Abstract: Field experiment was conducted to investigate the effects of nitrogen (N) supply on diurnal physiological characteristics in barley leaves at booting stage under enhanced UV-B radiation. The experiment was designed with two UV-B radiation levels, i.e. ambient (CK, 1.5kJ·m-2·h-1) and enhanced by 20% (1.8kJ·m-2·h-1), and two N supply levels, i.e. 30kg·ha-1(low) and 150kg·ha-1(high), and performed at the station of agricultural meteorology, Nanjing University of Information Science and Technology. The results showed that, enhanced UV-B radiation decreased net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductivity (Gs) and water use efficiency (WUE) by 44.6%, 21.8%, 17.8% and 28.4% under high N level, respectively, and reduced by 49.5%, 11.8%, 12.9% and 42.7% under low nitrogen level, respectively. The findings suggested that enhanced UV-B radiation depressed photosynthesis and water use efficiency in barley leaves, increasing N supply could alleviate the damage to net photosynthetic rate from enhanced UV-B radiation，but not to transpiration rate and stomatal conductivity. Based on the diurnal change of intercellular CO2 concentration in relation to net photosynthetic rate, it indicates that N supply and enhanced UV-B radiation impacted photosynthesis directly by the process of photosynthetic reaction, not by stomatal conductivity in barley leaves at booting stage.

Key words: UV-B radiation, Nitrogen fertilization, Diurnal physiological characteristics, Barley