Abstract: [Objective] In this study, dynamic patterns of sex-specific water and nitrogen use efficiencies in male and female plants of dioecious Litsea cubeba were analyzed. The result provides a theoretical basis for understanding of the dynamic changes of resource allocation of dioecious plants.[Method] The nutrient content (carbon and nitrogen content, the ratio of carbon and nitrogen (C/N)), water use efficiency, as inferred from leaf carbon isotope composition (δ¹³C), and nitrogen use, estimated by leaf nitrogen isotope composition (δ¹⁵N) were measured in male and female plants during 105 and 165 days after flowering (DAF).[Result] 1) The mean leaf δ¹³C values of female and male plants were -29.38‰ and -28.08‰. Leaf δ¹³C values of both male and female plants were significantly affected by sex and development period. Leaf δ¹³C values of the female plants were all lower than the male plants for the five periods. Leaf δ¹³C values of both male and female plants were constantly decreased during the development period. 2) The mean leaf δ¹⁵N values of the female and male plants were 1.90‰ and 2.95‰. Sex and development period also had significant effect on leaf δ¹⁵N values of male and female plants. Leaf δ¹⁵N values of the female plants were lower than the male plants from 105 to 150 DAF (rapid accumulation stage of oil and citral contents). δ¹⁵N values showed double peaks during 105 and 165 DAF, and the largest values were appeared at 105 and 135 DAF. Meanwhile, δ¹⁵N value of the female plant was lowest at 120 DAF, while the lowest value was appeared in the male plant at 165 DAF. 3) The mean leaf carbon contents of the female and male plants were 49.44% and 49.28% respectively. Leaf carbon contents were higher in the female plant than in the male plant at 105 and 120 DAF, while lower in the female plant than in the male plant from 135 DAF to 165 DAF (from accumulation stage to stable stage of oil content). The leaf carbon contents significantly increased with time in the male plant, but not significantly in the female in different periods. 4) The mean leaf nitrogen contents of the female and male plants were 1.71% and 1.51%. Sex had a significant effect on the leaf nitrogen content, and the leaf nitrogen contents of the male plants were lower than the female plants from 105 to 165 DAF (except for 135 DAF). 5) The mean leaf C/N of the female and male plants was 29.15 and 33.72. Sex had a significant effect on C/N, and the female plants had a lower C/N than the male plants, regardless of time. The decreased value of C/N was higher in the male plants than in the male plants from 135 to 165 DAF. 6) There were no correlations between δ¹³C and the nitrogen content and between δ¹³C and δ¹⁵N.[Conclusion] The sexes of the L. cubeba differ in terms of temporal patterns of water use efficiency and nitrogen use. The water use efficiency of female plant was lower than that of male plant, and constantly declined from rapid accumulation stage to stable stage of oil and citral contents. The nitrogen use efficiency of female plant was also lower than that of male plant, and the nitrogen use efficiency of female and male plants showed double peaks. The nitrogen content of male plant was lower than that of female plant, allocating more nitrogen to flower buds for pollen formation. The carbon content of female plant was lower than that of male plant from the rapid accumulation stage to stable stage of oil and citral contents, supplying more carbon for fruit and seed formation.

Key words: dioecy, Litsea cubeba, water use efficiency, nitrogen use efficiency