Genetic variation in branchlet carbon and nitrogen isotope composition and nutrient concentration of 11-year-old hoop pine families in relation to tree growth in subtropical Australia

Abstract

Genetic variation in tree growth and branchlet carbon isotope composition (13C), nitrogen (N) isotope composition (15N) and nutrient (N, P, K, Ca, Mg, Mn, Fe, Cu and Zn) concentration of 11-year-old hoop pine (Araucaria cunninghamii Ait. ex D. Don) half-sib families were examined at two contrasting sites (31 families with 8 blocks sampled at a wet site and 27 families with 9 blocks at a dry site) in south-east Queensland, Australia. Genetic correlations were determined between the tree growth traits, between the physiological traits, and between the physiological and growth traits. The potential of using these tree physiological traits was evaluated for assisting in selection of elite hoop pine families with improved water-use efficiency (WUE) as reflected in branchlet 13C, nutrient (particularly N)-use efficiency (NUE) and tree growth. At the wet site there was significant genetic variation in tree growth, branchlet 13C, nutrient concentration and mineral concentration among the 11-year-old hoop pine families, with heritability estimates ranging from 0.26 to 0.72. At the dry site, there was also significant genetic variation in some of the corresponding variables with heritability estimates ranging from 0.26 to 0.54. There seemed to be significant family variation in branchlet 15N at the dry site (P=0.068), with a moderate heritability estimate of 0.21, but not at the wet site. Some strong genetic correlations were also found between the tree growth traits, between the physiological traits, and between the tree growth and the physiological traits. Tree WUE and branchlet nutrient concentrations were significantly influenced by rainfall and soil fertility. Branchlet 15N at the wet site was significantly lower than that at the dry site, suggesting that soil microbial–plant interactions might play a role in discriminating soil available 15N in favor of 14N for tree uptake (lower 15N in plant tissues) at the wet site. Branchlet 13C 15N and nutrient (particularly N) concentration show promise as physiological and nutritional traits for assisting in the selection of elite hoop pine families with improved tree WUE, NUE and growth for the more water- and nutrient-limited environments in subtropical Australia.