Abstract
Cyanobacteria rapidly form harmful algal blooms (HABs) that cause serious nutritional imbalances in crop production via hydroponics. Allelopathic extracts from plants can be applied as a solution for ecologically sustainable control of algal blooms. In this study, the effects of 11 aqueous extracts of 10 allelopathic plants in controlling Microcystis aeruginosa were evaluated. Among the extracts, walnut husk and rose leaf extracts exhibited high inhibitory levels for efficient control of algae. High inhibitory levels were achieved owing to large amounts of water-soluble tannins, especially tannic acid. The effective extracts were applied to a hydroponic system cultivated on leafy perilla vegetables. Although the severe doses (IC90) did not guarantee complete algal control due to partial algal regrowth, walnut husk and rose leaf extracts only exerted strong persistent effects on algae control. Persistent algae inhibition contributed to the increase in perilla growth and leaf quality. Rose leaf was potentially a more useful resource for controlling algae in a hydroponic system because the application of rose leaf extract efficiently controlled the algae and was less toxic to perilla growth. In contrast, the treatment of walnut husk extract also controlled algae but inhibited perilla growth with pale green leaves.
Highlights
Hydroponics is an efficient culture system for producing crops in facilitated agriculture
Each aqueous extract was dissolved in an algal culture medium at concentrations ranging from 0.05 to 5 g L−1 to determine efficient concentrations to inhibit algal growth by 50% (IC50) and 90% (IC90) of non-treatment
Findings from this research can be used to distinguish between ambiguous allelopathic effects on either the inhibition or mortality of algae by measuring
Summary
Hydroponics is an efficient culture system for producing crops in facilitated agriculture. Hydroponics can benefit from the automatic control of irrigation and fertilization, ensuring a clean culture-environment and saving space due to multi-layer vertical production [2]. Despite these advantages, the occurrence of cyanobacteria is a main cause of giving up the hydroponics. Cyanobacteria naturally occur and thrive in hydroponic solutions as well as in eutrophic ponds, lakes, and rivers. They damage the ideal hydroponic solution by forming harmful algal blooms (HABs) quickly [3]. Cyanotoxins, which are generated by secondary metabolic processes in some species of cyanobacteria, are potentially hazardous to human health [7]
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