Chloride content and biomass partitioning in Eucalyptus hybrids grown on saline sites

Eucalyptus camaldulensis x globulus and E. camaldulensis x grandis hybrids have been developed to combine the salt-waterlogging tolerance and high-quality wood fibre of their respective parents. The aim is to develop trees that will grow in relatively dry and/or saline environments and provide commercial wood products. Previous studies indicate that the hybrids exhibit faster growth than either of their pure species parents, and that there are significant differences in growth rates between them. We undertook a comparative study of the partitioning of above-ground biomass (AGB) to examine biomass and chloride (Cl) allocation of trees growing on two saline-irrigated sites in south-eastern Australia. Eucalyptus camaldulensis x globulus had a higher proportion of AGB in leaves (20-29% cf. 15-16%), and lower proportion in live branches (3-10% cf. 6-14%) than E. camaldulensis x grandis. The concentration of Cl was highest in the stembark (4.2-9.6 g kg(-1)) and lowest in the stemwood (0.6-2.0 g kg(-1)), suggesting that trees can export Cl through bark shedding. Total Cl content was strongly related to volume under bark (R(2) = 0.99), and differences in partitioning of Cl into tree components differed between the hybrids in the same way as AGB. Preferential partitioning of Cl to live branches rather than foliage in E. camaldulensis x grandis suggests that this hybrid may be compartmentalising Cl to reduce the risk of Cl toxicity in the leaves.