Objective To evaluating the physiological response and frost hardiness of two Quercus aliena cultivars ‘Qiuyun’ (red) and ‘Jinbangtiming’ (yellow) under low temperature in winter, and provide a theoretical reference for the promotion and application of new cultivars of Q. aliena in different regions.

Methods Branches and buds of two cultivars of Q. aliena from Beijing were collected at different stages. The frost hardiness of branches was determined by the conductivity method, and the anthocyanin content in branches and buds was determined by the hydrochloric acid-methanol method. The total phenolic content in branches was determined by the Folin phenol method, the non-tannin phenolic content was determined by the PVPP precipitation method, and the condensed tannin (CT) content was determined by the vanillin-hydrochloric acid method. The hydrolysable tannin (HT) content was obtained by subtracting the non-tannin phenolic content and CT content from the total phenolic content. The association between the frost hardiness of branches and anthocyanin and tannin content was analyzed.

Results (1) On December 19, 2023, the semi-lethal temperature (LT₅₀) values of ‘Qiuyun’ and ‘Jinbangtiming’ branches were −47.9 ℃ and −53.2 ℃, respectively. On January 5, 2024, the LT₅₀ values of ‘Qiuyun’ and ‘Jinbangtiming’ branches had shifted to −47.8 ℃ and −48.4 ℃, respectively. These results indicate that ‘Jinbangtiming’ exhibited higher frost hardiness compared to ‘Qiuyun’. (2) The anthocyanin content in Q. aliena branches increased as ambient temperatures decreased. On December 19, at the lowest recorded temperature, the anthocyanin content in ‘Qiuyun’ was significantly higher than in ‘Jinbangtiming’. Conversely, the anthocyanin content in buds followed an opposite trend. (3) During dormancy, the predominant type of tannin in Q. aliena branches was HT. When ‘Jinbangtiming’ entered dormancy, its HT was significantly higher than that of ‘Qiuyun’. At this stage, the HT and frost hardiness phenotype of the branches are consistent.

Conclusion (1) Both Q. aliena cultivars exhibit strong frost hardiness, with ‘Jinbangtiming’ demonstrating superior cold tolerance compared to ‘Qiuyun’. (2) The variation of frost hardiness between two cultivars of Q. aliena was associated with HT in the early dormant stage. High levels of HT in Q. aliena may play a critical role in enhancing the frost hardiness of branches. This study represents the first evaluation of the response of anthocyanin and hydrolysable tannin, as well as the frost hardiness, of two Q. aliena varieties under low winter temperatures. The findings preliminarily contribute significantly to understanding the mechanisms underlying frost hardiness in seedlings.