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 (δ¹³C), oxygen isotope composition δ¹⁸O), and nitrogen concentration (N_mass) 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 δ¹³C, δ¹⁸O, and N_mass existed among the 9-year-old hoop pine families, with a heritability estimate of 0.72 for branchlet δ¹³C from the upper inner canopy position. There was significant variation in canopy δ¹³C of glasshouse seedlings between canopy positions and among the families, with a heritability estimate of 0.66. The canopy δ¹³C was positively related to canopy N_mass only for the upper outer crown in the field (R = 0.62, p < 0.001). Phenotypic correlations existed between tree height and canopy δ¹³C (R = 0.37-0.41, p < 0.001). Strong correlations were found between family canopy δ¹³C at this site and those at a wetter site and between field canopy δ¹³C and glasshouse seedling δ¹³C. The mechanisms of the variation in canopy δ¹³C are discussed in relation to canopy photosynthetic capacity as reflected in the N_mass and stomatal conductance as indexed by canopy δ¹⁸O.