title: How does elevated CO2 or ozone affect the leaf-area index of soybean when applied independently?
abstract: Changes in leaf-area index (LAI) may alter ecosystem productivity in elevated [CO2] or [O3]. By increasing the apparent quantum yield of photosynthesis (phi(c,max)), elevated [CO2] may increase maximum LAI. However, [O3] when elevated independently accelerates senescence and may reduce LAI. Large plots (20 m diameter) of soybean (Glycine max) were exposed to ambient (approx. 370 micromol mol(-1)) or elevated (approx. 550 micromol mol(-1)) CO2 or 1.2 times ambient [O3] using soybean free-air concentration enrichment (SoyFACE). In 2001 elevated CO2 had no detectable effect on maximum LAI, but in 2002 maximum LAI increased by 10% relative to ambient air. Elevated [CO2] also increased the phi(c,max) of shade leaves in both years. Elevated [CO2] delayed LAI loss to senescence by approx. 54% and also increased leaf-area duration. Elevated [O3] accelerated senescence, reducing LAI by 40% near the end of the growing season. No effect of elevated [O3] on photosynthesis was detected. Elevated [CO2] or [O3] affected LAI primarily by altering the rate of senescence; knowledge of this may aid in optimizing future soybean productivity.
authors.affiliation: Program in Ecology and Evolutionary Biology, University of Illinois, Urbana, IL 61801, USA.
authors.forename: Orla
authors.initials: O
authors.lastname: Dermody
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Long
authors.forename: Evan H
authors.initials: EH
authors.lastname: DeLucia
mesh_terms: D002245:Carbon Dioxide / Q000494:pharmacology*; D017753:Ecosystem; D009584:Nitrogen / Q000378:metabolism; D010126:Ozone / Q000494:pharmacology*; D010788:Photosynthesis; D018515:Plant Leaves / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D012621:Seasons; D013025:Glycine max / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism
chemical_list: D002245:Carbon Dioxide; D010126:Ozone; D009584:Nitrogen