Rare rather than abundant taxa of soil bacteria and fungi regulate soil multifunctionality in Eucalyptus plantations

Soil multifunctionality not only contributes to the production of ecosystem services (e.g., nutrient cycling, boosts in plant production, and provision of biological processes), but also supports the survival of species (protecting biodiversity) in an ecosystem. Multi-generational planting (sprouting from logging stumps) of Eucalyptus is widely adopted for timber production in southern China, which distinctly induces the decline of soil properties and destroys soil microbial communities. However, research on various Eucalyptus management practices has predominantly concentrated on soil nutrients and microbial populations. The effects of these practices on soil multifunctionality remain unexplored. Furthermore, the underlying mechanisms influencing the abundant and rare microorganisms have not been fully understood. Here, an 18-year Eucalyptus plantation experiment, including single-generation continuous planting (Y18), multiple-generation felling of the same years (D4), and evergreen broadleaf forest control (CK), was designed. Twenty-three parameters associated with soil nutrient cycling were obtained to quantify soil multifunctionality, and partial least squares path modeling (PLS-PM) was used to reveal the main driving force regulating soil multifunctionality. Our results demonstrated that multi-generational Eucalyptus planting significantly reduced soil multifunctionality, microbial diversity, and network stability. Comparatively, single-generational planting showed slight effects on soil multifunctionality and microbial communities. Stochastic processes dominated the assembly of abundant taxa in Eucalyptus plantations, whereas deterministic processes dominated rare taxa. PLS-PM results revealed that soil organic carbon (SOC), dissolved organic carbon (DOC), total nitrogen (TN), and total phosphorus (TP) directly regulated soil multifunctionality or indirectly through modifying the diversity and networks of rare taxa. The total effect analysis showed that the diversity and network of rare taxa had a greater impact on soil multifunctionality than abundant taxa. SOC and DOC played a crucial role in driving changes in soil multifunctionality. Our findings highlight the need to decrease rotation intensity and conserve rare taxa to mitigate soil quality degradation in artificial Eucalyptus plantations.