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Background and aims Fine roots can be functionally classified into an absorptive fine root pool (AFR) and a transport fine root pool (TFR) and their production, mortality and decomposition play a critical role in forest soil carbon (C) cycling. Different methods give significantly different estimates. However, how methodological difference affects AFT and TFR production, mortality, and decomposition estimates remains unclear, impeding us to accurately construct fine root C budgets. Methods We used dynamic-flow model, a model based on measurements of litterbags and soil cores, and balanced-hybrid model, a model based on measurements of minirhizotrons and soil cores, to quantify AFT and TFR production, mortality, and decomposition in a planted loblolly pine forest. Results Temporal changes in AFR and TFR production, mortality and decomposition estimates were generally the same between the two models. Annual production, mortality, and decomposition were comparable between AFRs and TFRs when measured using the dynamic-flow model but significantly higher for AFRs than for TFRs when measured using the balanced-hybrid model. Annual production, mortality and decomposition estimates using the balanced-hybrid model were 75%, 71% and 69% higher than those using the dynamic-flow model, respectively, for AFRs, but 12%, 6% and 5% higher than those using the dynamic-flow model, respectively, for TFRs. Model test showed that the balanced-hybrid model had greater accuracy than the dynamic-flow model in estimating AFR and TFR production, mortality and decomposition. Lower AFR estimates using the dynamic-flow model than using the balanced-hybrid model appeared to result from the underestimated AFR mass loss rate induced by the litterbag method. Conclusions The balanced-hybrid model is more reliable than the dynamics-flow model. Methodological difference has greater effects on AFR estimates than TFR estimates. Effects of methodological difference must be taken into consideration when quantifying fine root production, mortality and decomposition by functional groups. |
