Objective  This study aimed to investigate the physiological responses of Phyllostachys aureosulcata and its varieties to natural low temperatures in Beijing and to make a comprehensive evaluation of their cold tolerance.

  Method   Phyllostachys aureosulcata and its varieties (Phyllostachys aureosulcata f. spectabilis, Phyllostachys aureosulcata f. aureocarlis) were used to analyze their chlorophyll content, osmoregulatory substances, antioxidant system indicators and endogenous hormone characteristics, the entropy-weighted TOPSIS method was used to comprehensively evaluate the cold tolerance of the three varieties.

  Result  The chlorophyll content of Phyllostachys aureosulcata was higher than that of its varieties. Phyllostachys aureosulcata f. aureocarlis had the highest malondialdehyde (MDA) content, but its antioxidant enzyme (SOD, POD, CAT) activities were lower than those of the other two varieties. The soluble sugar and soluble protein contents in young bamboo leaves were significantly higher than those of the other two varieties. The chlorophyll content, the activity of SOD and POD of Phyllostachys aureosulcata f. spectabilis decreased significantly with increasing age, and the changes in osmotic substances content were not significantly different (P > 0.05). The content of the three osmotic substances was significantly higher in young Phyllostachys aureosulcata f. aureocarlis than in the old ones, and the difference in the indexes of the antioxidant system between the two age stages of Phyllostachys aureosulcata reached a significant level (P < 0.05). The ABA/GA₃ ratios of the three varieties were ranked as follows: Phyllostachys aureosulcata f. spectabilis, Phyllostachys aureosulcata, Phyllostachys aureosulcata f. aureocarlis. ANOVA and correlation analysis showed that chlorophyll a, chlorophyll b, total chlorophyll, soluble sugar, soluble protein, MDA, POD, CAT, and SOD differed significantly (P < 0.05) among varieties, and all indicators were correlated with each other to different extents.

  Conclusion  Variety influenced the cold hardiness of Phyllostachys aureosulcata and its varieties most, followed by the interaction between variety and age. Based on the entropy-weighted TOPSIS comprehensive evaluation method, MDA content accounted for the greatest weight (35.44%) in the cold hardiness indicators, followed by the activities of POD and SOD. Evaluation of the 11 indicators showed that Phyllostachys aureosulcata f. aureocarlis was the most cold resistant variety. The ratio of ABA/GA₃ indicates that the hormones may regulate cold tolerance in bamboo by crosstalk.