Seaweed liquid extracts induce hormetic growth responses in mung bean plants

Hormesis is a dose–response phenomenon that is characterized by stimulation at low doses and inhibition at high doses. Extensive evidence has accumulated showing the occurrence of hormesis in numerous plant species independent of physicochemical agents, and this phenomenon has become a target for achieving greater crop productivity. Biostimulants (i.e., elicitors) are agents that activate adaptive responses, moderately stimulate biological performance and aid plants in tolerating stress when applied at low doses that fall within the stimulatory zone of a dose–response curve. Biostimulants based on seaweed liquid extracts (SLEs) are widely known to exert great benefits in plants at very low doses. However, the consequences to plants when SLEs are applied at high doses remain underexplored. A dose–response study was performed on mung bean (Vigna radiata) seedlings by applying a wide range of SLE doses to evaluate growth stimulation patterns. While the application of SLEs at high concentrations mostly caused a decrease in various morphological parameters, the application of SLEs at low concentrations stimulated some of these. Nevertheless, common features of SLE stimulation were present. Mung bean shoot length, root length, and dry weight responded to the SLE concentrations in a hormetic manner. A biphasic dose–response confirmed the relationships between SLE dose and mung bean plant growth parameters, which were due to the properties of the constituents of the SLE of each seaweed species. The SLE growth stimulation pattern found in this study will contribute to the establishment of safe application doses. This paper provides a strong foundation for enhancing the research protocols of studies on the effects of SLEs on plant growth and supports incorporating hormesis into risk assessment practices in agriculture.