PARENT SESSION
Poster Session # 15: Plant Ecology.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Effects of nitrogen supplementation on growth, reproductions, and secondary chemistry of Solanum carolinense L.

Cipollini, Martin^*,, Paulk, Eric, Mink, Kim, Fischer, Tiffanny, Vaughn, Karen,

ABSTRACT- The effect of variation in nutrient and water availability on growth, reproduction, and fruit chemistry of Solanum carolinense L. was examined by focusing on three questions: 1) How does variation in N availability affect growth, reproductive output, and fruit pulp nutrient and secondary metabolite chemistry? 2) Is N supplementation correlated with increases in N-containing metabolites and decreases in C-based compounds, as predicted by the non-adaptive Carbon-Nutrient Balance hypothesis? 3) Do correlations exist between leaf and fruit chemical content, as suggested by the non-adaptive Physiological Constraints hypothesis? To address these questions, clones of 10 maternal plants were grown for three years (1998-2000) under two N treatments and two water treatments. At the end of each year, aboveground plant mass, fruit number, and fruit mass was determined. For each plant in 1999, we assayed ripe fruit pulp and leaf material for protein, sugar, phenolic, and glycoalkaloid content. We also analyzed a subset of ripe fruits for total glycoalkaloid content in 1998. While path analysis revealed strong direct and indirect effects of N treatment on growth and reproduction, fruit morphological and chemical variables were not strongly affected by N treatment. Fruit pulp chemistry remained rather constant despite the large differences in growth and reproduction that were associated with N variation. Leaf and ripe fruit chemical contents were not significantly correlated across treatments and maternal plants, and variation in leaf chemistry did not help explain variation in fruit chemistry in ANCOVA analyses, suggesting no physiological constraints of leaf chemistry on ripe fruit chemistry. Our results suggest that, while maternal plants may vary somewhat in fruit chemistry, and fruit chemistry may vary somewhat depending upon environmental conditions, levels of primary and secondary metabolites within fruits are not best explained by the non-adaptive hypotheses. Ripe fruit chemistry remained relatively constant in the face of drastically changing resource levels, plant growth response, and reproductive output, suggesting an adaptive function, and thus supporting the Optimal Defense hypothesis. Ripe fruit chemistry most likely reflects a balance between selection for attraction and defense.

Key words: carbon-nutrient balance, optimal defense theory, fruit-frugivore interactions, physiologic constraints