Linking Forest Litter Bacterial and Fungal Diversity to Litter–Soil Interface Characteristics

The mechanism by which litter–soil interface properties interact to shape the composition and diversity of litter decomposition-driving microorganisms remains unclear. Here, litter and surface soil samples were collected from three typical forest types on the Loess Plateau: Pinus tabulaeformis forest (PF), Quercus acutissima forest (QF), and their mixed forest (MF). Litter and soil chemical properties, along with litter microbial community structure, were analyzed to clarify microbial diversity differences across stands. Across the three forests, litter microbes showed no significant differences in multiple diversity indices, but dominant genera differed significantly. At all taxonomic levels, litter bacterial and fungal diversity followed the order MF < PF < QF. QF had the highest litter total nitrogen (LTN) and phosphorus (LTP) and significantly higher soil ammonia nitrogen (NH4+-N) than PF and MF. Correlation analysis indicated that LTN, LTP, soil organic carbon (SOC), and soil NH4+-N primarily influenced bacterial and fungal community composition and diversity. Redundancy analysis revealed litter organic carbon (LOC) as the dominant environmental driver shaping both communities, with soil NH4+-N exerting a stronger effect on bacteria and nitrate nitrogen (NO3−-N) on fungi. These findings deepen understanding of soil–litter–microbe interactions in forest ecosystems, laying a scientific foundation for forest management and protection.