The lichens Parmelia quercina, Parmelia sulcata, Evernia prunastri, Hypogymnia physodes, and Anaptychia ciliaris were exposed to ozone (O3) in controlled environment cuvettes designed to maintain the lichens at optimal physiological activity during exposure. Measurements of gas exchange, modulated chlorophyll (Chl) fluorescence, and pigment analysis were conducted before and after exposure to 300 mm3 (O3) m-3, 4 h per d for 14 d. No changes in the efficiency of photosystem 2 (PS2) photochemistry, the reduction state of QA, or the electron flow through PS2, measured by Chl fluorescence, were detected in any of the five lichen species studied. Additionally, neither photosynthetic CO2 assimilation nor xanthophyll cycle activity or photosynthetic pigment concentration were affected by high O3 concentrations. Thus the studied lichen species have significant capacities to withstand oxidative stresses induced by high concentration of O3. and A. Calatayud, P. J. Temple, E. Barreno.
Watermelon (Citrillus lanatus) plants were grown for two consecutive years in open-top chambers with three different ozone concentrations (O3-free air, O3 ambient, and air with additional O3; CFA, NFA, and NFA+O3) and three nitrogen fertilizer concentrations [0, 14.0, and 29.6 g N per pot; N0, N1, and N2). There was an interaction between ozone and N fertilizer for the major parameters studied. O3 and N2 treatments led to a significant decrease in maximum efficiency of photosystem 2 (PS2) photochemistry (Fv/Fm), and induced a significant decrease in the actual quantum yield of PS2 (ΦPS2), due mainly to the increased closure of PS2 reaction centres (qP) and to an increase in the non-photochemical quenching (NPQ). On the other hand, these plants exhibited an increased susceptibility to photoinhibition, which could be associated with an increased fraction of reduced QA. An increase in lipid peroxidation indicated that damage was occurring at the membrane levels. High N concentration enhanced the detrimental effects of ozone on the fluorescence parameter induction and lipid peroxidation. All these negative alterations led to a decreased yield. and A. Calatayud, F. Pomares, E. Barreno.