Reduced soil ecosystem multifunctionality is associated with altered complexity of the bacterial-fungal interkingdom network under salinization pressure

Salinization processes profoundly impact soil quality and health, altering physical structure, chemical composition, and biological activity, particularly concerning soil microbial populations. Microbial communities play a pivotal role in maintaining soil ecosystem multifunctionality (EMF). Understanding the response of microbial communities to salinity stress is crucial for sustainable soil management and enhancing ecosystem resilience in arid and semi-arid regions. This study assessed microbial diversity, composition, and the properties of bacterial- fungal interkingdom networks, and explored their relationship with EMF in saline soil ecosystems in Ningxia. The findings revealed that soil salinization was more pronounced in Hongsipu (HSP) and Xidatan (XDT) compared to Huinong (HN). Bacterial diversity indices, including shannon and chao1, were more sensitive to soil type and salinity level than their fungal counterparts. High salinity levels significantly reduced bacterial diversity indices, even across different saline soil types. The structure and composition of bacterial and fungal communities were influenced by the type and degree of soil salinization. Despite these variations, the dominant bacterial phylum Proteobacteria (11.75%-24.88%) and fungal Ascomycota (47.93%-80.11%) remained consistent across salinized soil types and salinity levels. Salinity stress, however, substantially reduced network complexity and stability while promoting cooperative interactions between bacterial and fungal species. Correlation analyses indicated significant positive relationships between EMF and microbial community diversity, as well as network complexity and stability. When integrating the relationships between soil salinity, microbial diversity, network characteristics, and EMF, the positive, strong, and significant effect of network complexity on EMF persisted. These findings underscore the critical role of bacterial-fungal interkingdom network complexity as a key determinant influencing EMF in salinized soils. This study highlights the necessity of addressing microbial network properties to mitigate the adverse effects of salinity on soil ecosystems and maintain multifunctionality under salinization stress.