Soybean Responses to Atmospheric Increases in Carbon Dioxide and Ozone

Abstract

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].