Soil nitrogen availability and herbivore attack influence the chemical defenses of an invasive plant (Linaria dalmatica; Plantaginaceae)

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.

Nitrogen enrichment differentially affects above‐ and belowground plant defense

“…However, four to fi ve resource levels are recommended for adequately testing predictions of the growth differentiation balance hypothesis ( Stamp, 2003, and references therein). Moreover, results presented here are in contrast to those of a previous greenhouse experiment, which showed a negative relationship between nitrogen availability and iridoid glycoside concentrations of L. dalmatica growing under four N levels, ranging from zero to 8 g/m 2 ( Jamieson and Bowers, 2012b ), but those results did not fully support predictions of the Fig. 1.…”

Light and Nutrient Dependent Responses in Secondary Metabolites of Plantago lanceolata Offspring Are Due to Phenotypic Plasticity in Experimental Grasslands

“…There is ample evidence that environmental parameters such as light, nutrients, ozone, CO 2 , water availability and temperature strongly affect the concentration of these defense compounds in plant tissues [ 1 – 4 ]. Nitrogen limitation for example can enhance the concentration of phenolic compounds [ 5 , 6 ] and other carbon based metabolites such as iridoid glycosides [ 7 , 8 ] and thus may have beneficial effects on plant defense against antagonists. Light availability also strongly affects the production of secondary metabolites such as terpenes and phenolics [ 9 , 10 ].…”

Plant‐mediated effects of soil nitrogen enrichment on a chemically defended specialist herbivore,Calophasia lunula

“…In these experiments, L. dalmatica plants demonstrated lower levels of iridoid glycosides as well as less variation compared with plants from field populations (Jamieson & Bowers, 2010, 2012. In these experiments, L. dalmatica plants demonstrated lower levels of iridoid glycosides as well as less variation compared with plants from field populations (Jamieson & Bowers, 2010, 2012.…”

“…In this study, we found no effect of a six-fold increase in nitrogen availability (2-12 g m −2 ) on L. dalmatica iridoid glycoside concentrations. However, in a previous study (Jamieson & Bowers, 2012), there was an approximate 30% decrease in iridoid glycoside concentrations when soil nitrogen was increased from 2 to 8 g m −2 . In that study, nitrogen treatments were applied over 5 weeks compared with 10 weeks in this study.…”

“…Calophasia lunula is a specialist herbivore of Linaria spp. Except in the case of Jamieson and Bowers (2012), these previous studies focused on nutrient enrichment [using either a complete nutrient or nitrogen:phosphorous:potassium (N : P : K) addition] and thus did not isolate the effects of increased nitrogen. Several previous studies involving other iridoid glycoside producing plants, such as Plantago spp., have demonstrated a decrease in plant iridoid glycoside concentrations with increased nutrient availability (Fajer et al, 1992;Darrow & Bowers, 1999;Jarzomski et al, 2000;Marak et al, 2003;Prudic et al, 2005;Jamieson & Bowers, 2012).…”