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Is differential use of Juniperus monosperma by small ruminants driven by terpenoid concentration?

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We examined the relationship between volatile plant secondary metabolite concentrations and Juniperus monosperma herbivory by small ruminants. Two groups of animals (10 goats or 5 goats plus 4 sheep) browsed 16 paddocks (20 x 30 m) containing one-seed juniper for six days during two seasons. Juniper leaves were sampled from 311 saplings on the same day they were browsed. Saplings were categorized by size (short [< 0.5 m], medium [0.5-1.0 m] or tall [> 1.0 m]) and browsing intensity (light [<33%], moderate [33-66%] or heavy [>66%]). Juniper bark was also collected from 12 saplings during spring. 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 a-pinene (11.1 ± 0.2 and 7.6 ± 0.7 mg/g, respectively). Total terpenoid concentration was greater in spring than summer (20.6 ± 0.5 vs. 16.7 ± 0.3 mg/g, respectively) and lower in short 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 among the three defoliation categories (16.1 ± 0.4, 18.7 ± 0.5, and 21.2 ± 0.6 mg/g for heavy, moderate, and light, respectively). The smallest subset of terpenes able to discriminate between heavy and light browsing intensity categories included eight compounds ([E]-ß-farnesene, bornyl acetate, y-eudesmol, endo-fenchyl acetate, y-cadinene, a-pinene, cis-piperitol, and cis-p-menth-2-en-1-ol). Our results suggest terpenoid concentrations in one-seed juniper are related to season, sapling size, and browsing by small ruminants.
R. E. Estell , S. A. Utsumi , A. F. Cibils , D. M. Anderson
Juniperus monosperma , bark , bornyl acetate , browsing , defoliation , farnesene , goats , herbivores , leaves , pastures , saplings , sheep , spring , summer
USDA Scientist Submission
Journal of chemical ecology 2014 v.40
Journal Articles, USDA Authors, Peer-Reviewed
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