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

Abstract

The objectives of this study were: (1) to examine how foliar carbon isotope discrimination (Δ) and oxygen isotope composition (δ18O) 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 Δ, ash mineral nutrient concentration and δ18O measurements for selecting F1 hybrid pine clones with high water-use efficiency (WUE) and growth potential. There were significant differences in tree growth, foliar Δ, δ18O and ash mineral nutrient concentration among the eight clones tested. Significant negative linear relationships existed between tree growth and Δ, extrapolating to zero growth at Δ = 24–30‰. There were strong genetic correlations (r = –0.83 to –0.96) between Δ and tree growth, particularly tree height. Significant non-genetic correlations (r = –0.62 to –0.80) existed between Δ and foliar K concentration. Foliar δ18O, 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 Δ, was largely attributed to a genetic effect on leaf photosynthetic capacity rather than on stomatal conductance, as reflected by foliar δ18O.