Abstract
Soil surface CO 2 flux ( R S ) is overwhelmingly the product of respiration by roots (autotrophic respiration, R A ) and soil organisms (heterotrophic respiration, R H ). Many studies have attempted to partition R S into these two components, with highly variable results. This study analyzes published data encompassing 54 forest sites and shows that R A and R H are each strongly ( R 2 >0.8) correlated to annual R S across a wide range of forest ecosystems. Monte Carlo simulation showed that these correlations were significantly stronger than any correlation introduced as an artefact of measurement method. Biome type, measurement method, mean annual temperature, soil drainage, and leaf habit were not significant. For sites with available data, there was a significant ( R 2 =0.56) correlation between total detritus input and R H , while R A was unrelated to net primary production. We discuss why R A and R H might be related to each other on large scales, as both ultimately depend on forest carbon balance and photosynthate supply. Limited data suggest that these or similar relationships have broad applicability in other ecosystem types. Site‐specific measurements are always more desirable than the application of inferred broad relationships, but belowground measurements are difficult and expensive, while measuring R S is straightforward and commonly done. Thus the relationships presented here provide a useful method that can help constrain estimates of terrestrial carbon budgets.