Branchlet nutrient concentration in hoop pine (Araucaria cunninghamii) relative to family, stable carbon and oxygen isotope ratios and growth rate in contrasting environments.

Abstract

Genetic variation in branchlet nutrient (N, P, K, Na, Ca, Mg, Mn and Fe) concentrations and mineral concentration (sum of branchlet P, K, Na, Ca, Mg, Mn and Fe concentrations) of 8-9-year-old hoop pine (Araucaria cunninghamii Ait. ex D. Don) half-sib families was assessed for four canopy positions at a wet site (23 families) and two canopy positions at an N- and water-limiting dry site (22 families) in relation to tree growth and associated branchlet carbon (delta13C) and oxygen (delta18O) isotope composition in southeast Queensland, Australia. Branchlet nutrient and mineral concentrations varied significantly among families and with canopy position and site. Depending on the canopy position sampled, the hoop pine family effect accounted for 0 to 13.8% of the total variation in branchlet N concentration, and for 0 to 30.3% of the total variation in branchlet mineral concentration at the wet site. The corresponding values for the family effect at the dry site were 0-13.3% for branchlet N concentration and 0-25.7% for branchlet mineral concentration. There were significant variations in branchlet P, K, Ca and Mg concentrations at both sites, and these variations differed with canopy position. Relationships between family means of branchlet N concentration and tree growth or delta13C or delta18O varied with canopy position at both sites. At the wet site, there were significant positive correlations between branchlet mineral concentration in the upper-outer or upper-inner canopy and tree height (r = 0.26 and 0.37, P < 0.01) and between branchlet mineral concentration and delta13C (r = 0.24, P < 0.01) in the upper-inner canopy, and a significant negative correlation between branchlet mineral concentration and delta13C (r = -0.21, P < 0.05) in the upper-outer canopy. At the dry site, branchlet mineral concentrations in the upper-inner and upper-outer canopy were significantly correlated with branchlet delta13C (r = -0.28 and -0.51, P < 0.01), and branchlet N concentration in the upper-inner canopy was significantly correlated with tree growth (r = 0.29, P < 0.01). A significant correlation between branchlet delta18O (an index of stomatal conductance) and branchlet mineral concentration at the dry site (r = 0.39, P = 0.020) indicated that stomatal conductance might be a factor regulating the variation in branchlet mineral concentration of the hoop pine families. Both branchlet N concentration and mineral concentration at particular canopy positions assist in selecting hoop pine families with improved tree growth and N- and water-use efficiency in environments where both N deficiency and a limited water supply are major factors affecting plantation productivity.