Date of Award


Degree Name

Master of Science


Biological Sciences

First Advisor

Dr. David Karowe

Second Advisor

Dr. Alexander Enyedi

Third Advisor

Dr. Stephen Malcolm

Fourth Advisor

Dr. Sylvia Rossbach

Access Setting

Masters Thesis-Open Access


Wild-type and non-nodulated soybean were grown at 367 ± 10 ppm [ambient] and 756 ± 10 ppm [elevated] CO2 to determine whether nitrogen fixation could minimize the effects of elevated CO2 on plant nutritional and defensive chemistry. Relative to non-nodulated soybean, wild-type soybean had higher concentrations of leaf nitrogen and proteinase inhibitors, as well as lower C:N ratios and lower phenolics. Elevated CO2 resulted in decreased leaf nitrogen and proteinase inhibitor contents, and increased C:N ratios and phenolics in both soybean strains. Constitutive levels of phenolics and proteinase inhibitors occurred as predicted by the Carbon/Nutrient Balance hypothesis (Bryant et al., 1983). However, induction of phenolics only occurred in plants grown at ambient CO2, and induction of trypsin inhibitors only occurred in wild-type plants. Nodulation had the greatest effect on performance of P. includens; larvae fed non-nodulated plants displayed lower consumption, digestion, and growth rates. Increased larval consumption of elevated CO2-grown plants was sufficient to prevent decreased growth, suggesting that host-plant association with nitrogen-fixing symbionts may buffer this legume-feeding insect against CO2-induced changes in host plant chemistry.

Included in

Biology Commons