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Terrestrial ecosystems and soils are major actors in the Earth’s carbon cycle, and tightly linked to the evolution of atmospheric CO2 concentrations and climate change. Soils alone store several times more carbon than the atmosphere, and carbon cycling in soils could hence have substantial impact on atmospheric CO2 concentrations. To understand the timescales of carbon cycling in terrestrial ecosystems, radiocarbon measurements are an important tool. Yet, results from radiocarbon measurements have often conflicted with results other measurement techniques: In the study of root turnover, radiocarbon has yielded turnover times that are much longer compared to those attained by other methods, such as sequential coring or minirhizotrons. In the study of soil organic carbon turnover, radiocarbon has pointed to pools that cycle on centennial to millennial timescales. Empirical evidence, however, has suggested that individual compounds turn over more rapidly. This dissertation's overarching goal is to reconcile turnover models of roots and soil organic carbon with radiocarbon data by incorporating new process understanding into these models. The first part of the dissertation reconciles radiocarbon contents of fine roots with observations of root lifetimes from minirhizotrons. Previously root turnover had mainly been estimated by a one-pool model. This kind of model assumes an equal likelihood for root death throughout the lifetime of a root. Minirhizotron observations, however, have pointed to higher likelihoods of root turnover at the beginning of a root’s lifetime. In this thesis, a framework was developed that allows using minirhizotron and radiocarbon data in conjunction to estimate mean fine-root residence times. Survival functions from the field of survival analysis were used to estimate mean fine-root residence times from lifetime data of individual roots. Convoluting fine-root survival functions with the atmospheric radiocarbon bomb curve allowed performing a joint estimation of mean fine-root residence times ...