Respective horizon contributions to cesium-137 soil-to-plant transfer: A pot experiment approach

The OAh horizons in forest acid soils are reported to fix more radiocesium than the mineral horizons beneath and organic horizons above them. We determined the respective contributions of the Of, OAh, Ah, and Bw horizons in an acid brown soil to the total ¹³⁷Cs soil-to-plant transfer by using young spruce plants [Picea abies(L.)H. Karst.] grown on reconstituted micro-pedons in which these respective horizons were contaminated by carrier-free ¹³⁷Cs. The plants were grown in a greenhouse at 20°C during a period of 5 mo. The respective contributions to the ¹³⁷Cs soil-to-plant transfer were 92.71% in Of, 0.18% in OAh, 3.28% in Ah, and 3.83% in Bw. The very high contribution of Of was due to its high organic matter (OM) content, while the very low contribution of OAh was related to Cs⁺ fixation by vermiculitic clay minerals. The higher ¹³⁷Cs transfer from Ah and Bw vs. OAh was probably associated with Al interlayering of vermiculite. Our data suggest that plant roots and soil vermiculite acted as competitive for ¹³⁷Cs in the acid brown soil.