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Abstract

Lavandula stoechas, a native plant of Greece, is rich in essential oil and fenchone is its major constituent. We examined the effect of the essential oil and its main constituents on soil metabolism and microbial growth. Addition of the essential oil or fenchone to soil samples induced a remarkable increase in soil respiration. This was accompanied by an increase in the soil bacterial population of three orders of magnitude. This sizable population was not qualitatively similar to that of the control soil samples. One bacterial strain dominated soil samples treated with L. stoechas essential oil or fenchone. By use of the disk diffusion assay, we evaluated the capacity of three bacterial strains that we isolated from the soil samples, as well as Escherichia coli and Bacillus subtilis (reference strains), to grow in the presence of the essential oil and three of its main constituents (fenchone, cineol, alpha-pinene). The substances tested did not inhibit the growth of the strain found to dominate the bacterial populations of treated soil samples; they severely inhibited B. subtilis. The other two isolated strains could also grow in liquid cultures in the presence of different quantities of essential oil or fenchone. Addition of fenchone at the end of the exponential phase increased the cell numbers of the strain that dominated the bacterial populations of treated soil samples, indicating use of the substrate added. On the basis of these results, we propose a scheme of successional stages during the decomposition process of the rich-in-essential-oil litter of aromatic plants that abound in the Mediterranean environment.

Instantaneous responses of microbial communities to stress in soils pretreated with Mentha spicata essential oil and/or inoculated with arbuscular mycorrhizal fungus

“…The number of asterisks corresponds to level of significance (*p < .05, **p < .01, ***p < .001) as this was demonstrated by analysis of variance (ANOVA), while their color corresponds to a specific effect (red: AMF, green: AC, blue: AMF + AC) F I G U R E 2 Percentage changes in the activity of different enzymes relative to control 3 days after stress exposure in three different treatments: only inoculated (arbuscular mycorrhizal fungus [AMF]), only acclimated (AC), jointly inoculated and acclimated samples (AMF + AC; joint). The number of asterisks corresponds to level of significance (*p < .05, **p < .01, ***p < .001) as this was demonstrated by analysis of variance (ANOVA), while their color corresponds to a specific effect (red: AMF, green: AC, blue: AMF + AC) the fact that essential oils are a readily decomposable carbon source to microorganisms (Vokou et al, 2002;Vokou & Margaris, 1988). Moreover, the quality of the decomposable material explained why there were no significant changes relative to the control in actinomycetes, which mineralize slowly relatively stable organic carbon substrates (Sharma, 2014).…”

“…Essential oils are constituents of aromatic plants that are common in the Mediterranean environment. The incorporation of essential oils or their major constituents into soils has stimulatory effects on bacterial populations (Vokou, Chalkos, Karamanlidou, & Yiangou, 2002), depresses specific fungal populations (Hassiotis & Dina, 2011;Kadoglidou et al, 2011) and can stimulate soil respiration (Vokou & Liotiri, 1999). Therefore, essential oils, by acting selectively on members of the community, may influence microbial community profiles (Lehmann et al, 2008).…”

Soil Microorganisms Alleviate the Allelochemical Effects of a Thyme Monoterpene on the Performance of an Associated Grass Species

“…These monoterpenes are known for their antimicrobial activity [8], [9], [10] mainly through their growth inhibitor effect on bacteria and fungi. However, it has been shown that some bacteria can decompose terpenes and use some of them as a carbon source [8], [9], [10]. One genus well known for its production of monoterpenes is Thymus .…”

Applying the Drosophila wing spot test to assess the genotoxic impact of 10 essential oil constituents used as flavouring agents or cosmetic ingredients

“…[21] Moreover, potential medical applications are ascribed to the monoterpenes S-(À)limonene, S-(+)-carvone, R-(À)-carvone and (À)-fenchone. [9,[22][23][24] Furthermore, all the tested monoterpenoids are main constituents of many common aromatic plants, such as Anethum graveolens L. (Apiaceae), [10,13,25] Carum carvi L. (Apiaceae), [10,13] Foeniculum vulgare Mill (Apiaceae), [26] Lavandula angustifolia Mill (Lamiaceae), [27] Lavandula stoechas L. (Lamiaceae), [27] Mentha spicata L. [8,28] and other Mentha species, [21] Ocimum basilicum L., [29] etc.…”