Canopy carbon and oxygen isotope composition of 9-year-old hoop pine families in relation to seedling carbon isotope composition, growth, field growth performance, and canopy nitrogen concentration

Carbon isotope composition (d13C), oxygen isotope composition (d18O), and nitrogen concentration (Nmass) of branchlet tissue at two canopy positions were assessed for glasshouse seedlings and 9-year-old hoop pine (Araucaria cunninghamii Ait. ex D. Don) trees from 22 open-pollinated families grown in 5 blocks of a progeny test at a water-limited and nitrogen-deficient site in southeastern Queensland, Australia. Significant variations in canopy d13C, d18O, and Nmass existed among the 9-year-old hoop pine families, with a heritability estimate of 0.72 for branchlet d13C from the upper inner canopy position. There was significant variation in canopy d13C of glasshouse seedlings between canopy positions and among the families, with a heritability estimate of 0.66. The canopy d13C was positively related to canopy Nmass only for the upper outer crown in the field (R = 0.62, p < 0.001). Phenotypic correlations existed between tree height and canopy d13C (R = 0.37-0.41, p < 0.001). Strong correlations were found between family canopy d13C at this site and those at a wetter site and between field canopy d13C and glasshouse seedling d13C. The mechanisms of the variation in canopy d13C are discussed in relation to canopy photosynthetic capacity as reflected in the Nmass and stomatal conductance as indexed by canopy d18O.