Carbon isotope discrimination and oxygen isotope composition in clones of the F-1 hybrid between slash pine and Caribbean pine in relation to tree growth, water-use efficiency and foliar nutrient concentration

The objectives of this study were: (1) to examine how foliar carbon isotope discrimination (Delta) and oxygen isotope composition (delta O-18) are rel ated to tree growth, ash mineral nutrient concentration and foliar nutrient concentration in 7-year-old clones of the F-1 hybrid between slash pine (P inus elliottii Engelm.) and Caribbean pine (P caribaea var. hondurensis Bar r. et Golf.) in subtropical Australia; and (2) to evaluate the potential of using foliar Delta, ash mineral nutrient concentration and delta O-18 meas urements for selecting F-1 hybrid pine clones with high water-use efficienc y (WUE) and growth potential. There were significant differences in tree gr owth, foliar Delta, delta O-18 and ash mineral nutrient concentration among the eight clones tested. Significant negative linear relationships existed between tree growth and Delta, extrapolating to zero growth at Delta = 24- 30 parts per thousand. There were strong genetic correlations (r = -0.83 to -0.96) between Delta and tree growth, particularly tree height. Significan t non-genetic correlations (r = -0.62 to -0.80) existed between Delta and f oliar K concentration. Foliar delta O-18, ash mineral nutrient concentratio n and foliar nutrient concentration were unrelated to tree growth. In the F -1 hybrid pine clones, variation in tree WUE, as reflected by Delta, was la rgely attributed to a genetic effect on leaf photosynthetic capacity rather than on stomatal conductance, as reflected by foliar delta O-18.