EFFECTS OF ROOT TEMPERATURE ON PHOTOSYNTH ESIS, TRANSPIRATION, TRANSLOCATION AND DISTRIBUTION OF C-14 PHOTOASSIMILATES AND ROOT RESPIRATIONIN TOMATO

The effects of root temperature on photosynthesis, transpiration, root respiration, and translocation and distribution of photosynthetic ass imilates in tomato plants were studied by steady-state feeding with (C O2)-C-14. Plants at the seventh leaf stage which had grown under const ant 25-degrees and 22-degrees-C air and root temperature respectively, were subjected to 22-degrees, 15-degrees, 10-degrees and 5-degrees-C root temperatures. 1. With lowering of root temperature, except 5-degr ees-C, the photosynthetic rate did not decreased significantly during 8 h of daylight, whereas the transpiration rate decreased significantl y. Root respiration rate at higher root temperatures increased gradual ly during the day and maintained its level during the night with a sma ll fluctuation, whereas, root respiration decreased proportionately to the decrease in temperature. 2. The amount of carbon respired by the root kept at 22-degrees-C plant was about three times higher than that evolved by plants held at 10-degrees-C. Export of C-14-photosynthetic assimilates from the 3rd leaf and its accumulation in the root decrea sed with lowering of root temperature. Using these data, we discuss th e significance of root respiration for the productivity of plants on t he basis of carbon balance at the different root temperatures.