Carbon isotope discrimination and oxygen isotope composition in clones of the F1 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}18O) are related to tree growth, ash mineral nutrient concentration and foliar nutrient concentration in 7-year-old clones of the F1 hybrid between slash pine (Pinus elliottii Engelm.) and Caribbean pine (P. caribaea var. hondurensis Barr. et Golf.) in subtropical Australia; and (2) to evaluate the potential of using foliar {Delta}, ash mineral nutrient concentration and {delta}18O measurements for selecting F1 hybrid pine clones with high water-use efficiency (WUE) and growth potential. There were significant differences in tree growth, foliar {Delta}, {delta}18O 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{per thousand}. There were strong genetic correlations (r = –0.83 to –0.96) between {Delta} and tree growth, particularly tree height. Significant non-genetic correlations (r = –0.62 to –0.80) existed between {Delta} and foliar K concentration. Foliar {delta}18O, ash mineral nutrient concentration and foliar nutrient concentration were unrelated to tree growth. In the F1 hybrid pine clones, variation in tree WUE, as reflected by {Delta}, was largely attributed to a genetic effect on leaf photosynthetic capacity rather than on stomatal conductance, as reflected by foliar {delta}18O