Beneficial and Adverse Effects of Bio‐Inoculation on Predicted Functional Microbial Communities in Salt‐Land Restoration

ABSTRACT Bioinoculants are increasingly used in land restoration programs to alleviate environmental stress during tree establishment and to enhance vegetation recovery in degraded ecosystems. However, their effects on native soil microbiota remain insufficiently understood, particularly in highly vulnerable environments, limiting their large‐scale application. In salt‐affected lands of Senegal, restoration strategies rely on Casuarinaceae species inoculated with a multi‐kingdom bioinoculant composed of salt‐tolerant arbuscular mycorrhizal fungi and nitrogen‐fixing bacteria. While this strategy successfully enhanced tree growth and understory vegetation, its consequences for soil microbial diversity and functions have never been assessed. The objective of this study was to assess whether bioinoculation alters soil microbiota and to determine the relative influence of bioinoculation compared with salinity and host plant identity. We hypothesized that bioinoculation reshapes both soil bacterial and fungal microbial communities, with implications notably on soil nutrient cycling, but that these effects are constrained by salinity and Casuarinaceae species. Our results show that bioinoculation reduced overall fungal diversity without affecting rare taxa, whereas bacterial diversity was primarily driven by salinity and host plant identity, with effects largely confined to dominant bacterial groups. Functional predictions revealed marked shifts, with bioinoculation associated with a decrease in potential bacterial pathogen guilds, while increasing salinity promoted potential fungal pathogen guilds. Bacterial‐mediated nitrogen cycling responded jointly to salinity and host plant identity, whereas nitrogen‐fixing bacterial taxa were specifically promoted by bioinoculation. Overall, our findings demonstrate that bioinoculation can significantly modify soil microbial diversity and predicted functions in salt‐affected soils, but that its effects may be overridden by strong environmental constraints and host plant effects. These results highlight ecological trade‐offs associated with bioinoculant use and emphasize the need to integrate soil microbial responses into sustainable salt‐affected land restoration strategies.