Soil nitrogen availability and herbivore attack influence the chemical defenses of an invasive plant (Linaria dalmatica; Plantaginaceae) |
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Authors: | Mary A Jamieson M Deane Bowers |
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Institution: | (1) Department of Ecology and Evolutionary Biology, University of Colorado, UCB 334, Boulder, CO 80309, USA;(2) Museum of Natural History and Department of Ecology and Evolutionary Biology, University of Colorado, UCB 334, Boulder, CO 80309, USA;(3) Colorado State University, 1177 Campus Delivery, Fort Collins, CO 80523, USA |
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Abstract: | Chemical defenses are thought to contribute to the invasion success and impacts of many introduced plants; however, for most
of these species, little is known about these compounds and how they vary in natural environments. Plant allelochemical concentrations
may be affected by a variety of abiotic and biotic factors, including soil nutrients and herbivores. Moreover, such quantitative
variation is likely to play an important role in species interactions involving these invasive plants. The purpose of this
study was to examine patterns of variation in iridoid glycoside concentrations of the invasive plant Linaria dalmatica (Plantaginaceae). We conducted a greenhouse experiment to investigate the effect of soil nitrogen availability on iridoid
glycoside concentrations. Results from this experiment showed that plant iridoid glycoside concentrations decreased with increased
nitrogen availability. Additionally, plants were collected from multiple field sites in order to characterize the influence
of population, soil nitrogen availability, and herbivore attack on iridoid glycoside variation. Results from field studies
indicated that plants demonstrated considerable seasonal variation, as well as variation within and among populations, with
iridoid glycoside concentrations ranging from approximately 1 to 15% dry weight. The relationship between soil nitrogen and
plant iridoid glycosides varied among populations, with a strong negative correlation in one population, a marginally significant
negative relationship in a second population, and no relationship in the remaining two populations. Additionally, we found
a negative relationship between iridoid glycoside concentrations and plant injury by an introduced biocontrol agent, the stem-mining
weevil Mecinus janthinus (Cucurlionidae). These results show that plant allelochemical concentrations can vary widely in natural environments and
suggest that levels of plant defense may be reduced by increased soil nitrogen availability and herbivore attack in this invasive
plant species. |
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