Relationships between net photosynthesis and foliar nitrogen concentrations in a loblolly pine forest ecosystem grown in elevated atmospheric carbon dioxide

Clint J. Springer, Evan H. DeLucia, Richard B. Thomas

Research output: Contribution to journalArticle

Abstract

We examined the effects of elevated carbon dioxide concentration ([CO 2]) on the relationship between light-saturated net photosynthesis (Asat) and area-based foliar nitrogen (N) concentration (N a) in the canopy of the Duke Forest FACE experiment. Measurements of Asat and Na were made on two tree species growing in the forest overstory and four tree species growing in the forest understory, in ambient and elevated [CO2] FACE rings, during early and late summer of 1999, 2001 and 2002, corresponding to years three, five and six of CO 2 treatment. When measured at the growth [CO2], net photosynthetic rates of each species examined in the forest overstory and understory were stimulated by elevated [CO2] at each measurement date. We found no effect of elevated [CO2] on Na in any of the species. The slope of the Asat-N relationship was 81% greater in elevated [CO2] than in ambient [CO2] when averaged across all sample dates, reflecting a differential CO2 effect on photosynthesis at the top and bottom of the canopy. We compared A sat-N relationships in trees grown in ambient and elevated [CO 2] at two common CO2 concentrations, during late summer 2001 and both early and late 2002, to determine if the stimulatory effect of elevated [CO2] on photosynthesis diminishes over time. At all three sample times, neither the slopes nor the y-intercepts of the Asat-N relationships of trees grown in ambient or elevated [CO2] differed when measured at common CO2 concentrations, indicating that the responses of photosynthesis to long-term elevated [CO2] did not differ from the responses to a short-term increase in [CO2]. This finding, together with the observation that Na was unaffected by growth in elevated [CO2], indicates that these overstory and understory trees growing at the Duke Forest FACE experiment continue to show a strong stimulation of photosynthesis by elevated [CO2].

Original languageEnglish (US)
Pages (from-to)385-394
Number of pages10
JournalTree Physiology
Volume25
Issue number4
DOIs
StatePublished - Apr 2005

Keywords

  • Foliar nitrogen
  • Free Air Carbon Enrichment
  • Loblolly pine forest
  • Net photosynthesis

ASJC Scopus subject areas

  • Physiology
  • Plant Science

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