Phenolic compounds are important secondary metabolites of wine grape, which have an important influence on the quality of grape and wine. In this study, the differences and genesis of phenolic substances in grape skins among different altitudes were studied combined with soil and climate factors, so as to provide a theoretical basis for the planting management of wine grapes at high altitudes region.

In the present research, Merlot wine grape was used as the test material. For three consecutive years (2020, 2021 and 2022), the differences of total phenols, flavonoids, tannins, total anthocyanins, the content of individual and non-individual anthocyanin components in grape skins at two altitudes (2 181, 2 300 m) at maturity stage were analyzed. Meanwhile, climate factors such as light, temperature and humidity at different altitudes were monitored during grape development, and the influences of climatic factors on phenolic substances of grape skins were analyzed.

There were no significant differences in the main mineral nutrients of the soils of the two altitude vineyards, and some differences in climatic factors, such as light, UV intensity, temperature and humidity. Altitude had a significant effect on the content of phenolic substances in grape skins. In the years of 2020-2022, the higher altitude was conducive to the accumulation of phenolic substances in grape skins. the content of total phenols, total tannin, total anthocyanins, most of the individual anthocyanins and the quercetin in berry skins were higher at the altitude of 2 300 m; compared with that at 2 181 m, the content of total tannin in grape skins at 2 300 m increased by 56.27%-174.49%. The flavonoid content at 2 181 m altitude were significantly higher than that at 2 300 m, with an increase of 32.25% to 79.48%. OPLS-DA analysis showed that, the main different compounds of phenolic compounds between the two altitudes were total tannin (TTC), total flavonoids (TFo), malvidin-3-glucoside (Mv), malvidin-3-acetly-glucoside (Mv-Ace), cyanidin-3- glucoside (Cy), and peonidin-3-glucoside (Pn). Grey correlation analysis showed that day-night temperature difference in grape growing season had a great effect on the content of total phenols and total flavonoids in grape skins. The content of total anthocyanins, individual anthocyanins and quercetin in skins were significantly affected by light and ultraviolet intensity. The content of three anthocyanins (Pt, Pn-Ace and Pn-Cou) and quercetin were mainly affected by the light intensity during grape veraison (July).

The climatic conditions of different altitudes, especially day-night temperature difference, light and ultraviolet intensity were the main factors causing the differences of phenolic content. The larger day-night temperature difference, stronger light and ultraviolet intensity at higher altitude were conducive to the accumulation of phenolic substances in grape skins.