Within-plant distribution of volatile compounds on the leaf surface of Flourensia cernua

We are using Flourensia cernua as a shrub model to study how terpenes affect livestock herbivory. Two experiments were conducted to examine distribution of volatile chemicals within a plant in an effort to minimize sample variability. In Experiment 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 Experiment 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 15unknowns)were presenton the leaf surface of F. cernua. Although 14 and 21 compounds differed (P < 0.05) among quadrants in Experiments 1 and2, respectively, no consistent quadrant effectwas detected in either study. Leaf position differed (P < 0.05) for 52 chemicals in Experiment 1 but outer canopy and subcanopy leaves differed for only 10 compounds. In Experiment 2, 63 compounds differed among leaf age categories. Immature leaves contained greater concentrations of 46 chemicals (P < 0.05) than intermediate or mature age categories, but intermediate 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 > intermediate >mature). Differences in leaf position were attributed about equally to monoand sesquiterpenes, whereas leaf age differences were primarily due to sesquiterpenes. Leaf position and age both affect terpene concentration and sampling variability for tarbush. However, little differencewas 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. Published by Elsevier Ltd.