Ozone risk assessment of common cypress (Cupressus sempervirens L.) clones and effects of Seiridium cardinale infection

Cupressus sempervirens is a relevant species in the Mediterranean for its cultural, economic and landscape value. This species is threatened by Seiridium cardinale , the causal agent of the cypress canker disease (CCD). The effects of biotic stressors on O 3 risk assessment are unknown and a comprehensive O 3 risk assessment in C. sempervirens is missing. To fill these gaps, two clones of C. sempervirens , one resistant (Clone R) and one susceptible to CCD (Clone S), were subjected to three levels of O 3 (Ambient Air - AA; 1.5 x AA; 2.0 x AA) for two consecutive years in an O 3 -free -air controlled exposure facility and artificially inoculated with S. cardinale . Both the exposure- (AOT40) and flux -based (PODy) indices were tested. We found that PODy performed better than AOT40 to assess O 3 effects on biomass and the critical level for a 4% biomass loss was 2.51 mmol/m 2 POD 2 . However, significant O 3 dose -response relationships were not found for the inoculated cypresses because the combination of middle level O 3 (1.5 x AA) and inoculation stimulated a biomass growth in Clone S as hormetic response. Moreover, we found a different inter -clonal response to both stressors with a statistically significant reduction of total and belowground biomass following O 3 , and lower root biomass in Clone S than in Clone R following pathogen infection. In summary, Clone R was more resistant to O 3 , and inoculation altered O 3 risk via an hormetic effect on biomass. These results warrant further studies on how biotic stressors affect O 3 responses and risk assessment. (c) 2024 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY -NC -ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )