Aim Soil respiration (RS) is one of the largest fluxes in the global carbon cycle. It is composed of respiration by roots and heterotrophic organisms, with each component having distinctive drivers and sensitivities and, consequently, varying feedback potential to climate change. Global drivers of the total flux of RS are widely studied and generally accepted, but our understanding of the factors governing its component fluxes lags far behind. Location Global. Time period 1962–2015. Major taxa studied Plant roots and soil microbes. Methods Combining a newly updated global database of RS partitioning measurements with biotic and abiotic variables, we examined the world‐wide distribution of the proportion of the annual root respiration (Rroot) contribution to RS (Rroot:RS). We investigated how Rroot:RS varies by ecosystem type, measurement method and climate. We used a random forest model to predict the relationship between field measurements of Rroot:RS (n = 880) and 14 biotic and abiotic factors, including climate, nitrogen deposition, soil, mycorrhiza, biomass and satellite‐derived greenness. Finally, we present a global map of predicted Rroot:RS at 0.5° resolution. Results Consistent with previous studies, we found no clear trends of mean Rroot:RS across ecosystem types and measurement methods. The area‐weighted overall mean of predicted Rroot:RS was .42 (SD ± .18; i.e., 42% of total global RS was generated by plant roots). Predicted Rroot:RS and related environmental factors did exhibit clear spatial patterns between climatic regions, with higher Rroot:RS in dry and cold regions and lower Rroot:RS in temperate and tropical regions. Main conclusions Given that Rroot:RS is linked to plant carbon use efficiency (CUE, the ratio of net primary production to gross primary production), but generated from measurements completely independent of plant CUE, it might provide crucial insights into ecosystem‐ to global‐scale carbon cycling. This study thus provides a framework to explore global carbon allocation under global climate change.