Carbon isotope discrimination by a sequence of Eucalyptus species along a subcontinental rainfall gradient in Australia

Authors

  • J. M. MIller,

    1. Environmental Biology Group,
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  • R. J. Williams,

    1. CSIRO Division of Wildlife and Ecology, and Co-operative Research Centre for Tropical Savannas, PMB Box 44, Winnellie, NT 0822, Australia
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  • G. D. Farquhar

    1. Environmental Biology Group,
    2. Co-operative Research Centre for Greenhouse Accounting, Research School of Biological Sciences, Institute of Advanced Studies, Australian National University, GPO Box 475, Canberra, ACT 2601, Australia, and
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    • Author to whom correspondence should be addressed.


Abstract

1. The 13C/12C discrimination (Δ) by a series of co-occurring and replacement Eucalyptus species was measured across an eightfold decrease in rainfall. As Δ is a measure of the stomatal limitation on photosynthesis, it should provide a subcontinental scale measure of water-limited plant physiological performance.

2. Leaf Δ of five of 13 species decreased with decreasing rainfall, seven exhibited no trend, and one increased. Wood Δ decreased in eight species, showed no trend in four, and increased in one species.

3. Species replacements were marked by a shift in Δ reflecting greater stomatal limitation on carbon assimilation.

4. Wood Δ was less variable than leaf Δ.

5. There was a non-linear response of the multispecies average leaf and wood Δ to decreasing total annual rainfall. This response reflected the spatial pattern of the sensitivities of Δ to decreasing rainfall of the individual species. It was not the result of a proposed emergent behaviour where the trend in the multispecies average differed from that of the individual species.

6. Patterns of Δ across the distributions of species (reflecting increasing stomatal limitation on assimilation) did not provide a simple measure of the physiological limits of the distribution of eucalypts in north-western Australia.

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