Divergent responses of soil bacterial and fungal communities to different plantation restoration strategies in a subtropical forest of southern China

Understanding the response of soil microbial communities to different plantation reforestation strategies is crucial for tree species selection and successful forest restoration. In this study, we compared soil bacterial and fungal communities in topsoil (0–10 cm) and subsoil (10–30 cm) layers among three plantation restoration strategies, including Cunninghamia lanceolata plantation (CL), Liquidambar formosana plantation (LF), and the mixture plantation of L. formosana and Schima superba ( L. formosana-S. superba mixture forest, MIX), through high-throughput sequencing in a subtropical forest. Compared with the LF and MIX strategies, the CL restoration strategy showed the greatest recovery of bacterial richness, reaching 94.88% and 93.62% of the NF level based on the Chao1 index in the topsoil and subsoil, respectively ( p < 0.05). Notably, the projected subnetwork analysis showed that bacterial OTUs associated with the CL strategy and NF occupied smaller and less connected portions of the global co-occurrence network than those associated with AF, LF, and MIX. The null models revealed a shift in the assembly processes of the soil bacterial microbial community under the CL restoration strategy, transitioning from deterministic to stochastic and then returning to deterministic processes. In terms of fungi, the fungal α-diversity did not differ significantly among the three strategies. While fungal OTUs associated with the three restoration strategies occupied relatively larger and more connected portions of the global co-occurrence network. Fungal communities maintained stochastic assembly patterns across all restoration strategies. Specifically, soil organic carbon (SOC), pH, and clay content were identified as the key drivers of variability in bacterial α-diversity, β-diversity, and network parameters, whereas soil fungal communities showed minimal sensitivity to these soil factors. These results suggested that the historical land use and the original dominant tree species could be preferentially considered during the vegetation restoration in subtropical forests.