Physiological influences on carbon isotope discrimination in Huon Pine (Lagarstrobos franklinii)

Robert Francey, Roger Gifford, Tom Sharkey, B Weir

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Abstract

Measurements of the light environment and stomatal and photosynthetic behaviour are reported for Huon Pine (Lagarostrobos franklinii, family Podocarpaceae) in western Tasmanian rainforest. For a variety of microenvironments, these are used in an analysis of stable carbon isotope measurements in the air, and in branch and leaf material, using a model for carbon isotope fractionation in leaves (Farquhar et al. 1982).
The major features of δ13C variations with respect to branch position can be explained in terms of the direct influence of light level acting via the rate of CO2 assimilation. In addition a relatively constant δ13C gradient of about 2.6‰ between leaf tip and branch wood is observed.

Alternative explanations are advanced for the tip-towood gradient in δ13C. If the δ13C of leaf tips is taken to represent the value for photosynthate, maintenance respiration is proposed as a mechanism for the further fractionation; a significant 13C depletion in respired CO2 is implied which is not supported by indirect measurements of atmospheric isotope ratio. Furthermore, an assumption of significant sampling errors (e.g. related to humidity effects on assimilation) is required to obtain good quantitative prediction of the light influence.

If the branch wood δ13C is taken to represent that of the photosynthate, the tip-to-wood gradient may find an explanation, via the model, in terms of tip tissue comprising carbon from immature cells. Translocation of photosynthate from exposed to shaded branches is then proposed as a means of obtaining quantitative agreement with the predicted light influence.

The support provided for the applicability of the Farqunar et al. (1982) model in the field is discussed in the context of the problem of obtaining past global atmospheric CO2 levels from δ13C in tree-rings.
Original languageEnglish
Pages (from-to)211 - 218
Number of pages7
JournalOecologia
Volume66
Issue number2
DOIs
Publication statusPublished - 1985

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carbon isotope
isotopes
photosynthates
Pinus
branchwood
carbon
carbon dioxide
leaves
assimilation (physiology)
fractionation
Podocarpaceae
isotope fractionation
growth rings
cell respiration
tree ring
rainforest
translocation
rain forests
humidity
stable isotope

Cite this

Francey, Robert ; Gifford, Roger ; Sharkey, Tom ; Weir, B. / Physiological influences on carbon isotope discrimination in Huon Pine (Lagarstrobos franklinii). In: Oecologia. 1985 ; Vol. 66, No. 2. pp. 211 - 218.
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Physiological influences on carbon isotope discrimination in Huon Pine (Lagarstrobos franklinii). / Francey, Robert; Gifford, Roger; Sharkey, Tom; Weir, B.

In: Oecologia, Vol. 66, No. 2, 1985, p. 211 - 218.

Research output: Contribution to journalArticle

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T1 - Physiological influences on carbon isotope discrimination in Huon Pine (Lagarstrobos franklinii)

AU - Francey, Robert

AU - Gifford, Roger

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AB - Measurements of the light environment and stomatal and photosynthetic behaviour are reported for Huon Pine (Lagarostrobos franklinii, family Podocarpaceae) in western Tasmanian rainforest. For a variety of microenvironments, these are used in an analysis of stable carbon isotope measurements in the air, and in branch and leaf material, using a model for carbon isotope fractionation in leaves (Farquhar et al. 1982).The major features of δ13C variations with respect to branch position can be explained in terms of the direct influence of light level acting via the rate of CO2 assimilation. In addition a relatively constant δ13C gradient of about 2.6‰ between leaf tip and branch wood is observed.Alternative explanations are advanced for the tip-towood gradient in δ13C. If the δ13C of leaf tips is taken to represent the value for photosynthate, maintenance respiration is proposed as a mechanism for the further fractionation; a significant 13C depletion in respired CO2 is implied which is not supported by indirect measurements of atmospheric isotope ratio. Furthermore, an assumption of significant sampling errors (e.g. related to humidity effects on assimilation) is required to obtain good quantitative prediction of the light influence.If the branch wood δ13C is taken to represent that of the photosynthate, the tip-to-wood gradient may find an explanation, via the model, in terms of tip tissue comprising carbon from immature cells. Translocation of photosynthate from exposed to shaded branches is then proposed as a means of obtaining quantitative agreement with the predicted light influence.The support provided for the applicability of the Farqunar et al. (1982) model in the field is discussed in the context of the problem of obtaining past global atmospheric CO2 levels from δ13C in tree-rings.

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