Priming is frequently overestimated in studies using 14C-labelled substrates due to underestimation of 14CO2 activity

The priming effect defined as an increased turnover of soil organic matter (SOM) upon organic substrate addition to soils has been investigated for decades, but its underlying mechanisms remain elusive. It has been shown that 14CO2 trapped in NaOH can be rapidly released from the solution when mixing small volume, low molar or highly CO2-saturated NaOH samples with scintillation cocktails. Therefore, liquid scintillation counting can substantially underestimate the 14C-activity of such samples. In this study, we explore the implications of this methodological shortcoming for priming studies.