International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.5, 240-248 http://ecoevopublisher.com/index.php/ijmec 24 1 Against the backdrop of increasingly intensified global environmental changes, the allelopathic effect of black walnut may demonstrate new ecological functions in resisting invasive plants and regulating community structure. This study aims to systematically sort out the sources and types of sensitivities in black walnut, the mechanism of action and ecological functions of juglanone, and further explore its adaptive significance in the application of forest farmers and in the context of global change, providing theoretical support for future research and management practices. 2 The Sources and Types of the Sensitizing Substances in Black Walnut 2.1 Chemosensory substances released from various parts of the tree The sensitizing effect of black walnut stems from a series of secondary metabolites produced and released within its body. Studies have shown that various tissues of black walnut trees, such as root systems, bark, leaves, and fruit peels, all contain sensitizing active substances, which can be released into the environment through root secretion, leaching of leaf litter, and other pathways (Liu et al., 2022; Xu et al., 2023). Two representative secondary metabolites rich in walnut peels: Ellagic acid and Juglone (Figure 1). The green pericarp (unripe exocarp) of the walnut tree is regarded as the part with the highest walnut ketone content, with 20 to 40 milligrams of walnut ketone per 100 grams of green pericarp, while the content in leaves is approximately 5 to 23 milligrams per 100 grams. During the process of leaf fall and fruit peel decomposition in autumn, a large amount of substances such as juglanone and phenolic acids are released into the soil (Medic et al., 2021a; Liu et al., 2022). Figure 1 Chemical composition of key secondary metabolites in the husk of black walnut (Adopted from Jahanban-Esfahlan et al., 2019) Juglandone in black walnut trees is initially stored in living tissues in the form of non-toxic glycosides. Once it enters the soil, it will be hydrolyzed and oxidized to toxic free juglandone (Xu et al., 2023). In addition to juglanone, the leaves and green peels of black walnut are also rich in other phenolic compounds, such as tannins, caffeic acid, gallic acid, etc. They may jointly exert a complex chemosensory effect with juglanone (Zubay et al., 2021; Athaillah et al., 2024). Modern analysis has confirmed that the residues of black walnut harvesting (branches, leaves, shells, etc.) contain various phenolic substances, and these by-products can be used as raw materials for extracting natural products (Medic et al., 2021a). 2.2 Key sensitizing substances: Juglone Juglandone (5-hydroxy-1, 4-naphthoquinone) is the main allelopathic substance released by black walnut and other Juglandaceae plants, and it is also the earliest identified allelopathic component of walnut (Islam and Widhalm, 2020; Liu et al., 2022). Walnut ketone belongs to the naphthoquinone class of compounds. The pure product is yellow crystals and has high chemical stability in soil, which can exist for several months or even a year.
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