Date Published:

Abstract:

Aims In plant eco-physiology, less negative (enriched) carbon 13 (C-13) in the leaves indicates conditions of reducing leaf gas exchange through stomata, e.g. under drought. In addition, C-13 is expected to be less negative in non-photosynthetic tissues as compared with leaves. However, these relationships in delta C-13 from leaves (photosynthetic organs) to branches, stems and roots (non-photosynthetic organs) are rarely tested across multiple closely related tree species, multiple compartments, or in trees growing under extreme heat and drought. Methods We measured leaf-to-root C-13 in three closely related desert acacia species (Acacia tortilis, A. raddiana and A. pachyceras). We measured delta C-13 in leaf tissues from mature trees in southern Israel. In parallel, a 7-year irrigation experiment with 0.5, 1.0 or 4.0 L day(-1) was conducted in an experimental orchard. At the end of the experiment, growth parameters and delta C-13 were measured in leaves, branches, stems and roots. Important Findings The delta C-13 in leaf tissues sampled from mature trees was ca. -27 parts per thousand, far more depleted than expected from a desert tree growing in one of the Earth's driest and hottest environments. Across acacia species and compartments, delta C-13 was not enriched at all irrigation levels (-28 parts per thousand to ca. -27 parts per thousand), confirming our measurements in the mature trees. Among compartments, leaf delta C-13 was unexpectedly similar to branch and root delta C-13, and surprisingly, even less negative than stem delta C-13. The highly depleted leaf delta C-13 suggests that these trees have high stomatal gas exchange, despite growing in extremely dry habitats. The lack of delta C-13 enrichment in non-photosynthetic tissues might be related to the seasonal coupling of growth of leaves and heterotrophic tissues.