Fundamental Studies on Optimization of Environment in Plant Production

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Environmental effects on whole plant water relations, root physiological functions and translocation of photoassimilates were analyzed by using cucumber plants and sweet potato plants with the view of integrating data base for environmental optimization in plant production. Evaporative demand (ED) and its impact (Imp) on plant water relations were defined quantitatively by using environmental factors and leaf characteristics. Dynamics of ED and Imp directly related to plant water balance, stomatal movement, leaf growth, dry matter production and water use efficiency, and this suggests the applicability of control of ED and Imp for optimizing plant water relations. An environment control system of airtight hydroponics was newly developed for measurements of root respiration and water uptake rates and for ^<18>O_2tracing. Root water uptake in O_2-deficient nutrient solution was promoted with aerial O_2 in darkness, and appeared simultaneous in dynamics with root respiration. It was found that ^<18>O_2 applied to aerial environment is respired by root respiration in O_2-deficient nutrient solution. These facts suggest that aerial O_2is transported through leaves for root respiration in cucumber plants grown in an O_2-deficient root environment, and this results in improvement of water uptake. On translocation of photoassimilates, two culture systems were newly developed for analyzing environmental effects on sink-source relationships : (1) a sand culture system where sink and source environments can be controlled independently : (2) a solution-air culture system in which storage sink and utilization sink are separated by keeping tuberous root in air space and fibrous roots in nutrient solution. On those systems, the optimum temperature and humidity conditions for tuberous root growth were examined. The methodology newly established can be helpful for integrating quantitative data base for optimization of plant environments.