Lithium in the Environment and its Effects on Higher Plants

Abstract

Summary Lithium (Li) is present in low concentrations in all parts of the biosphere, including living organisms. It reaches the terrestrial environment primarily through natural processes to which parent substrate was subjected during pedogenesis, and due to anthropogenic activities. Individual soil types differ regarding Li content; for example saline and loamy soils have higher Li content. It is found in low concentrations primarily in ionic form in aquatic environments in surface and groundwater. It is mobile in the soil and thus soil contamination with Li can lead to its higher concentration in groundwater. In the environment, Li reaches the atmosphere from Li-emitting sources. It is widely used in many industries, lately in the Li-ion batteries in electronic goods, due to which it may be a potential risk for the environment. Terrestrial plants take up Li largely via roots from the soil, but also via shoots from the atmosphere. In the soil, Li is mostly bound by clay fraction and organic matter. During the uptake, transport and distribution in plants it behaves like an alkaline earth ion, not like an alkali ion. The fact that Li is immobile in the phloem supports this claim. Its ascendent transport mainly depends upon the transpiration intensity. More Li is taken up by plants from acid soils than from alkaline soils. Li is non-essential for plant growth and development. In low concentrations it can be stimulative and affect chemical composition and organic production of plants. Li plays an important role in the metabolism of halophyte species. It is increasingly regarded as an essential trace element for animals and humans, and used in human medication to treat dementia, suicidal ideation, aggression and violence. High levels of Li are toxic to all plants, but uptake and sensitivity to Li are species-dependent. Some representatives of the Ranunculaceae, Solanaceae and Asteraceae families are characterized by increased Li accumulation, while Poaceae, Liliaceae, Brassicaceae, Caprifoliaceae show low accumulation. High concentrations of Li have adverse effects on many physiological and biochemical processes in plants (DNA, RNA and protein pathways, water relations, content of photosynthetic pigments, photosynthesis, production of reactive oxygen species, lipid peroxidation of the cell membranes etc.), which is further manifested as stunted growth, developmental disorder, visual symptoms, interveinal necrosis and necrosis along the leaf margins. Hyperaccumulator plants extract significant amounts of Li and are therefore used in phytoremediation. Better understanding of the effects of beneficial and phytotoxic concentrations of Li on metabolism and plant growth and development remains vital for the improvement of the knowledge about biological activity of Li in higher plants.