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 CO 2 concentration ([CO 2 ]). 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 CO 2 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 [CO 2 ] 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 [CO 2 ] 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 [CO 2 ] plots, respectively. The 27% increase in ε in response to CO 2 enrichment was caused primarily by the stimulation of biomass increment, as there was only a small effect of elevated [CO 2 ] on L* during the initial years of fumigation. Long-term increases in atmospheric [CO 2 ] 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

Fingerprint

radiation use efficiency
Pinus taeda
Carbon Monoxide
Carbon Dioxide
carbon dioxide
Radiation
Biomass
hardwood
biomass production
forest canopy
dry matter partitioning
Fumigation
photosynthetically active radiation
fumigation
tree growth
leaf area index
aboveground biomass
understory
Forests
leaves

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

Cite this

Radiation-use efficiency of a forest exposed to elevated concentrations of atmospheric carbon dioxide. / DeLucia, Evan H.; George, Kate; Hamilton, Jason G.

In: Tree Physiology, Vol. 22, No. 14, 10.2002, p. 1003-1010.

Research output: Contribution to journalArticle

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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 CO 2 concentration ([CO 2 ]). 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 CO 2 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 [CO 2 ] 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 [CO 2 ] 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 [CO 2 ] plots, respectively. The 27{\%} increase in ε in response to CO 2 enrichment was caused primarily by the stimulation of biomass increment, as there was only a small effect of elevated [CO 2 ] on L* during the initial years of fumigation. Long-term increases in atmospheric [CO 2 ] can increase ε in closed-canopy forests but the absolute magnitude and duration of this increase remain uncertain.",
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