Growth Responses of Rice Seedlings to Light Wavelengths : 1. Growth of seedlings exposed to various light wavelengths and variations caused by different growing conditions

Growth responses to light wavelengths and their variations under different growing conditions were examined using plastic films to filter sunlight, whose transmission of electromagnetic waved in the visible region was the same. 1. The greatest effect on plant height and dry matter production was induced by red light and that on the ratio of top dry weight to plant height and width of leaf blade was induced by blue light. A highly significant negative correlation between plant height and the transmission rate in the 400-500 nm region was observed. 2. Nitrogen, phosphorus, and chlorophyll content of tops were increased by blue light and TAC content was increased by red light. 3. Red light stimulated the photosynthetic activity but the increase of photosynthetic activity in seedlings grown under blue light was higher than under red light after the removal of films used for the light treatments. 4. The effect of red light on plant height and top dry weight was greater with the application of nitrogen fertilizer than with the addition of phosphorus and potassium ones. 5. With constant air temperature in the light period, the difference in the length of the 2nd leaf sheath between red and blue light became greater with increasing air temperature during the night period. 6. With less transmission in the visible region, the difference in chlorophyll content and plant height between red and blue light treated plants became less. 7. Although rice seedling growth responded to light wavelength differences, the degree of response varied under different growing conditions.