Abstract: Field simulating experiment with barley was conducted to investigate the effects of silicon（Si）supply on diurnal variations of net photosynthetic rate（Pn），transpiration rate（Tr），stomatal conductivity（Gs），intercellular CO2 concentration（Ci）and water use efficiency（WUE）under elevated UVB radiation The experiment was designed with two UVB radiation levels，ieambient（A，1.5kJ·m-2）and elevated UVB（E，1.8kJ·m-2），and two Si supply levels，ieSi0（0kg·ha-1 SiO2）and Si1（150kg·ha-1 SiO2）The results showed that，compared with ambient UVB radiation，elevated UVB radiation decreased net photosynthetic rate，transpiration rate，stomatal conductivity and water use efficiency by 23.13%，7.66%，1.07% and 16.38% under Si0 level，respectively，and reduced by 10.52%，5.71%，3.77% and 12.15% under Si1 level，respectively This finding suggested that elevated UVB radiation depressed net photosynthetic rate，transpiration rate and water use efficiency in barley leaves，increasing Si supply could alleviate the damage to net photosynthetic rate from elevated UVB radiation，but not to transpiration rate and stomatal conductivity This research will be helpful in further investigating the effect of Si supply on barley yield and quality under elevated UVB radiation.

Key words: UVB radiation, Silicon supply, Barley, Photosynthesis, Transpiration