In situ dynamics of recently allocated 14C in pasture soil and soil solution collected with Rhizon Soil Moisture Samplers

Abstract

Information on the dynamics of recently photo-assimilated carbon (C) allocated to roots and root-derived exudates in soils is scarce and experimentally difficult to obtain. We used Rhizon Soil Moisture SamplersTM (RSMS) placed at different depths in soil (20, 40, 80, 120 mm) to monitor short-term dynamics of root and root-derived C at the root–soil interface after 14CO2 pulse-labelling of pasture cores. At the 20 mm depth, 14C activity in soil solution peaked within 2 h of 14CO2 application. The peak of 14C activity took longer to appear and slower to disappear with increased depth. Negligible amounts of 14C as soluble exudates were found in the soil solution. The pattern of initial 14C activity in soil solution, allocation of recently assimilated 14C in roots, and root mass distribution with depth were closely related to each other. This suggested that the rapid appearance of 14CO2 in soil solution is more closely linked to root respiration of recent 14C-assimilates (transferred via shoots to roots) and/or to microbial decomposition of root-released 14C-assimilates than to transfer by diffusion of atmospheric 14CO2 through open soil surface to different depths in soil. The use of RSMS was an effective, simple, and non-destructive method to monitor the dynamics of root-derived 14C by in situ sampling of soil solution.