Hourly and seasonal variation in photosynthesis and stomatal conductance of soybean grown at future CO2 and ozone concentrations for 3 years under fully open-air field conditions

Carl J. Bernacchi, Andrew D.B. Leakey, Lindsey E. Heady, Patrick B. Morgan, Frank G. Dohleman, Justin M. McGrath, Kelly M. Gillespie, Victoria E. Wittig, Alistair Rogers, Stephen P. Long, Donald R. Ort

Research output: Contribution to journalArticlepeer-review

Abstract

It is anticipated that enrichment of the atmosphere with CO2 will increase photosynthetic carbon assimilation in C3 plants. Analysis of controlled environment studies conducted to date indicates that plant growth at concentrations of carbon dioxide ([CO2]) anticipated for 2050 (∼ 550 μmol mol-1) will stimulate leaf photosynthetic carbon assimilation (A) by 20 to 40%. Simultaneously, concentrations of tropospheric ozone ([O3]) are expected to increase by 2050, and growth in controlled environments at elevated [O3] significantly reduces A. However, the simultaneous effects of both increases on a major crop under open-air conditions have never been tested. Over three consecutive growing seasons > 4700 individual measurements of A, photosynthetic electron transport (JPSII) and stomatal conductance (gs) were measured on Glycine max (L.) Merr. (soybean). Experimental treatments used free-air gas concentration enrichment (FACE) technology in a fully replicated, factorial complete block design. The mean A in the control plots was 14.5 μmol m-2 s-1. At elevated [CO2], mean A was 24% higher and the treatment effect was statistically significant on 80% of days. There was a strong positive correlation between daytime maximum temperatures and mean daily integrated A at elevated [CO2], which accounted for much of the variation in CO2 effect among days. The effect of elevated [CO2] on photosynthesis also tended to be greater under water stress conditions. The elevated [O3] treatment had no statistically significant effect on mean A, gs or JPSII on newly expanded leaves. Combined elevation of [CO2] and [O 3] resulted in a slightly smaller increase in average A than when [CO2] alone was elevated, and was significantly greater than the control on 67% of days. Thus, the change in atmospheric composition predicted for the middle of this century will, based on the results of a 3 year open-air field experiment, have smaller effects on photosynthesis, gs and whole chain electron transport through photosystem II than predicted by the substantial literature on relevant controlled environment studies on soybean and likely most other C3 plants.

Original languageEnglish (US)
Pages (from-to)2077-2090
Number of pages14
JournalPlant, Cell and Environment
Volume29
Issue number11
DOIs
StatePublished - Nov 2006

Keywords

  • Air pollution
  • Chlorophyll fluorescence
  • Climate change
  • Free-air gas concentration enrichment (FACE)
  • Global change

ASJC Scopus subject areas

  • Physiology
  • Plant Science

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