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 is otope discrimination (Delta), survival and growth, to determine the value o f Delta for screening for yield improvement under drought conditions. Intra -specific variation in carbon isotope discrimination (Delta) was examined i n Eucalyptus globulus. Wood samples were collected from 3 to 7 year-old pop ulations from three different field-sites at Huelva (south-western Spain). Differences between study sites were related to the availability of water r esulting from soil physical properties. Average carbon isotope discriminati on ranged from 16.7 to 18.1 parts per thousand. There was a 2.2 parts per t housand maxirnum range in II values among different trees of the same age. A strong, positive correlation was observed between average carbon isotope discrimination and average tree diameter at boast height (DBHob). Average c arbon isotope discrimination was also strongly correlated with survival at the Valdeoscuro site (r(2)=0.95) and with the percentage of failures in nei ghbouring trees (r(2)=0.65) at the San Sebastian site. These results sugges t a strong effect of availability of water on Delta values. Implications fo r the use of carbon isotope discrimination in selecting for better adapted genotypes are discussed. (C) 2001 Elsevier Science B.V. All rights reserved .