Nolan Rachael H, Gauthey Alice, Losso Adriano, Medlyn Belinda E, Smith Rhiannon, Chhajed Shubham S, Fuller Kathryn, Song Magnolia, Li Xine, Beaumont Linda J, Boer Matthias M, Wright Ian J, Choat Brendan
Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.
Bushfire Risk Management Research Hub, Wollongong, NSW, 2522, Australia.
New Phytol. 2021 May;230(4):1354-1365. doi: 10.1111/nph.17298. Epub 2021 Apr 3.
Eastern Australia was subject to its hottest and driest year on record in 2019. This extreme drought resulted in massive canopy die-back in eucalypt forests. The role of hydraulic failure and tree size on canopy die-back in three eucalypt tree species during this drought was examined. We measured pre-dawn and midday leaf water potential (Ψ ), per cent loss of stem hydraulic conductivity and quantified hydraulic vulnerability to drought-induced xylem embolism. Tree size and tree health was also surveyed. Trees with most, or all, of their foliage dead exhibited high rates of native embolism (78-100%). This is in contrast to trees with partial canopy die-back (30-70% canopy die-back: 72-78% native embolism), or relatively healthy trees (little evidence of canopy die-back: 25-31% native embolism). Midday Ψ was significantly more negative in trees exhibiting partial canopy die-back (-2.7 to -6.3 MPa), compared with relatively healthy trees (-2.1 to -4.5 MPa). In two of the species the majority of individuals showing complete canopy die-back were in the small size classes. Our results indicate that hydraulic failure is strongly associated with canopy die-back during drought in eucalypt forests. Our study provides valuable field data to help constrain models predicting mortality risk.
2019年，澳大利亚东部经历了有记录以来最热、最干旱的年份。这场极端干旱导致桉树林冠层大量死亡。研究了水力衰竭和树木大小对这三种桉树在干旱期间冠层死亡的作用。我们测量了黎明前和中午的叶片水势（Ψ）、茎干水力导度损失百分比，并量化了干旱诱导木质部栓塞的水力脆弱性。还调查了树木大小和树木健康状况。大部分或全部树叶死亡的树木表现出较高的自然栓塞率（78%-100%）。这与部分冠层死亡的树木（冠层死亡30%-70%：自然栓塞72%-78%）或相对健康的树木（几乎没有冠层死亡迹象：自然栓塞25%-31%）形成对比。与相对健康的树木（-2.1至-4.5MPa）相比，部分冠层死亡的树木中午的Ψ显著更负（-2.7至-6.3MPa）。在其中两个物种中，大多数表现出完全冠层死亡的个体属于小树龄组。我们的结果表明，在桉树林干旱期间，水力衰竭与冠层死亡密切相关。我们的研究提供了有价值的实地数据，有助于限制预测死亡风险的模型。
