Submitted to: Biochemical Systematics and Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2012
Publication Date: 1/15/2013
Publication URL: http://handle.nal.usda.gov/10113/57175
Citation: Estell, R.E., James, D.K., Fredrickson, E.L., Anderson, D.M. 2013. Within-plant distribution of volatile compounds on the leaf surface of Flourensia cernua. Biochemical Systematics and Ecology. 48:144-150.
Interpretive Summary: Shrub expansion into arid grasslands is of concern to livestock producers and ecologists. Many shrubs contain chemicals that make them unpalatable to livestock and wildlife. We have been studying how one class of compounds (terpenes) affects the use of tarbush by livestock. In this study, we examined the within-plant distribution of these chemicals in order to minimize sample variability and increase sampling efficiency. Of the 94 compounds measured on the leaf surface, 52 differed because of leaf position and 63 differed due to leaf age. Most of the sample variation could be eliminated by avoiding basal leaves and immature leaves.
Technical Abstract: We are using Flourensia cernua as a shrub model to study the role of terpenes on intake by livestock. Two experiments were conducted to examine distribution of volatile chemicals within a plant in an effort to minimize sample variability. In Exp. 1, leaves (current year's growth) were collected from 20 tarbush plants. Two leaders were sampled from each of three positions (outer canopy, subcanopy, and basal) in all four quadrants (based on ordinal direction). In Exp. 2, 10 leaders of current year's growth were removed from another 20 plants. Leaders were collected from the outer canopy of each quadrant and separated into thirds before removing leaves, thereby creating three leaf age categories. Volatile compounds were extracted with ethanol and analyzed with gas chromatography/mass spectrometry. Ninety-four chemicals (including 15 unknowns) were present on the leaf surface of F. cernua. Although 14 and 21 compounds differed (P < 0.05) among quadrants in Exp. 1 and 2, respectively, no consistent quadrant effect was detected in either study. Leaf position differed (P < 0.05) for 52 chemicals in Exp. 1 but outer canopy and subcanopy leaves differed for only 10 compounds. In Exp. 2, 63 compounds differed among leaf age categories. Immature leaves contained greater concentrations of 46 chemicals (P < 0.05) than moderate or mature age categories, but moderate and mature leaves differed for only seven compounds. Estimated total concentration (i.e., cumulative concentration of all compounds) was not affected by leaf position but varied among leaf age categories (P < 0.05; immature > moderate > mature). Differences in leaf position were attributed about equally to mono- and sesquiterpenes, whereas leaf age was affected to a greater extent by sesquiterpenes. Leaf position and maturity both affect terpene concentration and sampling variability for tarbush. However, little difference was detected between subcanopy and canopy positions. Thus, by avoiding basal sprouts and sampling from the mid-point of current year's growth, sampling variation should be minimal.