Year-round Variations in Essential Oil Content and Composition of Male and Female Juniper

Rocky Mountain juniper (Juniperus scopulorum Sarg.) is an evergreen dioecious tree (produces male and female plants). The pleasant aroma and the medicinal value of this species are the result of the essential oil. The hypothesis of this study was that the essential oil content and composition may be different in male and in female trees and also may be affected with seasonal changes throughout the year. The objective was to evaluate yearround variations in essential oil composition of Rocky Mountain juniper within single male and female trees. The concentration of essential oil in fresh leaves varied from 0.335% to 0.799%, and at most sampling points, the oil content in the biomass of the male tree was greater than that in the biomass of the female tree. There was a trend toward increased essential oil content in male juniper in 220 to 342 days after the first sampling (DAFS), compared with the one in 35 to 184 DAFS. The concentrations of the oil constituents alphapinene, alpha-terpinene, gamma-terpinene, terpinolene, pregeijerene B, elemol, betaeudesmol/alpha-eudesmol, and 8-alpha-acetoxyelemol were greater in the oil of the female tree than in the oil of the male tree. Conversely, the concentrations of alpha thujene, sabinene, myrcene, limonene, and delta-cadinene were greater in the oil of the male tree than in the oil of the female tree. However, the concentration gradient trends for both female and male trees were similar for myrcene and sabinene, for alpha-terpinene and terpinolene, for pereijerene B and elemol, and for beta-eudesmol/alpha-eudesmol and 8-alpha-acetoxyelemol. Overall, lower concentrations in the oils at 101 to 132 or 163 DAFS were found for myrcene and alpha-pinene sabinene, whereas the concentrations of gamma-terpinene, elemol (female tree), beta-eudesmol/alpha-eudesmol (female tree), and 8alpha-acetoxyelemol (female tree) were greater during this period. This study demonstrated that the content and composition of the essential oil from Rocky Mountain juniper are subject to seasonal changes and also depend on the sex of the tree. Rocky Mountain juniper (Juniperus scopulorum Sarg.), an evergreen dioecious gymnosperm, is a widespread species in the western United States (Arizona, Colorado, Idaho, Montana, North Dakota, Nebraska, New Mexico, Nevada, Oklahoma, Oregon, South Dakota, Texas, Utah, Washington, and Wyoming) and is found in Canada and in Mexico (Adams, 2004; Scher, 2002; USDA, 2011). Despite the wide ecological adaption, Rocky Mountain juniper is not a primary source for lumber because of relatively slow growth. However, Rocky Mountain juniper wood is highly valued for its durability, rich color, pleasant aroma, antioxidant activity, and is extensively used for interior paneling, furniture, various novelties, and fence posts. The species has been used extensively in the ethnobotany of native people of North America to treat a number of medical conditions. Native people of North America have been using the leaves as medicine and the wood for preparation of bows, lances, flutes, and other important items (Hart, 1976; Kroeber, 1908). Rocky Mountain juniper is also an important species in the arid and semiarid regions of North America for a number of wildlife species such as deer, elk, small mammals, and birds, which use it for cover and a food source (Rumble and Gobeille, 2013; Scher, 2002). These animals play a major role in seed dispersal. Rocky Mountain juniper leaves contain a significant amount of strongly aromatic essential oil, which has been subject to some previous studies (Adams and Hagerman, 1977; Adams and Powell, 1976; Cantrell et al., 2013; Zheljazkov et al., 2012a, 2012b). Previous investigations have found that sexual differences (Adams and Powell, 1976), seasonal changes (Powell and Adams, 1973), diurnal variations (Adams, 1979), and duration of distillation time (Zheljazkov et al., 2012a, 2012b) can affect Rocky Mountain juniper essential oil composition. However, there are no reports on variations of Rocky Mountain juniper essential oil yearround, from within a single tree, and on whether there are any seasonal differences between the composition of essential oil obtained from male and female trees grown side by side. Therefore, the objective of this study was to evaluate year-round variations in essential oil composition of Rocky Mountain juniper within one male and one female trees. Materials and Methods Plant material and essential oil steam distillation. All samples used in this study were generated from two adjacent large Rocky Mountain junipers (tree #470 male and tree #471 female) situated at the University of Wyoming Sheridan Research and Extension Center (ShREC) (lat. 44 50.373# N, long. 106 50.396# W, elevation 1140 m above sea level). Both trees were planted as part of a windbreak project at ShREC initiated by the U.S. Department of Agriculture in 1915 to 1917. Samples from the two trees were identified as specimens of Rocky Mountain juniper by Ms. Bonnie Heidel, botanist at the Wyoming Natural Diversity Database. All samples for distillation were generated in early morning ( 0800 HR) and distilled fresh. Sample size for each distillation was 500 g of fresh material in all three replicates. Rocky Mountain junipers (both male and the female trees) were sampled each month starting 12 Apr. 2011 and finishing on 19 Mar. 2012; there were 12 sampling points at the following DAFS: 1, 35, 62, 80, 101, 132, 163, 184, 220, 246, 286, 314, and 342. These DAFS correspond to 12 Apr. 2011, 17 May 2011, 13 June 2011, 1 July 2011, 22 July 2011, 22 Aug. 2011, 22 Sept. 2011, 13 Oct. 2011, 18 Nov. 2011, 14 Dec. 2011, 23 Jan. 2012, 20 Feb. 2012, and 19 Mar. 2012, respectively. The steam distillations were conducted as described previously (Zheljazkov et al., 2012a). Briefly, 500 g of fresh samples (collected at different heights and from different sides of the tree) were chopped into 2.5-cm pieces and immediately distilled in 2-L steam Received for publication 30 Apr. 2013. Accepted for publication 29 May 2013. This research was funded by the University of Wyoming startup funding and the Department of Plant Science allocation awarded to Dr. V. Zheljazkov. We thank Mrs. Adrienne Tatman, Mrs. Burnnie Foulke, Ms. Berva Brock, and Mrs. Leanne Roadifer for their help with the harvesting of the biomass and the extraction of the essential oil in the laboratory. We thank Dr. Mason MacDonald of Dalhousie University and Mrs. Rochelle Koltiska of the University of Wyoming for proof reading the manuscript internally and offering many suggestions. To whom reprint requests should be addressed; e-mail vjeliazk@uwyo.edu, Valtcho.pubs@gmail. com. HORTSCIENCE VOL. 48(7) JULY 2013 883 | POSTHARVEST BIOLOGY AND TECHNOLOGY