Direct and Indirect Effects of Elevated Carbon Dioxide and Ozone on the Canopy of a Soybean Agroecosystem

126 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.It is unknown how rising atmospheric CO2 and O3 will directly and indirectly alter canopy structure and scale to affect ecosystems. I determined how leaf area index (LAI) was directly affected by elevated [CO 2] and [O3]. By increasing photosynthetic efficiency, elevated [CO2] may increase maximum LAI. However, [O3] accelerates senescence and may reduce LAI. My second objective was to determine how changes in canopy size altered the radiation use efficiency of the canopy in elevated [CO2] and [O3]. Radiation use efficiency (&egr;) is a measure of the conversion efficiency of absorbed radiation (APAR) into biomass. I expected elevated [CO2] to increase &egr; however, elevated [O3] may have the opposite effect. Folivorous insects indirectly reduce canopy size through the removal of leaf area, and the changes in leaf chemistry in elevated [CO2] and [O3] may lead to increased herbivory. These predictions were tested using Soy bean F&barbelow;ree-A&barbelow;ir C&barbelow;oncentration E&barbelow;nrichment technology (SoyFACE) with plots exposed to ambient air (∼370ppm), elevated CO2 (∼550ppm) and elevated O3 (1.2*ambient). Elevated [CO2] increased maximum LAI and delayed LAI loss to senescence, although the effects varied among years. Elevated [O3] consistently reduced LAI by accelerating senescence. These effects combined with corresponding changes in biomass, to increase &egr; in elevated [CO2] and reduce &egr; in elevated [O3]. Increased &egr; in elevated [CO2] was driven primarily by increased biomass however, in elevated [O3] increased LAI loss to senescence droves decrease in biomass. Growth in elevated [CO2] increased the susceptibility of soybeans to herbivory, particularly by non-native insects. Chronic exposure to elevated [O3] produced few significant effects on herbivory. The impacts of altered tropospheric chemistry on soybeans will be complicated by the complex behavior of insect pests and their indirect effects on plant canopies and productivity.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD