Allelopathic Effect of <i>Osmanthus fragrans</i> Changes the Soil Microbial Community and Increases the Soil Nutrients and the Aroma Quality of Tea Leaves

Intercropping is a sustainable agricultural practice that promotes the growth of tea plants. However, research on the effects of intercropping with aromatic plants on the soil environment and tea aroma quality remains limited. In this study, we conducted both greenhouse and field experiments to investigate the allelopathic effect of <i>Osmanthus fragrans</i> on soil properties, the soil microbial community, and tea aroma quality. The treatment with <i>O. fragrans</i> leaf litter or intercropping significantly increased soil pH and ammonium nitrogen content and changed soil enzyme activities. Both treatments enhanced the bacterial richness in rhizosphere soil and altered microbial communities, particularly increasing the relative and absolute abundance of beneficial <i>Bacillus</i>. The allelopathic effect of <i>O. fragrans</i> improved tea aroma quality, with five key volatile compounds (linalool oxide II, linalool, nonanal, methyl salicylate, and geraniol) consistently identified in both greenhouse and field treatments. Network analysis demonstrated that our treatments enhanced the correlation between soil bacterial communities and five volatile compounds in tea leaves. These findings provide a theoretical foundation for improving soil health and tea aroma in tea plantations.