∙ We used bomb-radiocarbon and raw minirhizotron lifetimes of ﬁne roots (< 0.5 mm indiameter) in the organic layer of Norway spruce (Picea abies) forests in southern Sweden totest if different models are able to reconcile the apparently contradicting turnover time esti-mates from both techniques.
∙ We present a framework based on survival functions that is able to jointly model bomb-radiocarbon and minirhizotron data. At the same time we integrate prior knowledge aboutbiases of both techniques – the classiﬁcation of dead roots in minirhizotrons and the use ofcarbon reserves to grow new roots.
∙ Two-pool models, either in parallel or in serial setting, were able to reconcile the bomb-radiocarbon and minirhizotron data. These models yielded a mean residence time of 3.80 ± 0.16 yr (mean ± SD). On average 60 ± 2% of ﬁne roots turned over within0.75 ± 0.10 yr, while the rest was turning over within 8.4 ± 0.2 yr. Bomb-radiocarbon andminirhizotron data alone give a biased estimate of ﬁne-root turnover.
∙ The two-pool models allow a mechanistic interpretation for the coexistence of fast- andslow-cycling roots – suberization and branching for the serial-two-pool model and branchingdue to ectomycorrhizal fungi–root interactions for the parallel-two-pool model.