Carbon Loss from the Roots of Forage Rape (Brassica napus L.) Seedlings Following Pulse-labelling with 14CO2

Abstract

The loss of organic material from the roots of forage rape (Brassica napus L.,) was studied by pulse-labelling 25-d-old non-sterile sand-grown plants with 14CO2. The distribution of 14C within the plant was measured at 0, 6 and 13 d after labelling whilst 14 C accumulating in the root-zone was measured at more frequent intervals. The rates of 14C release into the rhizosphere, and loss of 14CO2 from the rhizosphere were also determined. These data were used to estimate the accumulative loss of 14C from roots and loss respiratory 14CO2 from both roots and associated micro-organisms. Approximately 17-19% of fixed 14CO2 was translocated to the roots over 2 weeks, of which 30-34% was released into the rhizosphere, and 23-24% was respired by the roots as 14 CO2. Of the 14C released into the rhizosphere, between 35-51% was assimilated and respired by rhizosphere micro-organisms.