School of Ecosystem and Forest Sciences, University of Melbourne, 500 Yarra Blvd, Burnley, VIC, 3121, Australia.
School of Biology, University of Tasmania, 55 Private Bag, Hobart, TAS, 7001, Australia.
Tree Physiol. 2021 Jul 5;41(7):1186-1198. doi: 10.1093/treephys/tpaa176.
Over their lifetime, trees are repeatedly exposed to droughts. It is therefore important to understand whether repeated drought exposure makes trees more or less drought tolerant. Here, we investigated the effect of repeated droughts on functional trait expression and tree function in Eucalyptus obliqua. Further, we tested whether previous drought exposure enabled trees to avoid leaf death for longer under a subsequent severe drought. Trees were subjected for 1 year to 2 drought-rewatering cycles (drought treatment) or well-watered conditions, before imposing a severe drought. Trees in the drought treatment reduced their overall leaf area and biomass, whereas leaf-level anatomical, morphological and physiological traits remained mostly unaffected. There were no differences in water potential at the turgor loss point, leaf xylem vulnerability to embolism, leaf size, maximum xylem vessel diameter or cell wall thickness between treatments after the conditioning period. When exposed to a subsequent severe drought, trees previously exposed to drought were more drought tolerant due to a lower water potential at leaf death and tree-level morphological rather than physiological adjustments. Trees previously exposed to drought were smaller and used less water, which delayed leaf death for 39 days compared with 22 days for the well-watered trees. Our study indicates that previous drought exposure can facilitate tree-level morphological adjustment, which potentially enhances survival of E. obliqua trees during subsequent drought events.
在其一生中，树木会反复遭受干旱。因此，了解反复干旱暴露是否会使树木更能耐受干旱或更不耐旱是很重要的。在这里，我们研究了重复干旱对桉树功能性特征表达和树木功能的影响。此外，我们还测试了先前的干旱暴露是否使树木在随后的严重干旱下能够更长时间地避免叶片死亡。树木在经历为期 1 年的 2 次干旱-复水周期（干旱处理）或充分浇水条件后，再经历严重干旱。干旱处理组的树木整体叶片面积和生物量减少，而叶片水平的解剖学、形态学和生理学特征基本不受影响。在调节期后，处理之间的膨压丧失点水势、叶片木质部对栓塞的脆弱性、叶片大小、最大木质部导管直径或细胞壁厚度没有差异。当暴露于随后的严重干旱时，先前暴露于干旱的树木由于叶片死亡时的水势较低以及树木形态而不是生理调整而更能耐受干旱。先前暴露于干旱的树木较小，用水量较少，与充分浇水的树木相比，叶片死亡延迟了 39 天，而不是 22 天。我们的研究表明，先前的干旱暴露可以促进树木形态的调整，这可能增强桉树在随后的干旱事件中的生存能力。
