The interaction between litter input and soil microbial community regulates the intraspecific allelopathic effects of Solanum rostratum Dunal

Introduction The "novel weapon hypothesis" posits that invasive plants suppress native species by releasing allelochemicals, which is a crucial factor for their successful invasion. While most studies focus on interspecific allelopathy, with insufficient attention paid to intraspecific allelopathy. Methods This study employed an in pot experiment with different litter concentrations (0, 5, 10, 20 g/kg) to cultivate Solanum rostratum Dunal seedlings in both sterilized and unsterilized soils. The plant growth parameters, soil physicochemical properties, soil metabolites, and soil microbial communities were measured, and their interrelationships were also analyzed. Results The results indicated that the litter from Solanum rostratum Dunal significantly inhibited the growth of its seedlings, and the inhibitory effect is even stronger in sterile soil. Additionally, the addition of litter decreased the soil pH value, while increasing the soil electrical conductivity, total carbon, total nitrogen and total phosphorus contents. Metabolomic analysis identified the phenolic compound 4-Ethyl-2-methylphenol and the ester compound Carvyl propionate as main secondary metabolites in soil, whose concentrations showed significant negative correlations with seedling growth. In unsterilized soil, the abundance of Sphingomonas and Dongia —bacteria with degradation potential—increased, exhibiting negative correlations with allelopathic metabolite levels and positive correlations with seedling growth indicators. Discussion In summary, the self toxic effect of Solanum rostratum Dunal litter on seedling growth increased with the increasing of litter content, and soil microorganisms mitigate the allelopathic effects by degrading or transforming allelopathic compounds in litter, thereby playing a crucial role in regulating its invasion process.