Canopy closure and litter management in coniferous plantation modulate the bacterial community to increase soil nitrogen mineralization and understory medicinal tuber yield

Forest canopy closure and litter management are critical factors regulating ecosystem processes, yet their interactive effects on soil nitrogen (N) cycling, microbial communities, and the production of understory tuberous medicinal plants remain elusive. This study investigated the impacts of varying canopy closure levels (low, medium, and high) and litter treatments (cover and removal) on these processes. Decreasing canopy closure significantly decreased soil moisture but increased soil temperature and net nitrification with canopy closure being a primary driver of N mineralization. Compared with litter cover, litter removal enhanced N mineralization and net ammonification only under high canopy closure. Canopy closure significantly altered microbial community composition by modifying soil temperature and moisture, whereas litter treatment had minor effects. Under low canopy closure, aerial stem length, rhizome length and tuber yield of understory medicinal herb Corydalis yanhusuo were 20 % – 42 %, 20 % – 61 %, and 156 % – 729 % higher than moderate and high canopy closures, respectively. Litter removal increased tuber yield only under low canopy closure. Structural equation modeling revealed that bacterial communities, particularly functionally important taxa, played a central role in N mineralization and plant productivity. These findings suggest that canopy closure, rather than litter treatment, predominantly regulates soil N mineralization and microbial functionality within forest ecosystems, highlighting the pivotal role of canopy closure in promoting plant productivity. This study underscores the importance of canopy management in enhancing N mineralization, regulating microbial community composition, and improving the productivity of understory medicinal herbs, thereby offering essential scientific support for sustainable forest management and the cultivation of medicinal crops. Conceptual diagram summarizing the integrated pathways by which canopy closure regulates microclimate, microbial community structure, and nitrogen cycling to influence understory plant productivity. • Canopy closure rather than litter management altered soil microbial composition. • Reduced canopy closure increased soil net nitrification rather than ammonification. • Canopy closure regulated soil N mineralization via microclimate and microbiomes. • Canopy closure enhanced photosynthesis and N supply favoring higher tuber yield.