Soybean Responses to Atmospheric Increases in Carbon Dioxide and Ozone

213 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.Atmospheric concentration of carbon dioxide (CO2) has been increasing steadily since the industrial revolution and is expected to double by the middle of this century. Ozone (O3), a secondary air pollutant, has become an issue in the last decades for its damaging effects on humans as well on animals and plants. The effects of elevated carbon dioxide ([CO 2] = 550 mumol mol-1), ozone ([O3] = 1.2 x ambient) and their combination were evaluated in three soybean cultivars from maturation group (MG) II (Corsoy-79, Dwight and Loda) and three cultivars from MG III (Papa, Pioneer 931315 and Williams), using a FACE (Free Air Concentration Enrichment) facility (www.soyface.uiuc.edu). Elevated [CO2] caused an improvement in final plant height and yield components (number of nodes, pods and seeds per plant; seed volume and seed weight), while elevated [O 3] had an opposite effect. Plants grown under elevated [CO2] alone or in combination with elevated [O3] experienced also a delay in senescence and seeds of Loda and Pana demonstrated seed chlorophyll retention at harvest. No changes in seed N or fatty acid content were found due to treatment; however, variation among the years of evaluation was observed. Seed size was strongly correlated to seed C content but not to seed N. Total seed isoflavone content response to treatments was cultivar-dependent, with elevated [CO2] causing an increase in Dwight and Loda and elevated [O 3] causing a decrease in Corsoy and Loda. Isoflavone concentration also varied among the years of evaluation, indicating that other environmental factors influenced plant responses. A reduction in seed Ca and Zn content due to elevated [CO2] and an increase due to elevated [O3 ] was observed in most cultivars evaluated. Results presented also demonstrate that elevated [CO2] mitigates the damages caused by elevated [O 3].U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD