No consistent latitudinal biodiversity gradients in soil biodiversity

The latitudinal diversit gradient (LDG), a foundational pattern in ecology describing increasing biodiversity toward the Equator, has been extensively documented in aboveground systems. However, whether this pattern holds for belowground biodiversity—the largest component of Earth’s biodiversity—remains uncertain. To address this gap, we integrated two independent global databases comprising over 5,000 soil samples (amplicon and metagenomics) across multitrophic soil biodiversity, including archaea, bacteria, fungi, protists, and invertebrates. Our analyses revealed that soil biodiversity across multiple trophic levels largely deviate from the classical LDG, as most taxa do not follow the expected decline in diversity with increasing latitude. Moreover, beta diversity and community turnover peaked 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 variation. Multi-group structural equation modeling further indicated that local diversity was primarily driven by regional diversity and soil nitrogen, suggesting that nutrient availability mediates spatial variation in community assembly across regions. Together, these findings challenge the universality of the classical LDG and advance our understanding of the mechanisms shaping global soil biodiversity patterns.