Reconcilable differences: a joint calibration of fine-root turnover times with radiocarbon and minirhizotrons.

We used bomb-radiocarbon and raw minirhizotron lifetimes of fine roots (< 0.5 mm in diameter) in the organic layer of Norway spruce ( Picea abies) forests in southern Sweden to test if different models are able to reconcile the apparently contradicting turnover time estimates 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 about biases of both techniques - the classification of dead roots in minirhizotrons and the use of carbon 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 within 0.75 ± 0.10 yr, while the rest was turning over within 8.4 ± 0.2 yr. Bomb-radiocarbon and minirhizotron data alone give a biased estimate of fine-root turnover., The two-pool models allow a mechanistic interpretation for the coexistence of fast- and slow-cycling roots - suberization and branching for the serial-two-pool model and branching due to ectomycorrhizal fungi-root interactions for the parallel-two-pool model. [ABSTRACT FROM AUTHOR]