Coumaric acid stressed soil_ITS Raw sequence reads
Phenolic acids significantly contribute to tobacco replant disease, yet the extent and mechanisms of their impact remain poorly understood. This study investigated the allelopathic effects of six phenolic acids identified for their cumulative effects, with findings indicating a concentration-dependent inhibition of tobacco plant growth. Coumaric acid, in particular, exerted the most potent direct allelopathic effects. Further analysis involving the exogenous addition of coumaric acid revealed that coumaric acid stress significantly impeded normal tobacco plant growth and reduced soil pH, organic matter content, and enzyme activity, with nearly all these effects showing dose-dependent responses. Furthermore, coumaric acid stress transitioned the soil microbial community from a bacterial to a fungal predominance and gradually enriched microbial groups that influence soil nutrient dynamics and promote pathogen transmission and proliferation. Structural equation modeling indicated that coumaric acid suppressed tobacco growth indirectly by affecting soil pH, bacterial and fungal diversity, and soil enzyme activity, and directly by impacting tobacco leaf malondialdehyde activity and resistance hormone (jasmonic acid and the jasmonate-isoleucine complex) levels. Overall, the accumulation of coumaric acid may play a crucial role in tobacco replant disease by influencing the physiological processes in tobacco plants directly and the broader soil microecological balance indirectly.