PARENT SESSION
Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.

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

Changes in plant elemental ratios in response to increased CO₂ and nitrogen enrichment.

Novotny, Amy^*,1, Schade, John^{*,1, 2}, Kay, Adam², Hernandez, Daniel², Ogdahl, Megan², Hobbie, Sarah², ¹ Arizona State University, Tempe, Arizona² University of Minnesota, St. Paul, Minnesota

ABSTRACT- Human activities have resulted in increased nitrogen deposition and atmospheric CO₂ concentrations, potentially causing significant changes in nutrient cycling rates in human-dominated ecosystems. Specifically, increased nitrogen and carbon availability may lead to phosphorus limitation of key ecosystem processes. We tested this hypothesis using a fully-crossed CO₂ and N enrichment experiment (BioCON at Cedar Creek Natural History Area, Minnesota), focusing on variation in tissue chemistry of herbaceous plant species. Here we present results from monocultures of two species, Solidago rigida and Amorpha canescens, a leguminous forb. We predicted higher C:P and N:P ratios in plants receiving elevated CO₂ and N deposition, indicating that P has become the limiting resource. We found significantly higher C:P ratios in Solidago plots receiving both C and N enrichment than in all other treatments. Monocultures of Amorpha showed lower C:P in all C enriched plots and showed no response to N additions. In both species, N:P decreased under C enrichment. In Solidago plots, N:P increased under N enrichment, while the effects of simultaneous enrichment with C and N were additive. When combined with recent data showing a significant influence of changes in plant C:P and N:P on insect herbivores, these data suggest the potential for an important influence of human activities on food web dynamics mediated by changes in food quality.

Key words: CO2 enrichment, nitrogen deposition