Journal Article

Differences in the response sensitivity of stomatal index to atmospheric CO<sub>2</sub> among four genera of Cupressaceae conifers

Matthew Haworth, James Heath and Jennifer C. McElwain

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 105, issue 3, pages 411-418
Published in print March 2010 | ISSN: 0305-7364
Published online January 2010 | e-ISSN: 1095-8290 | DOI:
Differences in the response sensitivity of stomatal index to atmospheric CO2 among four genera of Cupressaceae conifers

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry


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Background and Aims

The inverse relationship between stomatal density (SD: number of stomata per mm2 leaf area) and atmospheric concentration of CO2 ([CO2]) permits the use of plants as proxies of palaeo-atmospheric CO2. Many stomatal reconstructions of palaeo-[CO2] are based upon multiple fossil species. However, it is unclear how plants respond to [CO2] across genus, family or ecotype in terms of SD or stomatal index (SI: ratio of stomata to epidermal cells). This study analysed the stomatal numbers of conifers from the ancient family Cupressaceae, in order to examine the nature of the SI–[CO2] relationship, and potential implications for stomatal reconstructions of palaeo-[CO2].


Stomatal frequency measurements were taken from historical herbarium specimens of Athrotaxis cupressoides, Tetraclinis articulata and four Callitris species, and live A. cupressoides grown under CO2-enrichment (370, 470, 570 and 670 p.p.m. CO2).

Key Results

T. articulata, C. columnaris and C. rhomboidea displayed significant reductions in SI with rising [CO2]; by contrast, A. cupressoides, C. preissii and C. oblonga show no response in SI. However, A. cupressoides does reduce SI to increases in [CO2] above current ambient (approx. 380 p.p.m. CO2). This dataset suggests that a shared consistent SI–[CO2] relationship is not apparent across the genus Callitris.


The present findings suggest that it is not possible to generalize how conifer species respond to fluctuations in [CO2] based upon taxonomic relatedness or habitat. This apparent lack of a consistent response, in conjunction with high variability in SI, indicates that reconstructions of absolute palaeo-[CO2] based at the genus level, or upon multiple species for discrete intervals of time are not as reliable as those based on a single or multiple temporally overlapping species.

Keywords: Carbon dioxide; stomatal density; palaeoclimate; Athrotaxis cupressoides; Tetraclinis articulata; Callitris species; Cupressaceae

Journal Article.  5619 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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