Gas exchange and chlorophyll fluorescence of pea (Pisum sativum L.) plants in response to ambient ozone at a rural site in Egypt

Egyptian pea cultivars (Pisum sativum L. cultivars Little Marvel, Perfection and Victory) grown in open-top chambers were exposed to either charcoal-filtered (FA) or non-filtered air (NF) for five consecutive years (2009–2013) at a rural site in northern Egypt. Net photosynthetic rates (P_N), stomatal conductance (g_s), intercellular CO₂ (C_i) and chlorophyll fluorescence were measured. Ozone (O₃) was found to be the most prevalent pollutant common at the rural site and is suspected to be involved in the alteration of the physiological parameters measured in the present investigation. P_N of different cultivars were found to respond similarly; decreases of 23, 29 and 39% were observed in the cultivars Perfection, Little Marvel and Victory, respectively (averaged over the five years) due to ambient O₃. The maximum impairment in P_N was recorded in the cultivar Victory (46%) in 2013 when the highest O₃ levels were recorded (90 nL L⁻¹). The average stomatal conductance decreased by 20 and 18% in the cultivars Little Marvel and Perfection, respectively, while the average stomatal conductance increased on average by 27% in the cultivar Victory. A significant correlation was found between P_N and C_i, indicating the importance of non-stomatal limitations of photosynthesis, especially in the cultivar Victory. The P_N vs. Ci curves were fitted to a non-rectangular hyperbolic model. The actual quantum yield (Φ_PSII) and photochemical quenching coefficient (qP) were significantly decreased in the leaves of plants exposed to NF air. Non-photochemical quenching (NPQ) was increased in all cultivars. Exposure to NF air caused reductions in chlorophyll (Chl a) of 19, 16 and 30% in the Little Marvel, Perfection and Victory cultivars, respectively. - Highlights: • Ozone (O₃) concentrations recorded were within the ranges of phytotoxicity. • O₃ has a clear influence on the physiological parameters. • O₃ decreased Photosynthetic rates, chlorophyll fluorescence parameters. • The variability in stomatal response may be due to inherent differences