Differential ozone-induced alterations in the photosynthetic apparatus and chlorophyll fluorescence dynamics of two pea cultivars (Pisum sativum L.)

The phytotoxic nature of tropospheric ozone (O3) has led to substantial declines in global crop productivity. Given their nutritional richness, legumes serve as vital dietary staples, valued for their high protein, oil, and fiber content. A field experiment was conducted to assess the physiological plasticity of two pea (Pisum sativum L.) cultivars, K Agaiti (O3-sensitive) and K Damini (O3-tolerant), under elevated O3 (ambient + 15 ppb). The Ball-Woodrow-Berry (BWB) model revealed a greater change in the intercept for K Agaiti compared to K Damini, indicating stronger stomatal disruption. Analysis of net CO2 assimilation rate, A, versus calculated internal CO2 concentrations, Ci (A/Ci), and photosynthetic active radiation, Q (A/Q), curves and chlorophyll fluorescence transients demonstrated cultivar-specific variations in both light and dark reactions. K Agaiti exhibited significant photosystem II impairment, whereas K Damini showed moderate reductions linked to feedback inhibition of dark reactions. Vcmax of elevated O3-exposed plants decreased by 3.5% and 7.35% at the vegetative stage, and by 4.91% and 8.45% at the reproductive stage in K Damini and K Agaiti, respectively. Similarly, seed weight per plant declined by 2.55% in K Damini and 15.29% in K Agaiti. These findings highlight the resilience of K Damini's photosynthetic machinery under O3 stress, demonstrating cultivar-specific adaptability and providing insight into the physiological basis of ozone tolerance in pea.