Intra- and intergenotype variation in Solidago altissima (Asteraceae) rhizome terpenoids, and the polyacetylene dehydromatricaria ester

Background/Question/Methods   Solidago altissima is a dominant perennial of old field succession in northern and central North America with the ability to form dense, almost monospecific stands; the plant is also considered an aggressive invasive throughout Europe and Japan.  The success of S. altissima is aided by large below-ground rhizome systems that allow clonal spread and possible allelopathic suppression of competitors.  A number of phytochemicals have been described from S. altissima rhizomes including diverse terpenoids and the allelopathic polyacetylene dehydromatricaria ester (DME).  There is little information documenting either the concentration or distribution of S. altissima rhizome allelochemicals within or between genotypes nor the ecological function of these allelochemicals in native habitats.  To better understand this system, we developed a GC/MS method to simultaneously quantify rhizome monoterpenes, sesquiterpenes, acidic and nonacidic diterpenes and polyaceletylenes.  We sought to: (1) determine overall mean concentrations and variability of each chemical class within a central NY population; (2) compare mean concentrations and variability between actively elongating (current year) and established (> 1 yr) rhizomes; (3) identify possible herbivores damaging S. altissima rhizomes in the field and determine modes of feeding and incidence of  attack.

Results/Conclusions   Twelve terpenoids in addition to DME were identified with each phytochemical class exhibiting a high degree of variability.  Nonetheless, diterpene acids dominated the phytochemical profile of most genotypes (averaging 0.75% of fresh mass) with kolavenic acid being the single greatest component.  Monoterpene, sesquiterpene and acidic diterpene concentrations were all significantly greater (P< .001) in the elongating rhizomes compared to established rhizomes.  Terpene differences between elongating and established rhizomes are in general agreement with Optimal Defense Theory which predicts increased defense of high-value tissues.  Approximately 26% of the established rhizomes (> 1 yr) processed for chemical analysis exhibited damage by cortex mining Eucosma sp. (Tortricidae) larvae; however, little herbivore damage to the softer elongating rhizomes was observed.  Conversely, mean DME level (± 1SE) of the elongating rhizomes (69.0 ± 46.3 μg g^-1 fresh mass) was lower (P< .001) than that of the established rhizomes (370.4 ± 85.6).  Furthermore, approximately half of the elongating samples exhibited no detectable DME.  Because DME is cytotoxic and known to inhibit radicle growth in other species, the low levels of DME but high levels of terpenoid chemicals in the actively elongating rhizomes may result from a biosynthetic or allocational strategy to limit DME autotoxicity to meristematic tissue.