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在植物生理生态学中,叶片中碳13(13C)含量负值较少(富集),表明叶片处于通过气孔的气体交换减少,比如在干旱胁迫下.此外,与叶片相比,13C在非光合组织中的负值也较少.然而,对从叶片(光合器官)到树枝、树干和根(非光合器官)中的δ13C数值的关系知之甚少,特别是缺少在关联密切的多个树种间或者不同器官间,以及对生长在极端高温和干旱胁迫下的树木中进行测定.本研究测定了3种近缘沙漠相思树种(Acacia tortilis、A raddiana和A.pachyceras)从叶片到根的13C含量.我们在以色列南部成树的叶片组织中测定了δ13C含量.与此同时,在试验果园进行了为期7年的3个水平的灌溉试验.在试验结束时,测定了叶片、树枝、树干和根的生长参数和δ13C含量.研究结果表明,叶片组织中δ13C含量约为-27‰,其同位素贫化程度远超过生长在地球上最干燥和最热环境中的沙漠树种的预期值.在不同的相思树种和不同器官中,所有灌溉水平处理中的δ13C含量并没有富集(-28‰到ca.-27‰),证实了在成熟相思树中的测定结果.在不同器官中,叶片δ13C含量与树枝和根的δ13C含量异常相似,甚至比树干的δ13C含量负值更少.高度贫化的叶片δ13C表明,尽管这些树木生长在极端干燥的生境中,但其气孔气体交换较高.非光合组织中缺乏δ13C富集可能与叶片和异养组织生长的季节耦合有关.“,”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.