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Recent syntheses of elevated CO2 (eCO2) experiments provide critical information to quantify the effects of rising CO2 on vegetation. However, although the eCO2 effect on aboveground biomass (βAGB) and soil carbon pool (βCsoil) have been estimated, little has been known about the eCO2 effect on total net primary production (βTNPP) - the sum of above and belowground - due to the difficulties of measuring NPP in eCO2 experiments. As a preliminary analysis of βTNPP, we ran a thorough meta-analysis of global eCO2 experiments and found that (1) Most of the experiments reported a larger βTNPP than βAGB (2) Most of the experiments reported a larger eCO2 effect on belowground (roots) biomass (βBGB) than total biomass (βTB) (for AM mycorrhizal association only) (3) On average, seedling experiments reported a larger βAGB than mature vegetation experiments. Aiming to improve estimates of βTNPP we hypothesized that βAGB could be underestimated due to short experimental time relative to biomass mean residence time, i.e., that βAGB increases with experimental time. We proposed a set of simple first kinetics equation to derive βTNPP with consideration of the imbalance between βBGB and βTB. We first validated the equations on experiments reporting both productivity and biomass before applying to other experiments. We found that, after the application, (1) On average, βTNPP of seedling experiments are insignificantly different to βTNPP of mature vegetation experiments (2) Compared with βAGB, the relative importance of mycorrhizal on βTNPP decrease, and soil CN ratio and soil phosphorus became the most important predictors. (3) The disagreement between experiments and models was smaller for βTNPP than for βAGB.