title: The harsh life of an urban tree: the effect of a single pulse of ozone in salt-stressed Quercus ilex saplings.
abstract: Ozone (O3) and salinity are usually tested as combined factors on plant performance. However, the response to a single episode of O3 in plants already stressed by an excess of NaCl as occurs in the natural environment has never been investigated, but is important given that it is commonly experienced in Mediterranean areas. Three-year-old Quercus ilex L. (holm oak) saplings were exposed to salinity (150 mM NaCl, 15 days), and the effect on photosynthesis, hydric relations and ion partitioning was evaluated (Experiment I). In Experiment II, salt-treated saplings were exposed to 80 nl l-1 of O3 for 5 h, which is a realistic dose in a Mediterranean environment. Gas exchanges, chlorophyll fluorescence and antioxidant systems were characterized to test whether the salt-induced stomatal closure limited O3 uptake and stress or whether the pollutant represents an additional stressor for plants. Salt-dependent stomatal closure depressed the photosynthetic process (-71.6% of light-saturated rate of photosynthesis (A380)) and strongly enhanced the dissipation of energy via the xanthophyll cycle. However, salt-treated plants had higher values of net assimilation rate/stomatal conductance (A/gs) than the controls, which was attributable to a greater mesophyll conductance gm/gs and carboxylation efficiency (higher gm/maximal rate of Rubisco carboxylation (Vcmax)), thus suggesting no damage to chloroplasts. O3 did not exacerbate the effect of salinity on photosynthesis, however a general enhancement of the Halliwell-Asada cycle was necessary to counteract the O3-triggered oxidative stress. Despite the 79.4% gs reduction in salt-stressed plants, which strongly limited the O3 uptake, a single peak in the air pollutant led to an additional burden for the antioxidant system when plants had been previously subjected to salinity.
authors: Department of Agriculture, Food and Environment, University of Pisa, Via del Borghetto, 80-56124 Pisa, Italy.
authors: Lucia
authors: L
authors: Guidi
authors: Damiano
authors: D
authors: Remorini
authors: Lorenzo
authors: L
authors: Cotrozzi
authors: Tommaso
authors: T
authors: Giordani
authors: Giacomo
authors: G
authors: Lorenzini
authors: Rossano
authors: R
authors: Massai
authors: Cristina
authors: C
authors: Nali
authors: Lucia
authors: L
authors: Natali
authors: Elisa
authors: E
authors: Pellegrini
authors: Alice
authors: A
authors: Trivellini
authors: Alberto
authors: A
authors: Vangelisti
authors: Paolo
authors: P
authors: Vernieri
authors: Marco
authors: M
authors: Landi
mesh_terms: D000975:Antioxidants / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D010126:Ozone / Q000633:toxicity*; D010788:Photosynthesis / Q000187:drug effects; D029963:Quercus / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D010126:Ozone
keywords: antioxidant system; photosynthesis; salinity; tropospheric ozone; urban environment