The effects of long-term continuous cropping of peppers on soil properties, microbial communities and root exudates

Replant disease has emerged as a significant issue affecting the stable progress of modern agriculture. Therefore, it is crucial to identify the causative factors of replanting disease to propose effective solutions. Soil from pepper plants after 1 year of cultivation, 3 years of continuous cropping, and 6 years of continuous cropping were used as the subject of this research to analyze the diversity and composition of the soil microbial community through high-throughput sequencing. Additionally, soil nutrients and root exudates were measured to explore the effects of long-term continuous cropping of peppers on soil. The results showed that continuous cropping of peppers led to a decrease in soil pH, available phosphorus, hydrolyzable nitrogen, organic matter content, and enzymatic activity while available potassium was accumulated. Twenty-nine compounds and five phenolic acids were detected in the soil used for continuous pepper cropping, of which octadecanoic acid, palmitic acid, 2,4-di-tert-butylphenol, hexadecanal, phthalic acid, 4-coumaric acid, and malic acid were found to be important autotoxic substances. Furthermore, Short-term continuous cropping can enrich the soil with beneficial bacteria and promote the degradation of some phenolic acids, but beyond a certain duration, degradation is inhibited, and phenolic acids begin to accumulate. The composition and structure of the soil microbial community were also changed, with an increase in soil fungi diversity and a decrease in bacterial diversity, accompanied by a gradual shift from "fungal" to "bacterial" soil. Redundancy analysis showed that salicylic acid and hydrolyzable nitrogen were the main factors influencing changes in the soil microbial community. The results provide a reference for addressing the causative factors of pepper replant disease and effectively controlling its occurrence.