Wang Xia, Fan Yanli, Zhang Congcong, Zhao Yihong, Du Guangyuan, Li Min, Si Bingcheng
College of Water Resources and Architectural Engineering, Northwest A&F University, Yangling, China.
College of Science, Northwest A&F University, Yangling, China.
Front Plant Sci. 2023 Mar 16;14:1149760. doi: 10.3389/fpls.2023.1149760. eCollection 2023.
Parameterizing the process of trees from the comfort zone to mortality during progressive drought is important for, but is not well represented in, vegetation models, given the lack of appropriate indices to gauge the response of trees to droughts. The objective of this study was to determine reliable and readily available tree drought stressindices and the thresholds at which droughts activate important physiological responses.
We analyzed the changes in the transpiration (T), stomatal conductance, xylem conductance, and leaf health status due to a decrease in soil water availability (SWA), predawn xylem water potential (ψ), and midday xylem water potential (ψ) in seedlings during progressive drought.
The results showed that ψ was a better indicator of drought stress than SWA and ψ, because ψ was more closely related to the physiological response (defoliation and xylem embolization) during severe drought and could be measured more conveniently. We derived the following five stress levels from the observed responses to decreasing ψ: comfort zone (ψ > -0.9 MPa), wherein transpiration and stomatal conductance are not limited by SWA; moderate drought stress (-0.9 to -1.75 MPa), wherein transpiration and stomatal conductance are limited by drought; high drought stress (-1.75 to -2.59 MPa), wherein transpiration decreases significantly (T< 10%) and stomata closes completely; severe drought stress (-2.59 to -4.02 MPa), wherein transpiration ceases (T< 0.1%) and leaf shedding orwilting is > 50%; and extreme drought stress (< -4.02 MPa), leading to tree mortality due to xylem hydraulic failure.
To our knowledge, our scheme is the first to outline the quantitative thresholds for the downregulation of physiological processes in during drought, therefore, can be used to synthesize valuable information for process-based vegetation models.
鉴于缺乏衡量树木对干旱响应的合适指标，在植被模型中，对树木在渐进性干旱期间从舒适区到死亡过程进行参数化很重要，但目前尚未得到很好的体现。本研究的目的是确定可靠且易于获得的树木干旱胁迫指标以及干旱激活重要生理响应的阈值。
我们分析了在渐进性干旱期间，土壤水分有效性（SWA）、黎明前木质部水势（ψ）和午间木质部水势（ψ）降低导致的幼苗蒸腾作用（T）、气孔导度、木质部导度和叶片健康状况的变化。
结果表明，ψ比SWA和ψ更能作为干旱胁迫的指标，因为在严重干旱期间，ψ与生理响应（落叶和木质部栓塞）的关系更密切，并且测量更方便。根据观察到的对ψ降低的响应，我们得出了以下五个胁迫水平：舒适区（ψ > -0.9 MPa），其中蒸腾作用和气孔导度不受SWA限制；中度干旱胁迫（-0.9至-1.75 MPa），其中蒸腾作用和气孔导度受干旱限制；高度干旱胁迫（-1.75至-2.59 MPa），其中蒸腾作用显著降低（T < 10%）且气孔完全关闭；严重干旱胁迫（-2.59至-4.02 MPa），其中蒸腾作用停止（T < 0.1%）且落叶或枯萎率 > 50%；极端干旱胁迫（< -4.02 MPa），由于木质部水力故障导致树木死亡。
据我们所知，我们的方案是第一个概述干旱期间树木生理过程下调的定量阈值的方案，因此可用于为基于过程的植被模型综合有价值的信息。
