Soil respiration ( R _s ) is the largest carbon (C) flux from terrestrial ecosystems to the atmosphere and is of great significance to the global C budget. An increasing number of studies have assessed R _s through in situ observations and model estimates over the last decades, but the sources and pathways of soil carbon dioxide (CO _2 ) are not fully understood, and great uncertainty remains in R _s partitioning of soil CO _2 sources. Here, we compiled 236 paired observations that measured soil CO _2 fluxes after concurrently removal of living roots (and rhizosphere), litter, and both roots and litter in plant input manipulation experiments conducted at 14 forest sites to partition root + rhizosphere ( R _r ), litter ( R _l ) and soil organic matter-derived microbial respiration ( R _m ) in total soil CO _2 flux. We found that R _r , R _l and R _m accounted for 20.1%, 21.8% and 62.7% of the total R _s , respectively. Mean annual precipitation (MAP) was the most important factor driving R _r / R _s , R _l / R _s and R _m / R _s , and MAP was positively correlated with R _r / R _s and R _l / R _s but negatively correlated with R _m / R _s , suggesting a significant climatic control over the proportions of R _s components. Across all sites, the proportions of R _r / R _s and R _l / R _s increased but R _m / R _s decreased with the increase in soil CO _2 flux, suggesting that the proportions of root- and litter-derived soil CO _2 are generally higher in the tropics than in cold temperate and boreal forests. More accurate partitioning of R _r , R _l and R _m to elucidate different sources and pathways of soil CO _2 flux will provide important insights for the global R _s assessment and terrestrial C budget.