Effect of rise in carbon dioxide concentration on transpiration and photosynthesis, water utilization efficiency and micro weather of paddy field.

Experimental method: Experiment for increasing the concentration of outdoor atmospheric carbon dioxide (FACE - CO₂). Controlled the carbon dioxide concentration 1.5 times the current level.

FACE = Free Air Concentration Enrichment

Measurement items: transpiration and photosynthetic rate of rice leaves, micro-meteorological environment of paddy field, plant body area, plant yield.

Development tools: Paddy field multilayer weather model (incorporating rice response due to increase the carbon dioxide concentration)

RESULTS: As the concentration of carbon dioxide increases, pore conductance (indicator of pore opening degree) of individual leaves decreases, and the photosynthetic rate of individual leaves increases. However, at a plant community level, it was confirmed that the photosynthetic rate of the community could decrease due to attenuation of light energy caused by increase in leaf area at lower part of the plant community and aging of leaves by acceleration of growth stage. As a consequence of these results, it was demonstrated that the water utilization efficiency (= photosynthesis rate / evapotranspiration rate) of the community may rise slightly.

Influence of air pollution (increase in ozone concentration) on growth and yield of rice and wheat

Experimental method: Experiment of increasing ozone concentration in outdoor atmosphere (FACE - O ₃). Controlled the ozone concentration to 1.5 times the current level.

Measurement item: transpiration / photosynthetic rate of rice leaves, micro-meteorological environment of paddy field, plant body area, plant yield.

Developed tool: Paddy field multilayer weather model (crop response due to rising ozone concentration = incorporate ozone dose response).

Ozone dose response function by varieties

Results: FACE experiments on four varieties of rice and in three varieties of wheat resulted in a decrease in pore conductance of individual leaves and photosynthetic rate of individual leaves. This response could be expressed by the relationship of ozone absorption integration through pores. However, the effect was different depend on the varieties. For example, in case of a hybrid rice developed for high yields has a lower photosynthetic rate and a lower yield than a conventional Chinese cultivar rice due to the increased in ozone concentration. The ozone dose response function for each variety developed in this study was able to reproduce the influence of ozone concentration increase for each variety.