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[A-5.1.1 Mechanisms at a Whole Plant Level]

[Contact Person]

NOUCHI, Isamu
National Institute of Agro-Environmental Sciences
3-1-1 Kannondai, Tsukuba, Ibaraki 305, Japan
Tel: +81-298-38-8161 , Fax: +81-298-8199

[Total Budget for FY 1993-1995]

25,718,000 Yen (FY 1995: 8,566,000 Yen)

[Abstract]

　Many studies have reported adverse effects of increased UV-B on crop growth and yield.
　Most of the studies, however, have been conducted in chambers or greenhouses, where plants are more sensitive to UV-B than in the field. In this study, we conducted enhanced UV-B irradiation to rice plants in a paddy field for 3 years 1993 - 1995. The UV-B enhancement was up to 1.7 times ambient UV-B_BE(biologically-effective UV-B) or 6.76 kJ m^-2 d^-1 for seasonal mean daily integral UV-B_BE. The UV-B irradiation caused a slight decrease in chlorophyll content, a slight increase in the UV-absorbing compounds, a substantial decrease in ascorbic acid, and an increase in dehydroascorbic acid, but no changes in glutathione content or anti-oxidative enzyme activities. The UV-B irradiation caused no significant changes in rice growth traits, e.g. plant height and biomass, but reduced the yield by up to 7%, which can be translated into a 1% yield loss by a 10% UV-B_BE increase. Rice yield loss will therefore be less than 2% with the projected UV-B_BE increase by 15%, which is caused by the peak ozone depletion of ca. 7% for the summer-autumn season in the northern midlatitudes.

[Key Words]

Ultraviolet radiation, Rice, Growth, Yield, Total ozone