Shading and planting density drive changes in soil microbial communities and wrapper leaves productivity

Soil microorganisms regulate nutrient cycling and yield formation in cigar tobacco; however, how agronomic practices reshape microbial communities across soil compartments remain unclear. A field experiment was conducted in Hainan to analyze the effects of shading and planting density on soil physicochemical properties, microbial communities, and wrapper leaf yield. Rhizosphere soil was enriched in total nitrogen and alkaline-hydrolyzable nitrogen, whereas bulk soil contained higher total and available phosphorus ( P < 0.05). Delayed shading promoted Sphingobium and Arthrobacter in the rhizosphere, whereas high-density planting increased Chujaibacter and Penicillium in bulk soil ( P < 0.05). Bacterial α-diversity was higher in bulk soil but declined under high-density planting, whereas fungal α-diversity responded more strongly in the rhizosphere ( P < 0.05). Bacterial β-diversity indicated tighter rhizosphere community convergence and higher bulk soil heterogeneity. RDA and Mantel analyses associated the rhizosphere communities mainly with nitrogen and organic carbon and bulk soil communities with phosphorus and pH ( P < 0.05). Functional prediction indicated the predominance of metabolism-related pathways. Delayed shading increased the total and high-grade wrapper yields, whereas high-density planting reduced the yield performance ( P < 0.05). Random forest analysis and structural equation modeling identified the bacterial community structure, especially in bulk soil, as the principal mediator linking agronomic practices to yield. Overall, moderately delayed shading with medium-to-low planting density improved soil nutrient distribution and microbial community structure, thereby enhancing wrapper leaf yield and quality.