Poplar males and willow females exhibit superior adaptation to nocturnal warming than the opposite sex.

The Salicaceae family consists of dioecious woody plants. Morphological and physiological species-related, sex-specific responses to nocturnal warming in these plants are seldom-reported. In order to explore the different responses of sex-biased species to nighttime warming, males and females of Populus cathayana and Salix paraplesia were used in this study. After 60 days of nighttime warming (+4 °C ambient nighttime conditions) in growth chambers, nighttime warming significantly (p ≤ 0.05) increased height growth rate, leaf proline content, leaf soluble protein content, and root soluble sugar content, while decreased biomass accumulation, photosynthesis, specific leaf area, and ATP levels in both species. Also, nighttime warming resulted in distorted chloroplasts and a greater starch accumulation in P. cathayana and S. paraplesia leaves. Moreover, sex-specific, nighttime warming responses were different, where P. cathayana males and S. paraplesia females exhibited lower aboveground to root mass ratios and higher root dry mass, net photosynthetic rates, stomatal conductance, total chlorophyll contents, specific leaf area, and lower foliar ATP, and less damage to mesophyll cells compared to the opposite sex. Therefore, P. cathayana males and S. paraplesia females exhibit superior adaptability to nighttime temperatures by enlarging their root systems, accumulating more carbohydrates, and adjusting osmotic substances to support their growth processes. Based on these results, it is predicted that P. cathayana males and S. paraplesia females will outperform the opposite sex under ongoing, rising nighttime temperatures in the future.