The radiocesium (rCs) deposited onto forests of the Fukushima region was incorporated into the biogeochemical cycle of elements leading to its persistence within these ecosystems. To date, rCs partitioning has not reached an apparent steady state and its root uptake flux must still be accurately determined for long-term predictions of rCs behavior. Using its stable analogs (K and 133Cs) is a relevant approach to quantify this flux. Data were obtained from monitored even-aged Japanese cedar stands sampled in November 2013, 2014 and 2016. A mass balance approach was used for the determination of rCs, K and 133Cs annual recycling fluxes. Part of the results obtained in this study was used for parameterizing a dynamic rCs transfer model (cf. Gonze et al, IUFRO 2019). As expected, K and 133Cs concentrations remained constant over the 4-year period in all tree compartments. By contrast, rCs concentrations slowly decreased in all tree compartments over the same period. The measured [133Cs]/[K] ratios significantly varied between the biomass compartments, the discrimination between those elements being especially pronounced between living and corresponding senescing organs (e.g. outer and inner bark). It was also demonstrated that the root uptake fluxes of K and 133Cs were higher than internal translocation fluxes in both stands. We estimated the root uptake of 133Cs by applying the observed discrimination factors to each K apparent flux. This approach allows the use of K instead of 133Cs measurements that are poorly available for the calculation of rCs root uptake. Its efficiency will be discussed.