Soil Invertebrate Body Size Groups and Effect Magnitude Jointly Influence Global Soil CO₂ Emissions

Soil invertebrates represent vital components of belowground biodiversity and play pivotal roles in regulating key carbon (C) cycling processes, particularly soil respiration. Despite the recognised effects of invertebrates on soil respiration, previous studies suffer from a major blind spot: a lack of global-scale interpretations of inferred associations describing how these organisms mediate C release. In this study, we integrated 556 datasets spanning 90 publications to systematically assess the global patterns and inferred associations by which soil invertebrates influence soil respiration. The results revealed that soil invertebrates, on average, enhanced soil respiration by 52%. Across climatic zones, the magnitude of this positive effect tended to decline from tropical to temperate regions. When classified by body size, among the large-bodied soil invertebrates, ants and termites increased soil respiration by 60% and 62%, respectively, whereas earthworms stimulated it by 47%. In contrast, small-to-medium-bodied soil invertebrates exerted no significant effect. Across ecosystem types, soil invertebrates stimulated soil respiration more strongly in forest ecosystems, with an increase of 55%, compared to a 44% increase in grassland ecosystems. The pathways through which soil invertebrates influence respiration varied markedly among body-size groups and ecosystem types. Overall, soil invertebrates primarily influenced soil microbial biomass C, fungal biomass and bacterial biomass, as well as soil organic N, soil organic C and soil pH, which in turn were closely associated with soil respiration. These findings underscore the key role of soil invertebrates in influencing soil CO₂ emissions and provide insights essential for improving Earth system models under ongoing climate change.