Radiation-use efficiency of a forest exposed to elevated concentrations of atmospheric carbon dioxide

Evan H. DeLucia, Kate George, Jason G. Hamilton

Research output: Contribution to journalArticle

Abstract

We compared radiation-use efficiency of growth (ε), defined as rate of biomass accumulation per unit of absorbed photosynthetically active radiation, of forest plots exposed to ambient (̃360 μl l-1) or elevated (̃560 μl l-1) atmospheric CO2 concentration ([CO2]). Large plots (30-m diameter) in a loblolly pine (Pinus taeda L.) plantation, which contained several hardwood species in the understory, were fumigated with a free-air CO2 enrichment system. Biomass accumulation of the dominant loblolly pines was calculated from monthly measurements of tree growth and site-specific allometric equations. Depending on the species, leaf area index (L*) was estimated by three methods: optical, allometric and litterfall. Based on the relationship between tree height and diameter during the first 3 years of exposure, we conclude that elevated [CO2] did not alter the pattern of aboveground biomass allocation in loblolly pine. There was considerable variation in L* estimates by the different methods; total L* was 18-42% lower when estimated by the optical method compared with estimates from allometric calculations, and this discrepancy was reduced when optical measurements were corrected for the non-random distribution of loblolly pine foliage. The allometric + litterfall approach revealed a seasonal maximum total L* of 6.2-7.1 with about 1/3 of the total from hardwood foliage. Elevated [CO2] had only a slight effect on L* in the first 3 years of this study. Mean ε (± SD), calculated for loblolly pine only, was 0.49 ± 0.05 and 0.62 ± 0.04 g MJ-1 for trees in the ambient and elevated [CO2] plots, respectively. The 27% increase in ε in response to CO2 enrichment was caused primarily by the stimulation of biomass increment, as there was only a small effect of elevated [CO2] on L* during the initial years of fumigation. Long-term increases in atmospheric [CO2] can increase ε in closed-canopy forests but the absolute magnitude and duration of this increase remain uncertain.

Original languageEnglish (US)
Pages (from-to)1003-1010
Number of pages8
JournalTree Physiology
Volume22
Issue number14
DOIs
StatePublished - Oct 2002

Keywords

  • Absorbed photosynthetically active radiation
  • Biomass increment
  • Free-air CO enrichment
  • Leaf area index
  • Loblolly pine
  • Pinus taeda

ASJC Scopus subject areas

  • Physiology
  • Plant Science

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