Accurate understanding of plant responses to water stress is increasingly important for quantification of ecosystem carbon and water cycling under future climates. Plant water-use strategies can be characterized across a spectrum of water stress responses, from tight stomatal control (isohydric) to distinctly less stomatal control (anisohydric). A recent and popular classification method of plant water-use strategies utilizes the regression slope of predawn and midday leaf water potentials, σ, to reflect the coupling of soil water availability (predawn leaf water potential) and stomatal dynamics (daily decline in leaf water potential). This type of classification is important in predicting ecosystem drought response and resiliency. However, it fails to explain the relative stomatal responses to drought of Acer sacharrum and Quercus alba, improperly ranking them on the spectrum of isohydricity. We argue this inconsistency may be in part due to the cuticular conductance of different species. We used empirical and modeling evidence to show that plants with more permeable cuticles are more often classified as anisohydric; the σ values of those species were very well correlated with measured cuticular permeance. Furthermore, we found that midday leaf water potential in species with more permeable cuticles would continue to decrease as soils become drier, but not in those with less permeable cuticles. We devised a diagnostic parameter, Γ, to identify circumstances where the impact of cuticular conductance could cause species misclassification. The results suggest that cuticular conductance needs to be considered to better understand plant water-use strategies and to accurately predict forest responses to water stress under future climate scenarios.

中文翻译：

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表皮通透性在评估植物用水策略中的重要性。

准确理解植物对水分胁迫的反应对于量化未来气候下的生态系统碳和水循环越来越重要。从严格的气孔控制（等渗水）到明显更少的气孔控制（等渗水），植物的水分利用策略可以在一系列水分胁迫响应中得​​到表征。一种最近流行的植物用水策略分类方法是利用黎明前和中午叶片水势的回归斜率σ来反映土壤水分有效性（黎明前叶片水势）和气孔动力学（叶片水势每日下降）的耦合。 ）。这种类型的分类对于预测生态系统的干旱响应和复原力很重要。然而，它不能解释气孔对干旱枫木和白栎的相对气孔响应，在等渗谱上对它们进行不适当的排名。我们认为这种不一致可能部分归因于不同物种的表皮电导。我们使用经验和模型证据表明，具有更多可渗透表皮的植物通常被归类为等渗的。这些物种的σ值与测得的表皮通透性非常相关。此外，我们发现，随着土壤变干，具有更多可渗透角质层的物种中午叶片水势将继续降低，而对于那些具有较低渗透性角质层的物种，则不是这样。我们设计了一个诊断参数Γ，以识别表皮电导的影响可能导致物种错误分类的情况。