The University of Queensland, School of Biological Sciences, Brisbane, Queensland 4072, Australia.
University of Washington, Biology Department, Seattle, WA 98195-1800, USA.
Tree Physiol. 2018 May 1;38(5):664-677. doi: 10.1093/treephys/tpx143.
Functional traits associated with drought resistance can be useful for predicting tree responses to a drying climate. Yet drought resistance is likely achieved through a complex combination of constitutive traits (traits expressed even in benign environments) and plastic traits (traits expressed only in response to drought). Because few studies measure multiple traits for multiple species under both well-watered and drought conditions, we often struggle to identify suites of constitutive and plastic traits indicative of drought resistance strategies. Using a greenhouse experiment, we examined nine drought resistance traits (six morphological/allocation traits plus assimilation, stomatal conductance and water-use efficiency) in well-watered and water-stressed seedlings of four Brachychiton (Malvaceae Juss.) species with ranges spanning a strong aridity gradient in east-central Australia. In benign conditions, constitutive biomass allocation was consistent with expectations, with xeric species investing more heavily in roots and stem tissue and less in leaf tissue than mesic species (P = 0.004). Under drought conditions, xeric species decreased relative biomass allocation below-ground while mesic species increased relative below-ground allocation (treatment × species interaction P = 0.0015). Relative water content of the stems was slightly higher in xeric species (P = 0.055), and remained stable during drought while decreasing in mesic species (treatment × species P = 0.001). Specific leaf area (SLA) and leaf dry matter content (LDMC) did not fit with expectations under either benign or water-limited conditions. Moreover, stomatal conductance and carbon assimilation were unexpectedly highest and intrinsic water-use efficiency (WUEi) lowest in the xeric species in benign conditions. Only under drought did the xeric species manifest higher WUEi than the mesic species (treatment × species P < 0.0001). We found that even closely related species exhibited diverse combinations of drought resistance traits. Notably, traits commonly used as proxies for drought tolerance (e.g., SLA, LDMC, well-watered WUEi) performed more poorly than constitutive allocation traits. This study highlights the need to consider multiple traits and phenotypic plasticity when assessing species' drought resistance for forest management in the face of climate change.
与抗旱性相关的功能特征可用于预测树木对干燥气候的反应。然而，抗旱性可能是通过组成型特征（即使在良性环境中也表达的特征）和塑性特征（仅在应对干旱时表达的特征）的复杂组合来实现的。由于很少有研究在充分浇水和干旱条件下测量多个物种的多个特征，因此我们常常难以确定代表抗旱策略的组成型和塑性特征的特征。我们使用温室实验，研究了澳大利亚中东部干旱梯度跨度较大的四个 Brachychiton（锦葵科 Juss.）物种的幼苗在充分浇水和水分胁迫下的九个抗旱特征（六个形态/分配特征加上同化、气孔导度和水分利用效率）。在良性条件下，组成型生物量分配与预期一致，干旱物种比湿润物种更倾向于在根系和茎组织中投入更多，而在叶片组织中投入更少（P = 0.004）。在干旱条件下，干旱物种的地下生物量分配相对减少，而湿润物种的地下分配相对增加（处理×物种互作 P = 0.0015）。茎的相对含水量在干旱物种中略高（P = 0.055），在干旱期间保持稳定，而在湿润物种中则下降（处理×物种 P = 0.001）。在良性或水分限制条件下，比叶面积（SLA）和叶干物质含量（LDMC）都不符合预期。此外，在良性条件下，干旱物种的气孔导度和碳同化最高，而内在水分利用效率（WUEi）最低。只有在干旱条件下，干旱物种的 WUEi 才高于湿润物种（处理×物种 P < 0.0001）。我们发现，即使是密切相关的物种也表现出抗旱特征的多种组合。值得注意的是，通常用作耐旱性指标的特征（例如 SLA、LDMC、充分浇水 WUEi）的表现不如组成型分配特征。本研究强调，在应对气候变化时，需要考虑多个特征和表型可塑性来评估物种的抗旱性，以便进行森林管理。
