Estimation of the rates of mass carbon transfer by leaves of sugar beet

Estimates of the rate of translocation of carbon, T, from sugar beet leaves were made from simultaneous determinations of CO2 exchange and dry weight change. For an illuminated leaf in a constant environment, T increased to a maximum during the first 2 h and was constant for the next 10 h. On darkening, T decreased rapidly in the first 2 to 4 h to a constant minimal value which could continue for as long as 24 h. The average value of T for nine leaves in the light was 4.2 ± 0.4 mg C dm−2 leaf surface h−1, while in the dark the average value for five leaves over 10 h was 1.2 ± 0.2 mg C dm−2 h−1. Generally T was about three-quarters of the net rate of photosynthetic carbon fixation.