Benigno Stephen M, Dixon Kingsley W, Stevens Jason C
Botanic Gardens and Parks Authority, Science Directorate, West Perth, WA 6005, Australia.
Funct Plant Biol. 2014 Dec;41(12):1239-1248. doi: 10.1071/FP13366.
Climate change is increasing the frequency and intensity of drought, and seedling response to a recurrent pattern of drought stress is necessary to understand vegetation establishment patterns in particularly for ecological restoration and conservation projects. A controlled environment study investigated seedling physiological response of framework Mediterranean tree species to simulated successive droughts. Six-month-old seedlings were grown in 1.0m tall pots to emulate deep soil profiles and subjected to a well watered treatment and a drought treatment consisting of an initial 60 day drought (water withholding), followed by 120 days of re-watering and a subsequent 60 day drought. Soil water access, soil water content, maximum root depth and xylem water potential were assessed through successive harvests. To assess seedling response to multiple droughts, gas-exchange and chlorophyll fluorescence measurements were taken every 15 days after each drought, and multiple times throughout re-watering. No seedling mortality was observed during the initial drought, whereas 100% mortality of all species occurred within 48 days of the second drought. Seedling gas exchange and water potential decreased with decreasing water availability but was dependent on the isohydric or anisohydric behaviour of individual species. An absence of sustained photoprotection during the second drought phase heightened photodamage to foliar tissues resulting in a more rapid decrease of gs and leaf water potential. Therefore, biphasic drought proved detrimental to seedling establishment by reducing physiological resilience, highlighting the severity of future climate change predictions towards the regeneration capacity of Mediterranean ecosystems.
气候变化正在增加干旱的频率和强度，了解幼苗对反复干旱胁迫模式的反应对于理解植被建立模式至关重要，特别是对于生态恢复和保护项目。一项受控环境研究调查了地中海框架树种幼苗对模拟连续干旱的生理反应。将六个月大的幼苗种植在1.0米高的花盆中以模拟深厚的土壤剖面，并进行充分浇水处理和干旱处理，干旱处理包括最初60天的干旱（停水），随后120天的重新浇水以及随后60天的干旱。通过连续收获评估土壤水分获取、土壤含水量、最大根深度和木质部水势。为了评估幼苗对多次干旱的反应，在每次干旱后每15天进行一次气体交换和叶绿素荧光测量，并在整个重新浇水过程中进行多次测量。在初次干旱期间未观察到幼苗死亡，而在第二次干旱的48天内所有物种的死亡率达到100%。幼苗气体交换和水势随着水分可用性的降低而降低，但取决于单个物种的等水或非等水行为。在第二次干旱阶段缺乏持续的光保护会加剧对叶组织的光损伤，导致气孔导度和叶片水势更快下降。因此，双相干旱通过降低生理恢复力被证明对幼苗建立有害，突出了未来气候变化预测对地中海生态系统再生能力的严重性。
