• Changes in leaf-area index (LAI) may alter ecosystem productivity in elevated [CO 2 ] or [O 3 ]. By increasing the apparent quantum yield of photosynthesis (φ c,max ), elevated [CO 2 ] may increase maximum LAI. However, [O 3 ] when elevated independently accelerates senescence and may reduce LAI. • Large plots (20 m diameter) of soybean (Glycine max) were exposed to ambient (approx. 370 μmol mol -1 ) or elevated (approx. 550 μmol mol -1 ) CO 2 or 1.2 times ambient [O 3 ] using soybean free-air concentration enrichment (SoyFACE). • In 2001 elevated CO 2 had no detectable effect on maximum LAI, but in 2002 maximum LAI increased by 10% relative to ambient air. Elevated [CO 2 ] also increased the φ c,max of shade leaves in both years. Elevated [CO 2 ] delayed LAI loss to senescence by approx. 54% and also increased leaf-area duration. Elevated [O 3 ] accelerated senescence, reducing LAI by 40% near the end of the growing season. No effect of elevated [O 3 ] on photosynthesis was detected. • Elevated [CO 2 ] or [O 3 ] affected LAI primarily by altering the rate of senescence; knowledge of this may aid in optimizing future soybean productivity.

Original languageEnglish (US)
Pages (from-to)145-155
Number of pages11
JournalNew Phytologist
Issue number1
StatePublished - Jan 1 2006


  • Leaf-area index (LAI)
  • Senescence
  • SoyFACE (soybean free-air concentration enrichment)
  • Soybean (Glycine max)

ASJC Scopus subject areas

  • Physiology
  • Plant Science

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