Effects of Root Temperature on Photosynthesis, Transpiration, Translocation and Distribution of ¹⁴C-Photoassimilates and Root Respiration in Tomato

Abstract

The effects of root temperature on photosynthesis, transpiration, root respiration, and translocation and distribution of photosynthetic assimilates in tomato plants were studied by steady-state feeding with ¹⁴CO₂. Plants at the seventh leaf stage which had grownunder constant 25° and 22°C air and root temperature respectively, were subjected to 22°, 15°, 10° and 5°C root temperatures.
1. With lowering of root temperature, except 5°C, the photosynthetic rate did not decreased significantly during 8 h of daylight, whereas the transpiration rate decreased significantly. Root respiration rate at higher root temperatures increased gradually during the day and maintained its level during the night with a small fluctuation, whereas, root respiration decreased proportionately to the decrease in temperature.
2. The amount of carbon respired by the root kept at 22°C plant was about three times higher than that evolved by plants held at 10°C. Export of ¹⁴C-photosynthetic assimilates from the 3rd leaf and its accumulation in the root decreased with lowering of root temperature.
Using these data, we discuss the significance of root respiration for the productivity of plants on the basis of carbon balance at the different root temperatures.