Unexpectedly low δ13C in leaves, branches, stems and roots of three acacia species growing in hyper-arid environments

Aims In plant eco-physiology,less negative (enriched) carbon 13 (13C) in the leaves indicates conditions of reducing leaf gas exchange through stomata,e.g.under drought.In addition,13C is expected to be less negative in non-photosynthetic tissues as compared with leaves.However,these relationships in δ13C 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 13C in three closely related desert acacia species (Acacia tortilis,A.raddiana and A.pachyceras).We measured δ13C 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 δ13C were measured in leaves,branches,stems and roots.Important Findings The δ13C in leaf tissues sampled from mature trees was ca.-27‰,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,δ13C was not enriched at all irrigation levels (-28‰ to ca.-27‰),confirming our measurements in the mature trees.Among compartments,leaf δ13C was unexpectedly similar to branch and root δ13C,and surprisingly,even less negative than stem δ13C.The highly depleted leaf δ13C suggests that these trees have high stomatal gas exchange,despite growing in extremely dry habitats.The lack of δ13C enrichment in non-photosynthetic tissues might be related to the seasonal coupling of growth of leaves and heterotrophic tissues.