Effect of Low Soil Temperature on Weight Increase, Gas Exchange and Distribution of 14 C‐Assimilates in Seedlings of a Maize Hybrid

Seedlings of a maize hybrid sensitive to chilling initially grew in the growth chamber of the phytotron at 20/ 17°C (day/night) and after the formation of the fourth leaf, the soil temperature was lowered to 5°C. Under such growth conditions the dynamics of dry weight change, gas exchange and the distribution of 14 C‐assimilates in seedlings were examined. The low soil temperature inhibited daily growth of dry weight of whole seedlings more than their photosynthesis. Simultaneously, it was also responsible for a greater increase in dissimilative losses. During 37 hours (day‐night‐day), following exposure to 14 CO 2 , dissimilation in seedlings in cool soil (5°C) and in non‐chilling conditions amounted to 35.1 % and 23.4 % of assimilated 14 C (AC), respectively. At lower soil temperature relatively high dissimilative losses were observed on the first day after exposure (23.5 %), lower at night (9.9 %) and the lowest on the following day ‐ merely 1.7 % AC. Higher losses of 14 C under chilling conditions occurring on the first day were a result of limited photosynthetic refixation of 14 CO 2 At night, however, they were associated with a prolonged period of intensive translocation of assimilates to the stem. It was assumed that an excessive accumulation of assimilates in leaf blades might be an additional factor responsible for increased dissimilative losses at low temperature during the first twenty‐four hours. In the third period of measurements, as a result of a limited transport of 14 C, dissimilative losses were lower than in previous ones and were not dependent upon soil temperature.