Abstract: The aim of the present study is to investigate the responses of the contents of leaf chlorophyll, soluble substances and UV-B absorbing compounds of foxtail millet (Setaria italica (L.) Beauv.) at flowering stage to enhanced UV-B radiation treatment and whether the possible effect varied with nitrogen supply. The plants of foxtail millet were fertilized at two different nitrogen supply levels (1.88 and 15 mmol·L^-1) from the beginning of jointing stage and stressed by an enhanced UV-B radiation treatment (14.7 μW·cm^-2) from the beginning of heading stage. The results showed that chlorophyll content and soluble protein content decreased evidently, while UV-B absorbing compounds content increased in leaves of foxtail millet under the lower nitrogen supply level compared to the group under the higher nitrogen supply level during the treatment period, with or without enhanced UV-B radiation. Chlorophyll content from the beginning to middle of flowering stage and soluble protein content at the beginning of flowering stage in leaves of foxtail millet under the higher nitrogen supply level were more sensitive to the enhanced UV-B radiation treatment than under the lower nitrogen supply level. Leaf soluble sugar content was not sensitive to the enhanced UV-B radiation treatment, whereas it was significantly affected by nitrogen supply level from the middle to the end of flowering stage. The study indicated that the lower nitrogen supply level could improve the resistance of plants against UV-B radiation by promoting the accumulation of UV-B absorbing compounds in leaves of foxtail millet at flowering stage; however, a reasonable range of nitrogen supply level should be adopted to balance the requirements between reproductive growth and improvement of the resistance to UV-B radiation.

Key words: ¹³C, light environment, photosynthetic characteristics, photosynthetic products, flue-cured tobacco