Influence of Plant Material Handling Protocols on Terpenoid Profiles of One-Seed Juniper Saplings

Abstract

Accurate estimation of one-seed juniper (Juniperus monosperma [Engelm.] Sarg.) intake by herbivores 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 leaves from 10 short (0.5 m +/- 0.05, mean +/- SE) and 10 tall (1.14 m +/- 0.06) one-seed juniper saplings subjected to 3 handling protocols: a) placed on dry ice after clipping and stored after 5 hours at –80 degreesC for 3 weeks (Control); b) kept at ambient temperature for the first 24 hours and then frozen at –80 degreesC for 3 weeks; or c) kept at ambient temperature for the first 24 hours, and then stored at 8 degreesC for 3 weeks. Juniper saplings contained 51 terpenoids, 3 of which were unknown compounds. Fourteen terpenoids accounted for 95% of the total amount of volatiles. The most abundant compound was a-pinene, which accounted for 65% of total terpenoids present. Handling protocols were not associated with detectable differences in total terpenoid content (Means +/- SE, Control: 21.68 +/- 1.42 mg g-1 dry matter [DM]; Frozen after 24 hours: 19.55 +/- 1.08 mg g-1 DM; Refrigerated after 24 hours: 18.80 +/- 1.13 mg g-1 DM). However, total terpenoid amount and concentration of a few major compounds tended to decrease with increasing storage temperature. Handling protocols induced detectable variations in a small number of minor terpenoids. We observed large among-plant variation in terpenoid profiles that was not fully explained on the basis of sapling size. This study suggests that the length of storage period of one-seed juniper branches should not exceed 3 weeks and that storage refrigeration temperatures should be kept below 8 degreesC to prevent significant alterations in terpenoid profiles.