The dynamics of glucose-derived 13C incorporation into aggregates of a sandy loam soil following two-decade compost or inorganic fertilizer amendments

Soil aggregates play a central role in the soil organic carbon (SOC) sequestration. To understand the stabilization process of exogenous easily decomposable organic C in soil and aggregates, 13C-glucose was supplied to arable soils following a 20-year application of compost (CM), inorganic NPK (NPK) and a control (no fertilizer, CK). Soil was fractionated into large macroaggregate (>2000 μm), small macroaggregate (250-2000 μm), microaggregate (53-250 μm), silt fraction (2-53 μm) and clay fraction (<2 μm) by wet-sieving. The dynamic variation and the distribution of glucose-derived 13C in soils and aggregates were monitored during the 30-day incubation using the 13C stable isotopic technique. The amount of glucose-derived 13C remaining in soils decreased from 61.6-76.9% (day 3) to 27.8-53.1% (day 30). In contrast, the proportion of glucose-derived 13C remaining in aggregates during fractionation to that in soil increased from 13.2-29.4% (day 3) to 32.5-39.3% (day 30) and was ranked as: CCM > CNPK > CCK over the entire incubation. The content of glucose-derived 13C in large and small macroaggregates decreased gradually, but steadily increased in the silt and clay fractions in all treatments over the 30-day incubation period. However, glucose-derived 13C in microaggregates remained at the constant level during the incubation. Our findings indicate that the proportion of 13C protected from dissolving in water during wet-sieving increased with the incubation, and the exogenous easily decomposable organic C could be more effectively maintained in organic C-rich soil (CM) than in organic C-poor soil (CK or NPK). Clearly, glucose-derived 13C was sequestrated and stabilized gradually in soil by redistribution from macroaggregates to silt and clay fractions.