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

1. The ¹³C/¹² 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 °. 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.