Carbon isotope discrimination and its relationship to drought resistance under field conditions in genotypes of Eucalyptus globulus Labill.

The aim of this study was to investigate the relationship between carbon isotope discrimination (Δ), survival and growth, to determine the value of Δ for screening for yield improvement under drought conditions. Intra-specific variation in carbon isotope discrimination (Δ) was examined in Eucalyptus globulus. Wood samples were collected from 3 to 7 year-old populations from three different field-sites at Huelva (south-western Spain). Differences between study sites were related to the availability of water resulting from soil physical properties. Average carbon isotope discrimination ranged from 16.7 to 18.1‰. There was a 2.2‰ maximum range in Δ values among different trees of the same age. A strong, positive correlation was observed between average carbon isotope discrimination and average tree diameter at breast height (DBH_ob). Average carbon isotope discrimination was also strongly correlated with survival at the Valdeoscuro site (r²=0.95) and with the percentage of failures in neighbouring trees (r²=0.65) at the San Sebastián site. These results suggest a strong effect of availability of water on Δ values. Implications for the use of carbon isotope discrimination in selecting for better adapted genotypes are discussed.