Essential Oil Yield and Composition Reflect Browsing Damage of Junipers

Abstract

The impact of browsing on vegetation depends on the relative density and species composition of browsers. Herbivore density and plant damage can be either site-specific or change seasonally and spatially. For juniper (Juniperus communis) forests of a sand dune region in Hungary, it has been assumed that plant damage investigated at different temporal and spatial scales would reflect selective herbivory. The level of juniper damage was tested for a possible correlation with the concentration of plant secondary metabolites (PSMs) in plants and seasonal changes in browsing pressure. Heavily browsed and nonbrowsed junipers were also assumed to differ in their chemical composition, and the spatial distribution of browsing damage within each forest was analyzed to reveal the main browser. Long-term differences in local browsing pressure were also expected and would be reflected in site-specific age distributions of distant juniper populations. The concentrations of PSMs (essential oils) varied significantly among junipers and seasons. Heavily browsed shrubs contained the lowest oil yield; essential oils were highest in shrubs bearing no damage, indicating that PSMs might contribute to reduce browsing in undamaged shrubs. There was a seasonal fluctuation in the yield of essential oil that was lower in the summer period than in other seasons. Gas chromatography (GC) revealed differences in some essential oil components, suggesting that certain chemicals could have contributed to reduced consumption. The consequential long-term changes were reflected in differences in age distribution between distant juniper forests. These results confirm that both the concentration of PSMs and specific compounds of the essential oil may play a role in selective browsing damage by local herbivores.

Both Gas Chromatography and an Electronic Nose Reflect Chemical Polymorphism of Juniper Shrubs Browsed or Avoided by Sheep

“…The browsed groups were well demarcated from the non-browsed groups, but some browsed shrubs (ID: 2, 5, 6) showed nonbrowsed odor characteristics in both classification methods is the first study to identify uncommonly high amount of this monoterpene in J. communis. The observed juniper population was rich in monoterpenes (Markó et al, 2008) similarly to other stands of this species (e.g., Butkiene et al, 2004). The factor analysis of the essential oil pattern determined by GC resulted in three factors: F1 contained monoterpenes with medium retention times; F2 contained sesquiterpenes; whereas F3 was related to dominant monoterpenes.…”

“…Heavily browsed (N=9) and non-browsed (N=9) shrubs of J. communis were chosen, and all plant material was collected at late winter. The sampling procedure was detailed in Markó et al (2008). The size (height 2-2.5 m) and sex (female) of the sampled shrubs were similar, reducing the possible impact of these factors.…”

“…Moreover, these components may produce either synergistic or antagonistic interactions with each other (Aparicio et al, 1996;Vokou et al, 2003) influencing the toxicity of the whole mixture. Furthermore, essential oil content shows high diversity with habitat and season (Riddle et al, 1996;Vourc'h et al, 2001;Gomez et al, 2003;Markó et al, 2008) and is also variable among individuals of a particular species (Miller et al, 2005).…”

“…Recently, Markó et al (2008) found that both the concentration of PSMs and specific compounds of the essential oil may play a role in selective browsing damage. The main goal of this study was the characterization of the volatile chemical composition of the common juniper, Juniperus communis L., either browsed or non-browsed by sheep.…”

Essential oils of indigenous in Greece six Juniperus taxa

“…The specimen J. communis sensu lato has attracted significant research interest, mainly because of its edible fruits which produce a thoroughly investigated EO (Chatzopoulou et al 2002;Milojevic et al 2008;Orav et al 2010aOrav et al , 2010b. The EO derived from its leaves was also studied (Orav et al 2010a(Orav et al , 2010b providing interesting data in respect the plant's chemodiversity (Filipowicz et al 2009) and the relation between stress and composition (Marko et al 2008). The EO derived from the leaves of J. communis L. ssp.…”