Abstract: Population with a biased sex ratio and sexual difference in functional traits may have negative effects on population dynamic in dioecious species. However, few studies have examined the sexual difference in the endangered dioecious species. In this study, we investigated the sex ratio and the sexual differences in morphology and photosynthetic nutrient and water use efficiency in the leaves of adult Cercidiphyllum japonicum Sieb. et Zucc. in Xiaozhaizigou National Nature Reserve in western Sichuan Province. Our results showed that the sex ratio was biased towards females (F/M=1.97; χ²=4.46, P=0.035). The diameter at breast height, crown width, maximum photosynthetic rate, apparent quantum yield, maximum carboxylation efficiency, specific leaf area, leaf nitrogen content, and use efficiencies of water, nitrogen and phosphorus of females were 44.50%, 27.94%, 20.11%, 50%, 21.14%, 14.32%, 14.86%, 158.7%, 19.74% and 28.03% higher than those of males, respectively, while stomatal conductance, intercellular CO₂ concentration, transpiration rate, and light compensation point of females were 20.83%, 24.61%, 56.11% and 44.44% lower than those of males, respectively. These results indicated the existence of sex ratio bias and sexual dimorphism in ecophysiological traits, which may cause its endangerment. The sexrelated difference should be considered in the future study of endangered mechanisms in dioecious species.

Key words: monoculture agriculture, ecological imbalance, sustainable security agriculture, organic agriculture.