Contrasting the Relative Importance of Microbial Generalists and Specialists in Maintaining Assembly Processes and Community Stability

Microbial generalists and specialists play pivotal roles in community dynamics, yet their contributions to ecosystem stability under prolonged agricultural disturbance remain unclear. Here, to explore the different contributions of generalists and specialists to community stability, we collected 60 rhizosphere soil samples over three consecutive years (2021-2023) from long-term fertilised wheat fields on the Chinese Loess Plateau. We found that bacterial communities were dominated by generalists with higher microbial diversity, whereas fungal communities exhibited a contrasting pattern with a higher proportion of specialists. Bacterial generalists and specialists were predominantly shaped by homogeneous selection and dispersal limitation, respectively, while both fungal generalists and specialists were mainly governed by heterogeneous selection. We further found that soil NH₄ ⁺ and available phosphorus (AP) mediated the balance between stochastic and deterministic assembly of generalists and specialists. Combined with network and community stability analysis, we found that generalists enhanced community stability through greater network robustness and species cohesion, whereas specialists substantially contributed by reinforcing network modularity and enhancing ecological adaptation to environmental changes. Our findings indicate the distinct importance of the generalists and specialists in regulating community stability, providing valuable guidance for understanding relationships between community assembly and ecosystem stability under anthropogenic disturbances.