Gradient Potassium Application Differentially Regulates Rhizosphere Bacterial and Fungal Communities in Cherry Tomato (Solanum lycopersicum var. cerasiforme)

Potassium (K) is an essential macronutrient for plants and plays a critical role in soil microbial processes. However, its systemic effects on rhizosphere microorganisms in high-value crops like cherry tomato remain poorly understood. This study established a potassium gradient (K0 represents the no-potassium application, K1 represents low-potassium application, K2 represents a moderate-potassium application, K3 represents the conventional-potassium application, and K4 represents excessive-potassium application) to investigate responses in growth and rhizosphere bacterial and fungal communities of cherry tomato. Moderate potassium (K2) significantly enhanced dry matter accumulation in cherry tomato. Bacterial and fungal communities displayed distinct patterns: bacterial structure shifted continuously along the gradient, with specific enrichment of functional genera (nitrogen-fixing Ensifer, biocontrol-related Lysobacter), increased unique OTUs, and gradual co-occurrence network optimization at K2. In contrast, fungal community composition and network structure showed threshold responses to potassium. Low K (K1) suppressed dominant Ascomycota and increased unclassified fungi, while high potassium (K4) enriched parasitic/pathogenic fungi (Alternaria, Curvularia), increased network modularity, and reduced stability. This microbial ecological perspective highlights that optimized potassium application regulates functional microorganisms and differentially shapes rhizosphere communities, providing a theoretical basis for precision potassium management in cherry tomato.