PARENT SESSION
Poster Session #4: Herbivory.
Monday, August 5. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Effects of long-term nitrogen and phosphorous fertilization on sarmentosin production by Yellow Stonecrop, Sedum lanceolatum.

Garrigan, Dana^*,1, ¹ Department of Biology, Tacoma, WA

ABSTRACT- Yellow stonecrop (Sedum lanceolatum) plants produce the cyanoglucoside sarmentosin for chemical defense. Previous investigations at our study site on Niwot Ridge in Colorado have demonstrated that sarmentosin is sequestered by the Small Apollo butterfly Parnassius phoebus. I have hypothesized that the increasing rates of nitrogen deposition recorded on Niwot Ridge may alter the nutrient availability to S. lanceolatum, and consequently affect its allocation of resources to growth versus chemical defense. Since sarmentosin is a nitrogen-containing defensive compound, nitrogen enrichment might be expected to result in greater production of sarmentosin by stonecrops, potentially altering their interaction with feeding P. phoebus larvae. To examine the effects of nitrogen enrichment on production of sarmentosin by S. lanceolatum, sarmentosin and nitrogen contents of plants from long-term fertilization plots were measured. Over the previous decade, plants had received one of four treatments – annual fertilization with nitrogen, phosphorous, both nitrogen and phosphorous, or no fertilization. Stonecrops receiving nitrogen fertilization produced significantly more sarmentosin than plants in control plots or plots that were fertilized with phosphorous alone. Interestingly, plants receiving fertilization with both nitrogen and phosphorous produced less sarmentosin than plants that had been fertilized with nitrogen alone. This result is consistent with the predictions of the nutrient balance hypothesis for plant defense allocations. Overall, there was a significant correlation between the mean nitrogen concentration of plants in each treatment and the mean concentration of sarmentosin (r²=0.96).

KEY WORDS: sedum lanceolatum, plant chemical defense, nitrogen deposition, Niwot Ridge