Shifting scents: Analyzing the potential for phenotypic plasticity in floral odor production
Studies have shown that floral scent is essential for the reproductive success of many flowering plant species. Its presence, including aspects of emission rate and overall composition, can influence specific pollinator behavior. In turn, pollinator behavior can influence pollen export, fruit production, and seed set. Few studies, however, have shown whether floral scent is impacted by phenotypic plasticity, specifically in response to abiotic environmental factors. Nitrogen levels in the soil may have a particularly meaningful plastic effect on floral volatiles. Amino acids are produced from nitrates and ammonium compounds; both benzenoid and phenylpropanoid volatile compounds are derived from one particular amino acid, phenylalanine, in the shikimic acid pathway. Therefore, we hypothesized that Petunia hybridacultivars grown in soil with a higher nitrogen concentration would synthesize more benzenoid volatiles relative to the same cultivars grown in lower nitrogen concentrations; non-benzenoid volatiles would be synthesized in similar quantities regardless of nitrogen concentration, as amino acids are not used to produce these scent compounds. Floral scent emissions were collected using dynamic headspace extraction, and the samples were analyzed using GC-MS. All scent collection and chemical analyses were conducted independently by an undergraduate student. The faculty member and student worked collaboratively to complete analysis of all data.
We found that significantly more benzenoid volatiles were produced by Petunia hybrida grown in higher nitrogen concentrations than plants of the same cultivars grown in low nitrogen conditions, which is indicative of a plastic response. In contrast, the amount of non-benzenoid volatiles did not differ significantly across the two treatments, further supporting our hypotheses. If the emission rate of benzenoid volatiles serves as a cue for pollinators, such plasticity would greatly affect rates of pollination in environments with different nutrient levels in the soil. Subsequently, this would alter plant reproductive success in directions not predicted by traditional studies of plant-pollinator interactions. Thus, understanding the potential for phenotypic plasticity in floral scent could influence future ecological studies on Petunia hybrida and other angiosperms.