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Abstract:
Solidago altissima is a dominant perennial of old field succession in North America with the ability to form dense, almost monospecific stands; the plant is also considered an aggressive invasive throughout Europe and Japan. S. altissima’s success is facilitated by large belowground rhizome systems that allow clonal spread and possible allelopathic suppression of competitors. A diversity of polar and nonpolar terpenes and polyacetylenes have been described from S. altissima rhizomes; however, there is little information documenting the concentration or distribution of these allelochemicals and how they relate to plant defense hypotheses. We thus developed a GC–MS method to simultaneously quantify rhizome terpenes and polyacetylenes that spanned a range of polarities and confirmed the presence of 19 terpenoids in addition to the polyacetylene dehydromatricaria ester (DME). We, (1) determined relative concentrations and variability of mono-, sesqui-, neutral diterpenes, diterpene acids and DME within a central NY population; (2) compared accumulation of these compounds in differently developed rhizome tissue; and (3) tested the alleopathic effect of DME at naturally occurring concentrations on germination and seedling growth of Asclepias syriaca, a common competitor of S. altissima. Overall, diterpene acids dominated the phytochemical profile of most genotypes (averaging 0.75% of fresh mass) with kolavenic acid being the single most abundant component. Monoterpene, sesquiterpene and acidic diterpene concentrations were all significantly greater in the actively elongating (current-year) rhizomes compared to established rhizomes and followed optimal defense theory predictions. Conversely, DME levels were lower in the current-year rhizomes than in established rhizomes. DME inhibited seed germination of A. syriaca in a dose-dependent manner. The tissue-specific accumulation of the different compounds may represent a biosynthetic and/or allocational strategy that limits the exposure of young-tissue to high concentrations of DME possibly limiting the cytotoxic effects of DME.
