Application of selenium and silicon to alleviate short-term drought stress in French marigold (Tagetes patula L.) as a model plant species

Selenium (Se) and silicon (Si) are the beneficial elements that may significantly modify plants' tolerance to various types of biotic and abiotic stress. They may be particularly important due to the current climate changes. The aim of model experiments was to assess how selenium and silicon could alleviate short-term drought stress in French marigold (Tagetes patula L. "Pascal"). Tagetes plant species are economically important annual plants and are also very popular decorative flowering species in city parks due to its beautiful colored flowers and resistance on drought stress. Silicon was applied in the form of silica sol and choline-stabilized orthosilicic acid (ch-OSA). Selenium was applied in the form of sodium selenate (Na2SeO4). They were tested at the following concentrations (mg dm(-3) of NS): silica sol level I (23.25), level II (31.0); ch-OSA - level I (0.21), level II (0.63); and Se - level I (0.4), level II (0.8). The experiment showed that silicon had stimulating effect on the biometric parameters of control plants cultivated under an optimal water regime. When the plants treated with selenium were exposed to stress, the values of their biometric parameters were generally higher than in the plants treated with silicon. Both silicon and selenium significantly modified the gas exchange parameters. During the growing season, the net photosynthesis activity (P-N), stomatal conductance (g(s)), and transpiration rate (E) tended to decrease, but they increased significantly when selenium and silicon were applied. In general, the factors significantly modified the plants' content of macro- and micronutrients as well as the proportions between them. Both selenium and silicon alleviated the short-term drought stress in French marigolds as a model plant, but when silicon was applied, the positive effect was modified by the source and its concentration.