While allelopathy has been documented in laboratory settings, its importance in controlling plant community dynamics has been much more difficult to assess. Goldenrod species are often found to be allelopathic and are important components of successional systems. Therefore we conducted laboratory bioassays for six goldenrod species and compared these results to their influences on other species in the field. Field data came from the Buell-Small Succession Study (BSS), a long-term study of vegetation dynamics in abandoned agricultural land. Leaves of six goldenrods: Solidago nemoralis, S. gigantea, S. canadensis, S. juncea, S. rugosa, and Euthamia graminifolia were collected from the BSS site. We determined the germination responses of two target species (radish and lettuce) to a gradient of leaf extract concentrations to assess allelopathic potential. We paired this data with the influence of each goldenrod species on the species richness and community turnover in the BSS permanent plots.
Results/Conclusions
Most goldenrod species were found to be allelopathic to some degree as germination percentages were reduced by leaf extracts. There was also variation between assay species (lettuce and radish) in which goldenrod species was the most allelopathic. However, the field data did not correlate with the bioassay data. Influences of goldenrods on their associated communities were weak in general. Those goldenrod species which exhibited effects were often positively associated with local species richness. Similarly, influences on species turnover were only significant in one species, S. juncea, which increased local colonization rates. In this system, we documented the potential for goldenrods to exhibit allelopathic interactions, but these effects were not strong enough to alter community structure or dynamics. In fact, goldenrods seem to facilitate, rather than inhibit associated plant species. Although most studies of allelopathy are conducted in the lab, these studies must be paired with field data to assess the importance of allelopathy in determining plant community dynamics.