Rhizosphere microbiota mediated by sulfur fertilizer regulates flavor quality in peppers (Capsicum annuum L.)

Although sulfur (S) fertilizer is known to enhance flavor quality in S-rich pungent vegetables, its role in regulating non-S flavor compounds, such as capsaicinoids in peppers (Capsicum annuum L.), remains unclear. Here, field experiments were conducted using three treatments: S fertilizer (ammonium sulfate), nitrogen fertilizer (urea), and an unfertilized control (CK). Pepper yield, flavor compounds (capsaicinoids, soluble sugars, vitamin C, and volatiles), and rhizosphere microbiota were analyzed. The results showed that S fertilizer significantly increased the contents of soluble sugars, vitamin C, capsaicinoids, and 15 volatile compounds such as benzyl benzoate, (E,E)-2,4-nonadienal, and β-ionone, collectively achieving optimal pungent flavor. Moreover, S fertilizer reduced bacterial diversity and richness in the rhizosphere soil but exhibited minimal impact on fungal community structure. Notably, the bacterial genera unidentified_WD2101_oil_group and Rhizomicrobium were identified as potential key taxa enhancing capsaicinoid accumulation under S fertilizer. Additionally, Sphaerobacter (bacteria) and Pseudogymnoascus (fungi) emerged as critical microbial candidates driving the synthesis of volatile compounds in S-amended soils. This study provides new insights into the roles of rhizosphere microbiota under S fertilization, emphasizing their importance in improving pepper yield and quality.