Layered structure significantly inhibits CO2 transfer through the depositional profile: as simulated by well-mixed vs. interlaid soil columns.

Depositional profiles often feature sorted layers with stratified porosity and water retention, but the vertical partitioning of CO2 production and transfer remain unclear. In this study, fine soil and coarse sand were refilled to form three layering patterns: Layer-Mix (soil and sand well-mixed), Layer-Thin (8 thin layers interlaid), and Layer-Thick (4 thick layers interlaid). Three doses of 13C-labelled glucose were respectively added to the top, middle, and bottom. The results show that the Layer-Thin and Layer-Thick cumulatively released 62% and 67% less CO2 than the Layer-Mix. The 13C-CO2 contributed 14.1~60.3% to the total CO2 released from the Layer-Mix, but was only responsible for 7.3~48.8% of that from the Layer-Thin and 7.0~37.0% of that from the Layer-Thick. The peaks of δ13C-CO2 of the two interlaid columns were lowered and lagged by 1~2 days, but the δ13C residue remaining in the soil were on average 3~6‰ more negative than that of the Layer-Mix. The 13C-CO2 contributed more to the total CO2 when the glucose was added at the top, but the δ13C-soil was 3‰ more negative when added at the bottom. Overall, the lagged outgassing and lower share of 13C-CO2 from the two interlaid columns did not match with the more negative 13C residue remaining in the soil. Such inconsistency collectively highlights that the interlaid layers did not inhibit the decomposition of 13C-labelled glucose (i.e., potentially abundant CO2 produced), but the low diffusivity of the fine layers significantly impeded CO2 transfer through the heterogeneously structured soil profile. [ABSTRACT FROM AUTHOR]