Variation in branchlet δ13C in relation to branchlet nitrogen concentration and growth in 8-year-old hoop pine families (Araucaria cunninghamii) in subtropical Australia

Abstract

Carbon isotope composition (δ13C) of branchlet tissue at nine canopy positions, and nitrogen concentration (Nmass) at four canopy positions, were assessed in 8-year-old hoop pine (Araucaria cunninghamii Ait. ex D. Don) trees from 23 half-sib families, grown in six blocks of a progeny test in southeastern Queensland, Australia. There was considerable variation among sampling positions, families and blocks in both δ13C and Nmass. The δ13C was positively related to Nmass only for samples from the upper outer crown (P < 0.005). Phenotypic correlations existed between tree growth and canopy δ13C. Branchlet δ13C of the inner and lower outer crown was positively related (P < 0.037) to tree height, but δ13C in branchlets of the upper outer crown was not related to tree height, or was related negatively (P < 0.045). There were significant differences in δ13C between hoop pine families for six canopy positions (upper canopy positions as well as lower canopy positions on the northern side), with heritabilities greater than 0.40. The significance of these findings is discussed in relation to water and light competition within the tree canopy of hoop pine.