Seasonal Patterns of Soil Bacterial and Fungal Communities Under Practical Organic Fertilizer Regimes in a Tea Plantation

Organic fertilizer and season are established sources of variation in tea plantation soil microbiomes. A repeated-measure field experiment was conducted in Yunnan, China, comprising an unfertilized control (CK), sheep manure (SM), pig manure (PM), rapeseed cake manure (RM), and commercial organic fertilizer (OF). The same 15 mature tea trees were sampled in spring, summer, and autumn, yielding 45 composite soil samples. Soil properties, as well as 16S rRNA gene and ITS amplicon profiles, were evaluated using mixed-effect models, restricted-permutation PERMANOVA, and design-adjusted partial redundancy analysis (pRDA). Fertilization regime, season, and their interaction showed property-specific associations, most clearly for alkali-hydrolyzable nitrogen, available phosphorus, and available potassium. Bacterial alpha diversity was more responsive than fungal alpha diversity. Both factors were significantly associated with bacterial and fungal community structures. Season accounted for most bacterial variation (68.70%), whereas fungal variation was associated more evenly with season (27.33%) and fertilization regime (18.61%); no significant interaction was detected for either group. Nine fungal genera retained significant treatment-associated differences after FDR correction, whereas the bacterial genus-level patterns remained exploratory. After conditioning for fertilization regime and season, measured soil variables collectively explained 6.51% and 13.56% of bacterial and fungal variation, respectively, but no individual variable remained significant after FDR correction. Because fertilizer inputs were not nutrient-standardized, treatment contrasts represent integrated material-and-dose regimes rather than isolated fertilizer-type effects. These context-specific results illustrate the value of repeated seasonal sampling with design-adjusted analyses for evaluating practical fertilization regimes.