Genetic variation for sensitivity to a thyme monoterpene in associated plant species

Department of Biological Sciences, University of Aarhus, Ny Munkegade, Build. 1540, 8000 Arhus C, Denmark.
Oecologia (Impact Factor: 3.09). 11/2010; 162(4):1017-25. DOI: 10.1007/s00442-009-1501-z
Source: PubMed


Recent studies have shown that plant allelochemicals can have profound effects on the performance of associated species, such that plants with a history of co-existence with "chemical neighbour" plants perform better in their presence compared to naïve plants. This has cast new light on the complexity of plant-plant interactions and plant communities and has led to debates on whether plant communities are more co-evolved than traditionally thought. In order to determine whether plants may indeed evolve in response to other plants' allelochemicals it is crucial to determine the presence of genetic variation for performance under the influence of specific allelochemicals and show that natural selection indeed operates on this variation. We studied the effect of the monoterpene carvacrol-a dominant compound in the essential oil of Thymus pulegioides-on three associated plant species originating from sites where thyme is either present or absent. We found the presence of genetic variation in both naïve and experienced populations for performance under the influence of the allelochemical but the response varied among naïve and experienced plant. Plants from experienced populations performed better than naïve plants on carvacrol soil and contained significantly more seed families with an adaptive response to carvacrol than naïve populations. This suggests that the presence of T. pulegioides can act as a selective agent on associated species, by favouring genotypes which perform best in the presence of its allelochemicals. The response to the thyme allelochemical varied from negative to neutral to positive among the species. The different responses within a species suggest that plant-plant interactions can evolve; this has implications for community dynamics and stability.

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    • "We assumed that the selective pressure of polyphenolic allelochemicals released by Myriophyllum spp. on P. duplex strains is important under the given environments (water bodies dominated by allelopathically-active macrophytes). Responses within one species were shown to vary as a result to the co-occurrence with allelochemicals in terrestrial environments [23]. Further, local genetic adaptation for grazing resistance traits in natural populations of the green alga D. armatus that were exposed to contrasting grazing pressures by zooplankton were detected [5], and a fast genetic adaptation of the green alga Dictyosphaerium chlorelloides to moderate acidic and metal rich waters was found [16]. "
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    • "Understanding the conditionality of allelopathy is important because a growing body of evidence indicates that allelochemicals contribute to the way plant species interact (Lankau and Strauss 2007; Jensen and Ehlers 2010; Barto et al. 2011). In particular, allelopathy has been implicated as a mechanism in a number of exotic plant invasions (Rice 1984; Callaway and Aschehoug 2000; Prati and Bossdorf 2004; Inderjit et al. 2011; Murrell et al. 2011). "
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    ABSTRACT: Background: Conditionality in the occurrence or strength of interactions among species yields insight into the relative importance of different ecological factors and provides a deeper understanding of the mechanisms through which organisms interact. Aims: We explored light-dependent conditionality of the allelopathic effects of Centaurea stoebe, an exotic invasive forb in North America, on Koeleria macrantha, a North American native bunchgrass. Methods: We compared the total biomass of K. macrantha competing with C. stoebe in high- and low-light treatments and in substrate with and without activated carbon. Results: Koeleria biomass did not differ in low- and high-light treatments when grown alone and was highly suppressed by C. stoebe in both low and high light; however, high-light activated carbon treatments designed to ameliorate root-mediated allelopathic effects resulted in an almost seven-fold increase in Koeleria mass in comparison to no carbon treatments. Activated carbon had significant but much weaker positive effects in low light. Activated carbon had no effect on Koeleria in the absence of C. stoebe. Conclusions: Other research shows that C. stoebe decreases sharply in abundance under tree canopies, and under canopies its typically strong competitive effects on natives in open grasslands are reduced. Our results provide a hypothesis for these patterns, suggest a possible mechanism for light-dependent conditionality in the way plants interact, and suggest that in vivo greenhouse experiments at moderate light levels may provide conservative evidence for allelopathy.
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