Effects of Temperature and Light on the Carbon Budget of Young Cucumber Plants Studied by Steady-State Feeding with14CO2

Abstract

cucumber seedlings was studied at irradiances of either 30 or 75 W m 2 (PAR) with a daylength of 8 h. The irradiance did not affect the relative distribution of 14C. assimilated by the source leaf between growth, respiration and export. In the range 15-30 °C rises in temperature generally increased the proportion of carbon exported. The average rate of carbon exported during the night was about half the rate in the day. About 45% of the exported carbon was lost by respiration. The distribution pattern of carbon exported during the day differed considerably from that of carbon exported during the night. The intensity of irradiance did not affect the proportion of labelled carbon recovered from the roots. Thus the decreased shoot/root ratio generally observed with increased irradiance is not directly controlled by carbohydrate supply. We found that the distribution patterns of exported 14C do not necessarily represent the real carbon distribution, due to differences in specific activity of imported carbon of individual organs. Consequently distribution patterns of 14C observed in experiments with one source leaf have to be considered with caution.