|Stipanovic, Robert - Bob|
Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Abstract Only
Publication Acceptance Date: 1/9/2001
Publication Date: N/A
Technical Abstract: Atmospheric CO2 has increased from 270-280 micro liter/l in pre-industrial times, to the current level of 370 micro liter/l. Some scientists project that preindustrial CO2 levels could quadruple. The Carbon/Nutrient Balance Hypothesis (CNB) predicts that plant allocation to defense should reflect the relative availability of both carbon and other nutrients to the plant. Some scientists contend that the CNB hypothesis predicts that plants grown at elevated CO2 levels would allocate relatively more resources to carbon-based defense compounds when compared with plants grown in ambient CO2 levels, while concentrations of nitrogen-based defense compounds would decline. In this study, we measured plant allocation to defensive compounds in cotton plants, under different conditions of carbon (C) and nitrogen (N) availability. We compared C and N levels in cotton plants grown at ambient or elevated CO2, under either low or high N availability. Concentrations of the carbon- based cotton defensive compounds (i.e., total phenolics, condensed tannins, gossypol and related terpenoid aldehydes) and the nitrogen-based compound (i.e., Bt toxin) were measured. The patterns of plant allocation to defensive compounds found in our study were poorly predicted by the CNB hypothesis. The CNB hypothesis was best supported when nitrogen was limiting and carbon was in excess, and least predictive when nitrogen was not limiting. However, our data generally were consistent with the concept that plants are able to shift allocation between N-based and C-based defensive compounds depending on the relative availability of carbon and nitrogen inputs.