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Leaf Gas Exchange and Chlorophyll a Fluorescence in Wheat Plants Supplied with Silicon and Infected with Pyricularia oryzae

This study investigated the effect of silicon (Si) on the photosynthetic gas exchange parameters (net CO₂ assimilation rate [A], stomatal conductance to water vapor [g_s], internal CO₂ concentration [C_i], and transpiration rate [E]) and chlorophyll fluorescence a parameters (maximum quantum quenching [F_v/F_m and F_v′/F_m′], photochemical [q_P] and nonphotochemical [NPQ] quenching coefficients, and electron transport rate [ETR]) in wheat plants grown in a nutrient solution containing 0 mM (–Si) or 2 mM (+Si) Si and noninoculated or inoculated with Pyricularia oryzae. Blast severity decreased due to higher foliar Si concentration. For the inoculated +Si plants, A, g_s, and E were significantly higher in contrast to the inoculated –Si plants. For the inoculated +Si plants, significant differences of F_v/F_m between the –Si and +Si plants occurred at 48, 96, and 120 h after inoculation (hai) and at 72, 96, and 120 hai for F_v′/F_m′. The F_v/F_m and F_v′/F_m′, in addition to total chlorophyll concentration (a + b) and the chlorophyll a/b ratio, significantly decreased in the –Si plants compared with the +Si plants. Significant differences between the –Si and +Si inoculated plants occurred for q_P, NPQ, and ETR. The supply of Si contributed to decrease blast severity in addition to improving gas exchange performance and causing less dysfunction at the photochemical level.