The tools that evaluate the salinity effects on plants have great relevance as they contribute to understanding of the mechanisms of tolerance. This study aimed to evaluate gas exchanges and the contents of photosynthetic pigments in bell peppers cultivated with saline solutions (0, 1, 3, 5, 7 and 9 dS m^-1) prepared using two sources: NaCl and a mixture of Ca, Mg, K, Na and Cl salts, in randomized blocks with a 6 x 2 factorial scheme and 4 replicates, totaling 48 experimental plots. The net photosynthesis (A), stomatal conductance (gs), transpiration (E), internal CO₂ concentration (Ci), instantaneous carboxylation efficiency (A/Ci) and water use efficiency (WUE), besides chlorophyll a, b and carotenoids were evaluated. The gas exchange parameters were efficient to indicate the effects of salinity. All photosynthetic pigments decreased with increased electrical conductivity, and the chlorophyll a is the most sensitive to salinity, while the water use efficiency increased with the increment of electrical conductivity.

FLUORESCÊNCIA DA CLOROFILA COMO INDICADOR DE ESTRESSE SALINO EM FEIJÃO CAUPI - DOI: 10.7127/rbai.v12n300700

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 [F_v]; maximum fluorescence [F_m]; quantum efficiency of photosystem II - PSII [F_v/F_m]; 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.