Effects of methodological difference on fine root production, mortality and decomposition estimates differ between functional types in a planted loblolly pine forest

Background and aims Fine roots can be functionally classified into an absorptive fine root pool (AFR) and a transport fine root pool (TFR). Different methods give significantly different fine root production, mortality and decomposition estimates. However, how methodological difference affects fine root estimates has not been assessed by functional type, impeding accurate construction of 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 estimates in a planted loblolly pine forest. Results Annual production, mortality, and decomposition were comparable between AFRs and TFRs when measured using the dynamic-flow model ( P > 0.1) but significantly higher for AFRs than for TFRs when measured using the balanced-hybrid model ( P < 0.05). 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. The balanced-hybrid model yielded more reliable AFR and TFR estimates than the dynamic-flow model by directly measuring fine root production and mortality dynamics. Conclusion The balanced-hybrid model has greater estimation accuracy than the dynamics-flow model. The methodological difference has greater effects on AFR than TFR estimates. The choice of method is critical for quantifying AFR and TFR contributions to fine root C budget.