## 2 Results and Discussion  
### Effect of Attenuated UV Radiation on Three Major Classes of Volatiles  
Volatile compounds are divided into three classes according to their biosynthetic pathways. These three classes of volatiles showed the similar variation trends in the developing grapes under these two experimental vintages. However, great differences were observed in their concentration (Figure 2). For example, the concentrations of amino acid-derived and isoprenoid-derived volatiles in the 2010 vintage were almost two or even more times higher than those in 2009. Moreover, a total of 102 volatile compounds were identified in the 2010 vintage, whereas only 72 volatiles were present in the 2009 vintage (Supplementary Table S1). The difference in the composition and concentration of volatiles between these two year vintages might result from the distribution of rainfall amount during the growing season. Meteorological record from the local meteorological station showed that the accumulative rainfall from June to September was 226.6 mm and 273.9 mm in 2009 and 2010, respectively. The rainfall mainly occurred in July, 2009, with a rainfall amount of 112.4 mm. However, in 2010 the monthly rainfall amount was relatively homogeneous. It was also observed that the sunshine hours, average air temperature, and average daily temperature difference were similar between these two vintages. Except for benzenoids, no differences were observed in the composition of the other volatiles in the same vintage. Isoprenoid-derived volatiles tended to decline during grape development in both vintages, and the lowest level was observed at harvest stage for both treated grapes and the control in 2009, but in 2010, their total concentration in the treated grapes slightly increased at harvest. Except that the UV1-B- treated grapes at 5 waf in 2010 showed higher concentration of isoprenoid-derived volatiles than the control (Figure 2), no significant differences were observed between the attenuated UV-treated grapes and the control in the other stages across the two vintages. This implied that the impact of attenuated UV radiation on the isoprenoid metabolism in grape berries could be limited. The concentration of amino acid-derived volatile compounds increased with the berry maturation, except for a slight decline at 14 waf. At harvest, the attenuated UV radiation treatment with both polyester film A and B significantly enhanced the accumulation of amino acid-derived volatiles in these two vintages. The UV3-B treated grapes (attenuated UV from the onset of veraison to harvest) contained greater level of amino acid-derived volatiles compared to the control (Figure 2). These results indicatedthat the attenuated UV radiation intensity and treatment stages play important roles in affecting the metabolisms of amino acid-derived volatiles in grapes. Fatty acid-derived volatile compounds accounted for over 80% of the total concentration. Overall, it showed an increasing trend, and then a decrease in the development stages of grapes. Apart from the grapes at 5 waf in 2009, the attenuated UV-radiation treated grapes had lower level of fatty acid-derived volatiles compared to the control. Particularly, the UV1 treatments with both polyester film A and B reduced the accumulation of these volatiles in both of the vintages (Figure 2). This indicated that reducing UV radiation might down-regulate the synthesis of fatty acid derivatives. The UV1-B treated grapes displayed the most obvious difference in accumulation of amino acid-derived and fatty acid-derived volatiles, followed by UV1-A treated grapes and then the control. This indicated that UV radiation influence was dose-dependent. The above analyses indicated that the effects of the attenuated UV1 radiation were similar between these two year vintages. Moreover, the attenuated UV radiation treatments with film A and B also showed similar effects on the alteration of volatile metabolisms.