The Impact of Abiotic Environmental Stressors on Fluorescence and Chlorophyll Content in Glycine max (L.) Merrill

In this study, we present the results of the impact of abiotic environmental (chemical) stressors in the soil environment (salinity, acidification, inorganic elements from industry—red mud waste containing Al) on the content and fluorescence of chlorophyll in the assimilating tissues of Glycine max (L.) Merrill, cv. ES Mentor. Under controlled conditions of a pot experiment during the 2023 growing season, we applied graded doses of these stressors (salinity—doses of 20, 30, and 60 g NaCl per 2 dm3 of water used for plant irrigation; acidity—pH 6, pH 5, and pH 4; red mud—200 g, 400 g, and 600 g per pot) and assessed their impact on the effective and maximum quantum yield of photosystem II (PSII), yield Y(II), or the ratio of variable to maximum fluorescence—the Fv/Fm test. These tests are used to detect plant stress. The Y(II) test yielded values in the range of 0.627–0.800. Significant differences (variance analysis, 95% Least Significant Difference—LSD, post hoc test of analysis of variance—ANOVA) in reducing PSII chlorophyll fluorescence (Y(II)) were found between the medium and high doses of all three stressors compared to the control, indicating plant stress response. The Fv/Fm test yielded values between 0.668 and 0.805 and similarly detected stress responses in plants to all medium and high doses of stressors. The evaluated cultivar showed tolerance to moderately increased salt (NaCl) content and red mud levels. This was also confirmed by the chlorophyll content expressed as the Chlorophyll Content Index (CCI). The highest (significantly confirmed) chlorophyll content was found in the control variant and the variants with lower salt content and a soil pH of 6, with values of 35.633–37.467 CCI, compared to variants with higher red mud content (15.533–18.133 CCI) and higher soil acidity with pH 4 (22.833 CCI). Based on the results obtained, we conclude that the ES Mentor cultivar is tolerant to lower doses of the assessed stressors and can be cultivated in agricultural practice. However, medium to high doses of stressors trigger a strong stress response in plants and, therefore, we do not recommend cultivating this variety in contaminated environments.