Philip Martin, Leonora Fisher, Leticia Pérez-Izquierdo, Charlotte Biryol, Bertrand Guenet, Sebastiaan Luyssaert, Stefano Manzoni, Claire Menival, Mathieu Santonja, Rebecca Spake, Jan C Axmacher, Jorge Curiel Yuste

Anthropogenic climate change is altering precipitation regimes at a global scale. While precipitation changes have been linked to changes in the abundance and diversity of soil and litter invertebrate fauna in forests, general trends have remained elusive due to mixed results from primary studies. We used a meta-analysis based on 352 comparisons from 30 primary studies to address associated knowledge gaps, (i) quantifying impacts of precipitation change on forest soil and litter fauna abundance and diversity, (ii) exploring reasons for variation in impacts, and (iii) examining biases affecting the realism and accuracy of experimental studies. Precipitation reductions led to large decreases in soil and litter fauna abundance, with the opposite trend observed for precipitation increases, while diversity impacts were smaller. A statistical model containing an interaction between body size and the magnitude of precipitation change showed that mesofauna (e.g. mites, collembola) responded most to changes in precipitation. Changes in taxonomic richness were related solely to the magnitude of precipitation change. Our results suggest that body size is related to the ability of a taxon to survive under drought conditions, or to benefit from high precipitation. We also found that most experiments manipulated precipitation in a way that aligns better with predicted extreme climatic events than with predicted average annual changes in precipitation and that the experimental plots used in experiments were likely too small to accurately capture changes for mobile taxa. The relationship between body size and response to precipitation found here has far-reaching implications for our ability to predict future responses of soil biodiversity to and will help to produce more realistic mechanistic soil models which aim to simulate the responses of soils to global change.