No consistent latitudinal biodiversity gradients in soil biodiversity (Supplementary tables S1-S20)

The latitudinal diversity gradient (LDG), a foundational pattern describing increasing biodiversity toward the Equator, has been extensively documented for aboveground organisms. However, whether this pattern holds for belowground biodiversity—the largest component of Earth’s biodiversity—remains unclear. Here, we integrated two independent global databases encompassing over 5,000 soil samples (amplicon and metagenomics) across multiple trophic levels, including archaea, bacteria, fungi, protists, and invertebrates. Our results demonstrate that multitrophic soil biodiversity deviates substantially from the classical LDG, with most taxa do not follow the expected decline in diversity with increasing latitude. Moreover, beta diversity and community turnover were highest at mid- to high latitudes. We further found that local-scale edaphic properties (e.g., soil carbon, nitrogen, and pH) and global-scale climatic variables (e.g., rainfall and temperature), largely overrides latitude in explaining soil biodiversity variations. Multi-group structural equation modeling indicated that local diversity was primarily governed by regional diversity and soil nitrogen availability, suggesting that nutrient supply mediates spatial variation in community assembly across regions. Collectively, our findings challenge the universality of the classical LDG and advance our understanding of the mechanisms shaping global soil biodiversity patterns.