The downhill positions exhibit higher microbial network complexity and ecosystem multifunctionality compared to the upper slopes.

Soil microbial communities play a crucial role in regulating multiple ecosystem functions. However, the specific influence of functional microbiomes, such as protists, bacteria, and fungi, and their interactions in response to ecosystem multifunctionality along slope positions remains largely unknown. We investigated the relationship between ecosystem multifunctionality and microbial index in the downhill, middle, and upper slopes of karst ecosystems. Compared to the upper slope, ecosystem functions related to microbial biomass, nutrient storage, plant-soil mutualism, plant productivity, and multifunctionality were higher in the downhill position. Bacterial and fungal abundance showed higher levels in the downhill position and middle slope than in upper slope. However, the composition and diversity of protists, bacteria, and fungi did not show significant differences across the downhill, middle, and upper slopes. Co-occurrence network analysis revealed that the downhill position had a higher microbial network complexity among bacterial taxa (e.g., Proteobacteria and Actinobacteria), fungal taxa (e.g., Ascomycota and certain unclassified taxa), and protistan taxa (e.g., Conosa and certain unclassified taxa) compared to the upper slope. Furthermore, bacterial diversity and network properties (e.g., the number of nodes, edges, and modules) were positively associated with ecosystem multifunctionality. These findings suggest that microbial network complexity is a key driver of ecosystem multifunctionality, indicating the crucial role of interactions among protistan, bacterial, and fungal taxa in soil functioning. Consequently, this study highlights the importance of microbial networks in maintaining the sustainability of ecosystems, emphasizing their stronger implications compared to biodiversity alone. [Display omitted] • Higher bacterial and fungal abundance in the downhill position than in the upper slope. • Microbial diversity and community composition were similar across the slope positions. • Increased ecosystem multifunctionality and network complexity in the downhill position. • Microbial network complexity is the most biotic predictor on multifunctionality. • Highlight the crucial role of microbial interaction in ecosystem multifunctionality. [ABSTRACT FROM AUTHOR]