CARBON LOSS FROM THE ROOTS OF FORAGE RAPE (BRASSICA-NAPUS L) SEEDLINGS FOLLOWING PULSE-LABELING WITH (CO2)-C-14

The loss of organic materials from the roots of forage rape (Brassica napus L.) was studied by pulse-labelling 25-d- old non-sterile sand-grown plants with14CO2. The distribution of14C within the plant was measured at 0, 6 and 13 d after labelling whilst14C accumulating in the root-zone was measured at more frequent intervals. The rates of14C release into the rhizosphere, and loss of14CO2from the rhizosphere were also determined. These data were used to estimate the accumulative loss of14C from roots and loss of respiratory14CO2from both roots and associated microorganisms. Approximately 17-19% of fixed14CO2was translocated to the roots over 2 weeks, of which 30-34% was released into the rhizosphere, and 23-24% was respired by the roots as14CO2. Of the J4C released into the rhizosphere. between 35-51% was assimilated and respired by rhizosphere micro-organisms. © 1993 Annals of Botany Company.