Abstract

A semi-closed system to label with ¹⁴C and trace photoassimilates under steady state conditions is described. It was used to elucidate the effects of night temperature on the carbon budget of tomato

The third leaf kept at 25 °C in 8 h light of 36 W m⁻¹ (PAR) assimilated 13·77 mg C . d⁻¹. By the end of the photoperiod, 46% of the carbon assimilate was exported to the sinks, out of which 27% was respired and 19% was accumulated in the sinks, respectively

The plants were then kept in the dark for 16 h at 15, 20, 25 and 30%C. The export in the night-time increased with night temperature, reaching 18–27% of the carbon assimilated. Thus, the total export in a whole day amounted to 63−72% of the carbon assimilated, out of which 35 and 42% were lost by respiration and 29 and 31% was accumulated in the sinks at 15 and 30 °C, respectively. Thus, accumulation in the sinks differed little with night temperature, while that in the source leaf, and hence the total accumulation, decreased with increasing night temperature

The export started early in the morning and was much greater in the light than in the dark. In addition, the day/night ratio of export was lower at higher night temperatures

The percentage distribution of ¹⁴C-assimilates to the lower parts decreased, while that to the upper parts increased with increasing night temperature. The calculated respiratory loss in individual sinks seemed to correspond to the distribution pattern of ¹⁴C-assimilates