Differential microbial roles in the organic layer and mineral soil determine radioactive cesium fate in forest ecosystems

Koarashi, Jun   ; Nagano, Hirohiko*; Nakayama, Masataka*; Atarashi-Andoh, Mariko  ; Nagaoka, Mika  

Radiocesium (Cs) contamination poses a long-term ecological challenge, particularly in forest ecosystems. The role of soil microorganisms in determining its fate remains insufficiently understood. This study presents a dynamic assessment of microbial Cs retention, focusing on the complex interplay among microorganisms, organic matter, and clay minerals within the organic layer-mineral soil system. Our results show that rapid microbial cycling sustains a potentially bioavailable Cs pool in the organic layer. This microbial involvement diminishes as Cs activity concentrations in the organic layer decline. In the mineral soil, minimal microbial Cs retention was observed, suggesting an indirect role in facilitating Cs immobilization by clay minerals. Notably, microbial Cs retention in the organic layer is regulated by Cs availability, independent of region, forest type, and time since deposition. These findings provide a unified explanation for observed differences in Cs persistence in organic layers between European and Japanese forests.