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Environmental and physiological controls over oxygen and carbon isotope composition of Tasmanian blue gum, Eucalyptus globulus

Cernusak, Lucas A., Farquhar, G. D. and Pate, J. S. (2005). Environmental and physiological controls over oxygen and carbon isotope composition of Tasmanian blue gum, Eucalyptus globulus. Tree Physiology,25(2):129-146.

Document type: Journal Article
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Title Environmental and physiological controls over oxygen and carbon isotope composition of Tasmanian blue gum, Eucalyptus globulus
Author Cernusak, Lucas A.
Farquhar, G. D.
Pate, J. S.
Journal Name Tree Physiology
Publication Date 2005
Volume Number 25
Issue Number 2
ISSN 0829-318X   (check CDU catalogue open catalogue search in new window)
Start Page 129
End Page 146
Total Pages 18
Place of Publication UK
Publisher Oxford University Press
Field of Research 0607 - Plant Biology
0705 - Forestry Sciences
HERDC Category C1 - Journal Article (DEST)
Abstract We measured oxygen isotope ratios (δ18O) of xylem sap, phloem sap, leaves, wood and bark of Eucalyptus globulus Labill. growing in southwestern Australia. Carbon isotope ratios (δ13C) were measured in the dry matter of phloem sap, leaves and wood. Results were used to test several aspects of a mechanistic model of 18Oenrichment and provided insights into post-photosynthetic variations in dry matter δ13C. Xylem water δ18O varied little within the tree crown, whereas variation at the landscape-level was more pronounced, with plantations near the coast being enriched by up to 3‰ compared with plantations less than 100 km inland. Phloem water was significantly enriched in 18O compared with xylem water in two of three sampling campaigns; mean enrichments were 0.5 and 0.8‰. Phloem sap sugars exported from E. globulus leaves closely reflected observed leaf water enrichment when diurnal variation in photosynthesis was taken into account. Photosynthetic rates were higher in the morning than in the afternoon, whereas leaf water 18O enrichment increased to maximum values in the afternoon. A non-steady-state model of leaf water 18O enrichment accurately predicted observed values through a full diel cycle. Mean estimates of the proportion of organic oxygen effectively exchanging with xylem water during cellulose synthesis were close to 0.40 for both leaves and wood. Carbon isotope ratios of nascent xylem tissues did not differ from those of phloem sap sugars collected concurrently, whereas nascent leaf tissues were depleted in 13C by 2‰compared with phloem sap sugars, suggesting that, in E. globulus, 13C enrichment of sink tissues compared with source leaves does not result from an enriching process within the sink tissue.
 
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Created: Wed, 11 Mar 2009, 14:43:24 CST by Sarena Wegener