure, the three species\r\nall presented a decline in photosynthesis efficiency and a decrease in PN,\r\nregardless of the symptomatology they displayed; (3) leaf traits are predictors of\r\nspecies-specific sensitivity to ozone—the high density of Q. robur foliar tissues\r\nprevents this species from developing visible symptoms and reduces the extent\r\nof physiological responses and (4) physiological responses varied from year\r\nto year in the same species—responses were lower in the second year of the\r\nexperiment, when plants had become better acclimatized to plot conditions.