## 4 Discussion
Other studies also showed that a large temperature difference between day and night would increase the content of the total soluble solids in grape berries [59], and when the temperature was higher than 20 \({}^{\circ}\)C, the titrating acid of different grapes will be reduced [60], which showed that the decomposition rate of the organic acids in fruits could be higher than those in the treatment. The effects on the flavonoid compounds in grape berries and wines between treatments were similar. Covering purslane increased the total concentrations of anthocyanins by 2.3% and 2.7% in the berry skins, and 12.6% and 1.8% in the final wines, respectively in the years 2018 and 2019. Covering purslane also increased the color parameters of wines and improved the color quality of the wine samples. These findings were similar to the results of [PERSON] et al. [51]. The increase in the anthocyanin concentration in covering purslane berries might be a result of the decreased berry weight because there was no significant difference between the control and the treatment of covering purslane in the anthocyanin contents of each berry. Although the general view was that the increased exposure would result in the enhanced anthocyanin biosynthesis, there was a point at which the temperature load will begin to have a negative impact [61]. The effect of covering purslane on the flavanols in berries and wine was similar [62]. For the two consecutive years, the flavanols of the treatment of covering purslane in grape seeds were reduced, but the effects were not significant. It was speculated that the reflection might be weakened and changed the composition of light by the grass covering between rows [63]. However, there was no significant effect on the wines in their study. The authors presumed that it was mainly due to the small-scale fermentation having a shorter time of maceration. And only a small part of the flavanols in the grape seeds entered the wines through the part of maceration. In the present study, while the decreased solar radiation was an unfavorable factor for the anthocyanin biosynthesis, a little high-temperature stress in covering purslane bunches was beneficial for the anthocyanin biosynthesis. And more, the combined effects resulted in no significant difference in the anthocyanin content of each berry. However, an increase in flavonoids was observed in both berries and wines from the treatment of covering purslane in 2018. It was well known that the primary function of flavonoids was to serve as a UV filter, because they absorb light in the 280-330 nm range to protect the plant tissues from UV damage [44; 64]. Furthermore, covering purslane increased the contents of the norisoprenoids in grape berries and wines, enhanced the floral, fruity, and caramel flavors in the wines, and also improved the aroma quality of the wines, which had a certain positive effect on improving the aroma quality of the wines. This was the same as the results of [PERSON] et al. [65]. And the results were mainly due to the competition of plants after covering crops, which caused water stress, and then increased the accumulation of the norisoprenoids precursor substances, which increased the content of norisoprenoids [66]. To sum up, the treatment of covering crops, especially the purslane, could regulate the microclimate of the vineyards, which did not affect the yield of grapevines, and it reduced the total soluble solids (TSS) in the grape berries and increased their tittatable acidity (TA). Therefore, covering purslane successfully delayed the berry ripening in the semi-arid wine regions of northwest China. Covering purslane there increased the contents of anthocyanins, flavonoids, and norisoprenoids substances in grape berries somehow and increased the color value of the resulted wines, as well as the contents of anthocyanins and flavonoids in their wines, and enhanced the floral, fruity and caramel tastes.