Effects of branch length on carbon isotope discrimination in Pinus radiata

Abstract

Gas exchange was measured on a pruned Pinus radiata D. Don hedge and on a long-branch P. radiata tree near Hamilton, New Zealand, in spring 1993 when soil water content was close to field capacity. Foliage at the end of long branches (9.0 m) showed a marked drop in net photosynthetic rate and stomatal conductance as the saturation deficit increased, whereas foliage on short branches (0.5 m) showed little change. Mean foliage δ13C was -30.1‰ for short branches and -26.3‰ for long branches. Foliage δ13C was correlated with branch length in two genetically improved P. radiata seedlots at four stocking densities. The multinodal seedlot had shorter branches and more 13C-depleted foliage compared with branches and foliage from the long internode seedlot. There was a strong effect of stocking density on carbon isotope composition in both seedlots. We conclude that branch morphology affects foliage gas exchange properties and foliage carbon isotope composition.