GENETIC-VARIATION IN CARBON-ISOTOPE DISCRIMINATION AND ITS RELATIONSHIP TO GROWTH UNDER FIELD CONDITIONS IN FULL-SIB FAMILIES OF PICEA-MARIANA

Measurements of the stable carbon isotope composition of leaf tissue w ere made on Picea mariana (Mill.) B.S.P. trees from four full-sit, fam ilies grown on three different field sites at the Petawawa National Fo restry Institute, Ontario, Canada. The four families chosen exhibited genetic variation for growth characteristics. Genetic variation was al so observed for carbon isotopic discrimination (Delta) among the famil ies of P. mariana. In addition, a strong correlation occurred between Delta values measured on trees in 1991 and 1992, two years that had ve ry different precipitation and temperature conditions during the growi ng season, indicating that the ranking of individual trees remained al most constant between years. A strong, negative correlation was observ ed between average carbon isotope discrimination and average tree heig ht for the four families on the driest, least productive site, as was expected based on leaf photosynthetic characteristics. There was no si gnificant correlation, however, between Delta values and growth on the other two study sites, where productivity was higher.