Stable carbon isotope discrimination: an indicator of cumulative salinity and boron stress in Eucalyptus camaldulensis

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Abstract
Saplings of Eucalyptus camaldulensis Dehn. Clone 4544, irrigated with water of differing salinities (2 to 28 dS m−1) and boron concentrations (1 to 30 mg l−1), integrated the history of these stresses through the discrimination of stable isotopes of carbon in leaf and woody tissues. Carbon isotope discrimination (Δ) was reduced primarily by salinity. Decreases in discrimination in response to boron stress were detected in the absence of salinity stress, but the decreases were significant only in leaf tissues with visible boron injury. Sapwood core samples indicated that salinity- and boron-induced reductions in Δ increased with increasing tree age. Absolute values of Δ varied with location of leaf or wood tissue, but relative effects of salinity on the relationship between Δ and transpiration efficiency (W) were similar. In response to increasing salinity stress, relative decreases in Δ paralleled relative decreases in biomass and both indices yielded similar salt tolerance model parameters. The strong correlations between Δ, tree fresh weight, leaf area and W suggest that Δ is a useful parameter for evaluating salt tolerance of eucalypts.

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