Chlorophyll a fluorescence in saccharine sorghum irrigated with saline water

ABSTRACT Soil salinity directly affects plants, interfering in the emission of fluorescence, and promoting the degradation of photosynthetic pigments. Thus, estimating the damage to the photosynthetic apparatus caused by saline water is an important tool to detect abiotic stresses. For this purpose, sorghum plants were cultivated in a greenhouse and irrigated with two water sources (NaCl and salt mixture) with six levels of electrical conductivity (EC) (0, 2.5, 5, 7.5, 10, and 12.5 dS m-1), forming a 6 × 2 factorial in randomized blocks with four repetitions. At 60 days after sowing, the photosynthetic pigments were quantified, the chlorophyll a fluorescence parameters (initial fluorescence [F0]; variable fluorescence [Fv]; maximum fluorescence [Fm]; quantum efficiency of photosystem II - PSII [Fv/Fm]; electron flux per reaction center [ET0/CR]; quantum energy dissipation [DI0/CR] and quantum yield for heat dissipation [φD0]) were evaluated. The photosynthetic pigments were decreased with an increase in the salinity of the irrigation water, and were more expressive at higher electrical conductivities. With the wear on the photosynthetic apparatus by the increase in salinity, a reduction in the emission of the chlorophyll a fluorescence was observed, pointing to a possible photoinhibition of photosystem II.