New dual in-growth core isotopic technique to assess the root litter carbon input to the soil

• Two independent methods coherently estimated the root-derived C input to the soil.
• The dual in-growth core technique corrected for δ13C changes unrelated to root inputs.
• The estimation of root-derived C input to the soil was significantly improved.
• The root-derived C input is an important fraction of NPP.

The root-derived carbon (C) input to the soil, whose quantification is often neglected because of methodological difficulties, is considered a crucial C flux for soil C dynamics and net ecosystem productivity (NEP) studies. In the present study two independent methods to quantify this C input to the soil were compared in a young forest plantation in Italy. Specifically, a mass balance approach to the soil C balance and a new dual in-growth core (IGC) isotopic technique that accounts for both root- and non-root-derived C inputs were compared. No statistically significant difference between the results obtained by the two methods was found (3.09 ± 0.50 vs 5.30 ± 2.92 Mg C ha− 1). Both estimates matched with the results obtained by other authors for similar ecosystems. The application of this new dual IGC isotopic technique has shown that the traditional IGC isotopic technique can lead to a significant overestimation (60% in the present study) of root C input to the soil as it doesn't take into account changes in the soil C isotopic signature due to factors other than root derived inputs. These include isotopic discrimination that could take place during the decomposition of original soil organic matter (SOM), the contamination due to dissolved organic C (DOC) leaching, or the C input via leaf litter. The proposed dual IGC isotope technique, taking into account the abovementioned non-root derived inputs seems to be a promising and reliable method to estimate root-derived C input to the soil in terrestrial ecosystems