Global environmental change and ecophysiology of rice : fundamentals of sustainable food production.

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This work was focused to develop the fundamentals of crop production techniques predicted for the future climatic change (high CO_2, hothouse earth). Used materials was a japonica paddy rice (Oryza sativa L.cv.Nipponnbare) because this crop species sustains sbout half of world pupulation as a food. The important characteristics in the production processes (photosynthesis, respiration, assimilate translocation, tillering, leaf area, yield components, mineral nutrition, etc.) were examined under simulated growth environment (ambient and high levels of CO_2 [350vs.700ppm] and temperature with and without sufficient nutrient supply). Following results were obtained ;(1) By the review process of preceding studies on high CO_2 and plant production, the investigator found many problems unsolved and/or unexamined. (2) Chloroplast structure of the leave was deformed by elevated CO_2 due to surpluss production of starch granule. This sometimes coupled with partial down-regulation of photosynthesis. (3) Leaf photosynthesis was affected greatly by light and vapor saturation deficit and preferred strong light and moderately higher moisture and temperature under high CO_2 conditions. (4) Successive measurements of photosynthesis and respiration during the growth revealed that the enhancement of dry matter production by high CO_2 was attributed to the promotion of photosynthesis coupled with active respiration, at least in vegetative stages. (5) Biomass production was substantially influenced by both nitrogen and phosphorus and their use efficiency in production process increased under high CO_2. (6) High CO_2 promoted paddy yield trough the increments of both the number of panicles per plant and the number of grains per panicle. However, grain quality tended to decline.Based on the above results and preceding reports, the investigator discussed future climate change and rice production.