Multi-trophic responses to Moso bamboo expansion: Soil properties drive shifts in microbial and nematode communities

Expansion of moso bamboo ( Phyllostachys edulis ) into Japanese cedar ( Cryptomeria japonica ) forests profoundly alters soil properties and belowground biota communities. However, the mechanistic links between bamboo-driven soil physicochemical changes and multi-trophic community shifts remain unclear. This study used a space-for-time substitution and high-throughput amplicon sequencing approach to examine soil physicochemical properties, diversity and community structure of fungi, bacteria, and nematodes of three forest types, moso bamboo, Japanese cedar, and their mixed forest, across two soil layers (0–10 and 10–20 cm) to assess these impacts. Moso bamboo expansion increased subsoil bulk density 12.7% and reduced moisture by 14.7% versus mixed stands; mixed stands raised pH ∼5.5% higher than in cedar stands. Relative to cedar, fungal richness then rose by 29% at 0–10 cm and by 45% at 10–20 cm, whereas within the 0–20 cm layer bacterial richness rose by 6.9% and nematode richness by 24–28%. Mixed and moso bamboo stands had higher ammonium and available potassium but lower nitrate, suggesting enhanced ammonification and transient suppression of nitrification. Bacterial diversity peaked in mixed forests but declined under pure bamboo, whereas fungal abundance and diversity rose steadily from cedar to moso bamboo. Microbes shifted from homogeneous, oligotrophic (Acidobacteriota/Ascomycota) cedar assemblages to heterogeneous, copiotrophic bamboo communities dominated by Proteobacteria, Actinobacteriota, Chloroflexi and Basidiomycota. Nematode communities shifted toward fungivorous and K -selected strategists (cp2), indicating a fungal-dominated energy channel. Our results reveal coupled, multi-trophic responses to moso bamboo expansion and highlight potential feedbacks among bamboo, soil biota, and nutrient cycling.