Effect of rare earth oxide labeling and sieving processes on Andisol aggregate turnover and organic carbon dynamics

Rare earth element (REE) oxides serve as effective tracers to track aggregate dynamics. However, the impact of labeling and sieving processes on aggregate and organic matter dynamics remains uncertain. This study aimed to determine the effect of the labeling and sieving processes on soil aggregate and organic carbon dynamics.

Dry and wet sieved aggregates from a Japanese typical Andisol were labeled with REE oxides. REE oxides concentrations and soil organic carbon fractions were measured during the 28-day incubation period to calculate aggregate transformation paths and soil organic carbon dynamics.

The findings demonstrated that REE oxides are effective tracers to track Andisol aggregate turnover. The labeling and sieving processes showed significant positive effect on aggregate turnover. During incubation, wet sieved macroaggregates displayed more transformation than dry sieved aggregates (5.26% ~ 7.24% vs. 11.03% ~ 12.81%), reflecting a higher turnover rate of macroaggregates resulting from wet sieving relative to dry sieving. Regarding organic carbon fractions, the labeling process significantly affected dissolved organic carbon (DOC), microbial biomass carbon (MBC), and free particulate organic matter (fPOM). Additionally, the degree of interference was linked to the sieving processes, with MBC and fPOM content significantly lower following wet sieving. This effect persisted during incubation, except for fPOM content, which exhibited a rapid increase accompanied by a decrease in occluded particulate organic matter (oPOM) content following the wet sieving method.

Our results demonstrate that the effects of labeling and sieving processes should be considered when analyzing the relationship between aggregate turnover and organic carbon with REE oxides tracers.