|Estell, Richard - Rick|
Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2006
Publication Date: 11/1/2006
Citation: Utsumi, S.A., Cibils, A.F., Estell, R.E., Wang, Y.F. 2006. Influence of plant material handling protocols on terpenoid profiles of one-seed juniper saplings. Rangeland Ecology and Management. 59:668-673. Interpretive Summary: One-seed juniper invasion into previously cleared woodlands is a concern to range managers throughout the southwestern United States. Browsing with sheep and goats could be a tool for juniper control, and success may depend on improving the animal's ability to detoxify plant terpenoids in order to promote levels of herbivory that might suppress juniper growth and recruitment. In order to test effects of various treatments on juniper intake, we first need to understand the effects of harvesting, transporting, and storing plant material to be used in pen experiments. Such manipulation may change the concentration of volatile compounds such as terpenes, and therefore affect herbivory levels. We analyzed the terpene profiles of leaves from small and large one-seed juniper saplings subjected to different handling protocols (immediate freezing vs. freezing after 24 hours, and freezing vs. refrigerating after 24 hours). Juniper saplings contained a mixture of 51 terpenoids, three of which were unknown compounds. Alpha-pinene was the most abundant compound, accounting for 65% of the total terpenoid concentration. Total terpenoid content did not differ among handling protocols. Handling protocols appeared to induce only slight variations in a few minor terpenoids. However, large plant-to-plant variation in terpenoid profiles that was not related to plant size was observed. This study suggests that juniper feeding trials can be simplified using plant material refrigerated for three weeks without significant change in terpenoid profiles, but among-plant variation in chemical composition must be considered in pen feeding trials.
Technical Abstract: Accurate estimation of one-seed juniper (Juniperus monosperma (Englem). Sarg.) intake by goats and sheep often requires harvesting, transporting, and storing plant material that is later used in pen experiments. Such manipulation could alter terpenoid profiles and modify herbivory levels significantly. We used gas chromatography mass spectrometry (GC/MS) to analyze the terpenoid profile of the ethanol extract of leaves of small and large one-seed juniper saplings subjected to three different handling protocols. Plant materials were either: a) placed on dry ice after clipping and then at -80º C until analysis (Control); b) stored at ambient temperature during the first 24 hours and then frozen; or c) stored at ambient temperature during the first 24 hours, and then stored at 8ºC for 3 weeks. Juniper saplings contained a mixture of 51 terpenoids, three of which were unknown compounds. Only 14 terpenoids accounted for 95% of the total volatiles extracted. Alpha-pinene was the most abundant compound, accounting for 65% of total terpenoid concentration. Total terpenoid content did not differ among handling protocol treatments (Control: 21,682.19 ±1,424.72 'g g-1 DM; Frozen after 24 h: 19,553.63 ±1,081.88 'g g-1 DM; Refrigerated for three weeks: 18,799.89 ±1,126.03 'g g-1 DM). Handling protocols appeared to induce only slight variations in a small number of minor terpenes. We detected large among-plant variation in terpenoid profiles that was not fully explained by sapling size. This study suggests that juniper feeding trials can be simplified using plant material stored at 8ºC for three weeks without significant alteration of terpenoid profiles. Among-plant variation in chemical composition, however, must be considered in pen feeding trials.