Keystone fungal taxa play a more vital role in regulating rhizosphere soil ecosystem multifunctionality than keystone bacterial taxa in early succession

Soil ecosystem multifunctionality (EMF) is crucial in regulating nutrient cycling, enhancing biodiversity, and maintaining ecosystem stability. However, how keystone taxa affect soil EMF in early succession remains unclear. Here, we investigated changes in soil properties, microbial characteristics, and soil EMF in seedlings’ rhizosphere across different canopy densities, including forest gap (FG), forest edge (FE), medium canopy density (0.4-0.6, MCD), and high canopy density (0.7-0.9, HCD), and further clarified the primary factors regulating soil EMF. Our results revealed that canopy density significantly affected soil properties, microbial characteristics, and soil EMF (p < 0.05). Specifically, rhizosphere soil nutrient concentrations (i.e., soil available potassium (SAK), ammonium nitrogen (NH4+–N), soil organic carbon (SOC), and total nitrogen (TN)) and soil EMF in FE were significantly higher than those in other treatments. Soil microbial communities were limited by phosphorus in all canopy densities. Co-occurrence network analysis showed that average degrees and linkage densities of bacterial and fungal networks peaked in FG and HCD, respectively. Spearman's analysis demonstrated that keystone bacterial and fungal taxa diversities were significantly affected by soil nutrients and enzymatic activity characteristics. Random forest revealed that soil EMF was simultaneously influenced by soil properties, enzymatic activity, microbial biomass, and keystone taxa diversity. Both variance partitioning analysis and structural equation modeling illustrated that keystone fungal taxa played more crucial roles than keystone bacterial taxa in regulating soil EMF. Overall, the findings indicated that the forest edge was conducive to maintaining soil EMF and highlighted the importance of keystone fungal taxa in regulating soil EMF.