Dry mass allocation, water use efficiency and 13C in clones of Eucalyptus grandis, E. grandis x camaldulensis and E. grandis x nitens grown under two irrigation regimes

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Abstract
Clonal variation in water use efficiency (WUE), dry mass accumulation and allocation, and stable carbon isotope ratio (δ13C) of crude leaf fiber extracts was determined in six clones of Eucalyptus grandis W. Hill ex Maiden. grown for 16 months in field lysimeters in two soil water regimes. The relationships between δ13C and WUE calculated on the basis of leaf, harvestable stem, shoot and whole-plant dry mass accumulation were investigated. There was no clonal variation in dry mass accumulation but clonal allocation to roots, harvestable stems, branches and leaves varied. Water use efficiencies (mass of plant or plant part/water used over 16 months) differed significantly between clones. The clonal ranking of WUE varied depending on the units of dry mass accumulation used. Significant relationships between δ13C values and instantaneous water use efficiencies and ratios of internal leaf to ambient CO2 concentrations were found only in the high soil water treatment. There were no relationships between δ13C values and whole-plant, shoot and harvestable stem water use efficiencies and soil water availability. Values of δ13C were negatively correlated with dry mass accumulation in the low soil water treatment. At the whole-plant level, WUE was positively correlated with dry mass accumulation in the high soil water treatment. We found significant differences in δ13C values between clones and the clonal rankings in δ13C and WUE were maintained in both soil water treatments.

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