International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.5, 240-248 http://ecoevopublisher.com/index.php/ijmec 24 3 3.3 Sensitivity differences of receptor plants The sensitivity of different plants to walnut ketone varies significantly. Some species are highly susceptible, while others show certain tolerance (Nicolescu et al., 2020; Park et al., 2020). Generally speaking, dicotyledonous herbs and certain horticultural crops (such as tomatoes, potatoes, leguminous vegetables) are particularly sensitive to juglandone and often grow poorly or even fail to survive under black walnut trees, which has been widely reported in horticultural practice (Nicolescu et al., 2020). In contrast, some gramineous crops and shade-tolerant plants have a relatively mild response to juglanone. For instance, research has found that juglanone only slightly inhibits the sprout growth of cereal crops such as corn and wheat. In the intercropping system of black walnut and crops, crops such as wheat, corn, and oats only showed slight growth reduction and could coexist with walnut trees through reasonable planting density and management (Davies et al., 2011; Bishop et al., 2024). Bishop et al. (2024) of the walnut alley cropping (intercropping of forest farmers) study indicated that wheat and barley showed only slight growth retardation under walnut ketone stress, while the germination of many dicotyledonous weeds was significantly inhibited. This selectivity may stem from physiological and biochemical differences among species: tolerant species may have higher detoxification enzyme activity or thicker rhizosphere microbial membranes, which can degrade juglanone more quickly. However, the cell membrane permeability and antioxidant defense of sensitive species are relatively weak, and they are more vulnerable to damage by walnut ketone (Kanatas, 2020; Park et al., 2020). Even in lower plants such as algae, similar phenomena have been observed: walnut ketone has a strong inhibitory effect on the growth of harmful cyanobacteria, but has a relatively small effect on some diatoms (Park et al., 2020). It can be seen that the chemosensory effect of walnut ketone varies depending on the type of recipient plant. 4 The Ecological Function of the Black Walnut Transformation Strategy 4.1 The sensory advantage in resource competition Black walnut has gained a unique advantage in forest succession and resource competition through allelopathic effects. Substances such as walnut ketone released by its root system and fallen leaves can inhibit the growth of neighboring plants, thereby freeing up space for itself and obtaining more resources (Kanatas, 2020; Nicolescu et al., 2020). Research indicates that tree species with strong chemical sensitivity often reduce the plant coverage under the forest, weaken potential competitors, and thus consolidate their dominant position. This chemosensory competitive advantage compensates to some extent for the weakness of black walnut's intolerance to light and nutrients (Bertin et al., 2003). In fact, black walnut is a light-loving tree species with relatively weak competitiveness at the young tree stage. However, with chemosensory substances, it can "chemically clear the field", reduce the interference of shrubs and grass under the forest, and create favorable conditions for the growth of itself and its offspring (Nicolescu et al., 2020). Meanwhile, the sensiogenic substances of black walnut can also have an impact on the soil microenvironment. For example, they can inhibit the activity of certain microorganisms that antagonize walnut, indirectly enhancing their own utilization efficiency of soil resources (Kanatas, 2020; Islam and Widhalm, 2020). Underground interactions and their effects on soil microbial communities, nutrient cycling, root growth patterns, etc. can also be achieved through Allelochemicals (Figure 2) (Xu et al., 2023). 4.2 Impact on species diversity and community structure The allelopathic inhibitory effect of black walnut has a profound impact on the species diversity and structure of the community. Because walnut ketone can selectively inhibit the renewal of sensitive species, the composition of undergrowth plants often changes in the distribution area of black walnut, manifested as dominance of tolerant species and lack of sensitive species (Nicolescu et al., 2020; Zubay et al., 2021). In the long term, this selective pressure may reduce the species diversity of the community. On the other hand, from the perspective of community competition, the sensitization effect of black walnut may prevent certain highly competitive but sensitive species from invading, thereby maintaining its dominant position in the community. For instance, the survival rate of Ailanthus altissima seedlings, which are highly invasive, was significantly reduced in soil where walnut ketone was present (Ferus et al., 2020), which to some extent curbed the encroachment of ailanthus altissima on local vegetation. Therefore, the allelopathic effect of black walnut may both reduce local species diversity and protect the composition of the original community by inhibiting invasive species (Sujeeun et al., 2023).
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