The effects of lithium chloride on seed germination, seedling growth and antioxidant response in Brassica oleracea var. capitata

Abstract

The widespread use of lithium (Li) in various industries, the low recycling rate of products with high Li content, and Li extraction and ore processing have resulted in Li becoming a contaminant of emerging concern with biological and ecological effects. Despite increased research over the past two decades, its influence on plants remains largely unknown and sometimes unclear. This study analyses the effects of elevated Li concentrations in the substrate (0–1000 mg kg-¹), added as LiCl, on Brassica oleracea var. capitata (cabbage) plants. We monitored the seed germination, seedling growth, nutrient status, photosynthetic pigment content, and antioxidant enzyme activities in plants grown hydroponically during two-week experiments. Lithium exhibited hormesis in some of the parameters analysed. The germination rate remained high (>80%) at all Li concentrations. In the earliest stages of plant growth, the lowest applied Li concentrations (25–100 mg L-¹) stimulated radicle elongation and root hair development, while higher concentrations caused their regression and led to premature seedling death. In the following two weeks, the Li-exposed plants showed a dose-dependent decrease in growth parameters and biomass yield. Lithium accumulated mainly in the leaves and affected the accumulation and translocation of various mineral elements in the plants, disrupting their content and stoichiometric ratios. In the leaves, all the applied Li concentrations caused a decline in photosynthetic pigment content. They also led to significant changes in antioxidant enzyme activities: superoxide dismutase (SOD), catalase, and class III peroxidases (POD) in the leaves, and SOD, ascorbate peroxidase, and POD activities in the roots, indicating the increased formation of reactive oxygen species. The overall results indicate that, despite the initial stimulatory influence, even low doses of Li exert inhibitory effects on plant growth and the examined physiological parameters in the subsequent period. Therefore, longer-term investigations are required, covering a broader range of growth, development, and functional parameters prior to plant maturation. This is particularly important given that cabbage is an economically important plant and one of the most commonly consumed vegetables in Serbia and across Europe.