Gas exchange and JIP-test parameters of two Mediterranean maquis species are affected by sea spray and ozone interaction.

Mediterranean maquis coastal ecosystems are subject to multiple oxidative stresses of both natural and\r\nanthropic origin, as sea spray, drought, high irradiance and ozone. In this article it is hypothesized that\r\nthe interaction of ozone and sea spray is additive as a consequence of a higher reactive oxigen species\r\naccumulation. To test the hypothesis, an experiment was conducted in an Open Top Chambers facility\r\nwhere plants of Quercus ilex L. and Arbutus unedo L. were exposed to two levels of ozone and two levels of\r\nsea spray. The response of the species was evaluated by measurements of structural parameters (shoot\r\ngrowth and leaf biomass) and physiological parameters (leaf level gas exchange and chlorophyll a fluorescence).\r\nThe results contradict the hypothesis as the interaction of the two stresses is antagonistic on\r\nboth species. The structure of both species was negatively affected by sea spray, however the two stresses\r\ncombined allowed a higher growth and leaf area in A. unedo. The leaf level physiology of A. unedo was\r\nonly moderately affected by the two stresses alone and in combined, while that of Q. ilex was altered to a\r\nfurther extent by sea spray and by its combination with ozone: photosynthesis and efficiency of the PSII\r\nwas reduced by sea spray while the ratio of PSII to PSI was increased; the two stresses combined, instead,\r\ndecreased the PSII to PSI ratio allowing for a higher photosynthesis. It is concluded that A. unedo is more\r\nresistant than Q. ilex to the two stresses alone and in combination, that ozone and sea spray interact\r\nantagonistically, and that the activity of PSI has a key role in the stress response.