Los Alamos National Laboratory, Earth and Environmental Sciences Division (EES-14) MS J495, Los Alamos, NM, 87545-1663, USA.
Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, MD, 21037-0028, USA.
New Phytol. 2021 Sep;231(5):1798-1813. doi: 10.1111/nph.17464. Epub 2021 Jul 2.
Deep-water access is arguably the most effective, but under-studied, mechanism that plants employ to survive during drought. Vulnerability to embolism and hydraulic safety margins can predict mortality risk at given levels of dehydration, but deep-water access may delay plant dehydration. Here, we tested the role of deep-water access in enabling survival within a diverse tropical forest community in Panama using a novel data-model approach. We inversely estimated the effective rooting depth (ERD, as the average depth of water extraction), for 29 canopy species by linking diameter growth dynamics (1990-2015) to vapor pressure deficit, water potentials in the whole-soil column, and leaf hydraulic vulnerability curves. We validated ERD estimates against existing isotopic data of potential water-access depths. Across species, deeper ERD was associated with higher maximum stem hydraulic conductivity, greater vulnerability to xylem embolism, narrower safety margins, and lower mortality rates during extreme droughts over 35 years (1981-2015) among evergreen species. Species exposure to water stress declined with deeper ERD indicating that trees compensate for water stress-related mortality risk through deep-water access. The role of deep-water access in mitigating mortality of hydraulically-vulnerable trees has important implications for our predictive understanding of forest dynamics under current and future climates.
深水位获取可以说是植物在干旱期间生存的最有效但研究不足的机制。栓塞脆弱性和水力安全裕度可以预测在给定脱水水平下的死亡率风险，但深水位获取可能会延迟植物脱水。在这里，我们使用一种新的数据模型方法，在巴拿马的一个多样化的热带森林群落中测试了深水位获取在生存中的作用。我们通过将直径生长动态（1990-2015 年）与蒸汽压亏缺、整个土壤柱中的水势和叶片水力脆弱性曲线联系起来，反演了 29 种冠层物种的有效根深度（ERD，即水提取的平均深度）。我们将 ERD 估计值与现有的潜在水获取深度的同位素数据进行了验证。在物种间，较深的 ERD 与较高的最大茎水力传导率、对木质部栓塞的更大脆弱性、更窄的安全裕度以及在 35 年（1981-2015 年）的极端干旱中常绿物种的死亡率较低有关。物种对水胁迫的暴露随着 ERD 的加深而降低，这表明树木通过深水位获取来补偿与水胁迫相关的死亡率风险。深水位获取在减轻水力脆弱性树木死亡率方面的作用对我们在当前和未来气候下对森林动态的预测理解具有重要意义。
