Relationship between one-seed juniper terpene concentration and herbivory by small ruminants

TitleRelationship between one-seed juniper terpene concentration and herbivory by small ruminants
Publication TypeConference Proceedings
Year of Publication2013
AuthorsEstell RE, Utsumi S.A, Cibils AF, Anderson D.M.
Conference NameADSA-ASAS Joint Annual Meeting
Date Published07/2013
PublisherJournal of Animal Science
Conference LocationIndianapolis, IN
ARIS Log Number296543
Keywordsgoat, sheep, terpene

Plant secondary metabolite affect the amount of use by herbivores for serveral woody species.  We examined the relationship between terpenoid concentrations and Juniperus monosperma herbivory by small ruminants.  The study was part of a larger effort in which goats (n = 10) or mixed species (5 goats and 4 sheep) were allotted to 16 plots (20 × 30 m) containing one-seed juniper for 6 d during 2 seasons at 2 stocking rates. Juniper leaves were sampled from 311 saplings on the same day they were browsed. Saplings were categorized by size (small [<0.5 m], medium [0.5-1.0 m] or tall [>1.0 m]) and browsing intensity (low [<33%], moderate [33-66%] or heavy [>66%] herbivory). Juniper bark was also collected from 12 saplings during spring. Leaves and bark were analyzed for terpenoids with gas chromatography-mass spectrometry. Terpene data were pooled across species and stocking rate and ANOVA was conducted for season, sapling size, and herbivory level. The volatile profile of one-seed juniper leaves and bark consisted of 65 and 55 compounds, respectively. Total estimated terpenoid concentrations in leaves and bark were 18.3 ± 0.3 and 8.9 ± 0.8 mg/g, respectively, and the dominant terpene in both tissues was α-pinene (11.1 ± 0.2 and 7.6 ± 0.7 mg/g, respectively). Total terpenoid concentration was greater (P < 0.001) in spring than summer (20.6 ± 0.5 vs. 16.7 ± 0.3 mg/g, respectively) and lower (P < 0.001) in small saplings than medium or tall saplings (16.5 ± 0.6 vs. 19.8 ± 0.4 and 19.5 ± 0.4 mg/g, respectively). Total concentration also differed (P < 0.001) among all 3 browsing categories (16.1 ± 0.4, 18.7 ± 0.5, and 21.2 ± 0.6 mg/g for heavy, moderate, and light herbivory, respectively). Approximately 42% of the variation in browsing intensity could be explained (P < 0.001) by 12 compounds ([E]-β-farnesene, cis-sabinene hydrate, bornyl acetate, γ-eudesmol, germacrene A, γ-cadinene, α-pinene, [Z]-β-ocimene, terpin-4-ol, cispiperitol, cis-p-menth-2-en-1-ol, and camphene hydrate). Our results indicate that the terpene profile of one-seed juniper is related to sapling size, season, and degree of use by sheep and goats.