LAUSR

Abstract Forest carbon exchange and use efficiency (the capacity of transferring gross primary production to net ecosystem production) play an important role in regulating the atmospheric carbon balance and thus affecting the climate. Here, we conducted a synthesis of eddy covariance fluxes measurement across China's typical forests to examine the magnitude, pattern and controls of forest carbon fluxes and carbon use efficiency. The results showed that China's forests had strong carbon sink capacity and high carbon use efficiency. The average annual gross primary production (GPP), ecosystem respiration (RE) and net ecosystem production (NEP) of forests was 1541 ± 92, 1155 ± 91 and 382 ± 37 g C m−2 a−1, and the average NEP:GPP, RE:GPP and NEP:RE was 0.25 ± 0.02, 0.74 ± 0.02 and 0.36 ± 0.04, respectively. Both carbon fluxes and use efficiency significantly varied with biomes, presenting higher values in subtropical and temperate forests than tropical and boreal forests. GPP and RE geographically decreased linearly with latitude increasing, while the NEP and its ratios to GPP and RE peaked at the mid-latitude. Large variances of carbon fluxes and use efficiency were mainly attributable to the regulation of mean annual temperature (MAT). MAT explained 40–54% of the variation in carbon fluxes, and 21–47% of variation in carbon use efficiency. Our result also indicated that carbon use efficiency was affected by stand age that presented an apparent decreasing trend from young to old-growth forests. The results advance our understanding about the variances and controls of carbon exchange and use efficiency and are valuable for regional carbon budget assessment.