Partitioning of root, litter and microbial respiration by plant input manipulation in forests

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.