McKiernan Adam B, Potts Brad M, Hovenden Mark J, Brodribb Timothy J, Davies Noel W, Rodemann Thomas, McAdam Scott A M, O'Reilly-Wapstra Julianne M
School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, TAS 7001, Australia.
ARC Training Centre for Forest Value, University of Tasmania, Private Bag 55, Hobart, TAS 7001, Australia.
Ann Bot. 2017 Apr 1;119(6):1043-1052. doi: 10.1093/aob/mcw266.
Drought leading to soil water deficit can have severe impacts on plants. Water deficit may lead to plant water stress and affect growth and chemical traits. Plant secondary metabolite (PSM) responses to water deficit vary between compounds and studies, with inconsistent reports of changes to PSM concentrations even within a single species. This disparity may result from experimental water deficit variation among studies, and so multiple water deficit treatments are used to fully assess PSM responses in a single species.
Juvenile Eucalyptus globulus were grown for 8 weeks at one of ten water deficit levels based on evapotranspiration from control plants (100 %). Treatments ranged from 90 % of control evapotranspiration (mild water deficit) to 0 % of control evapotranspiration (severe water deficit) in 10 % steps. Plant biomass, foliar abscisic acid (ABA) levels, Ψ leaf , leaf C/N, selected terpenes and phenolics were quantified to assess responses to each level of water deficit relative to a control.
Withholding ≥30 % water resulted in higher foliar ABA levels and withholding ≥40 % water reduced leaf water content. Ψ leaf became more negative when ≥60 % water was withheld. Plant biomass was lower when ≥80 % water was withheld, and no water for 8 weeks (0 % water) resulted in plant death. The total oil concentration was lower and C/N was higher in dead and desiccated juvenile E. globulus leaves (0 % water). Concentrations of individual phenolic and terpene compounds, along with condensed tannin and total phenolic concentrations, remained stable regardless of water deficit or plant stress level.
These juvenile E. globulus became stressed with a moderate reduction in available water, and yet the persistent concentrations of most PSMs in highly stressed or dead plants suggests no PSM re-metabolization and continued ecological roles of foliar PSMs during drought.
干旱导致土壤水分亏缺会对植物产生严重影响。水分亏缺可能导致植物水分胁迫，并影响生长和化学特性。植物次生代谢产物（PSM）对水分亏缺的反应因化合物和研究而异，即使在单一物种内，关于PSM浓度变化的报道也不一致。这种差异可能源于不同研究中实验性水分亏缺的差异，因此采用多种水分亏缺处理来全面评估单一物种中PSM的反应。
基于对照植物（100%）的蒸散量，将幼年蓝桉在十个水分亏缺水平之一上培养8周。处理范围从对照蒸散量的90%（轻度水分亏缺）到对照蒸散量的0%（重度水分亏缺），以10%的步长递减。对植物生物量、叶片脱落酸（ABA）水平、叶片水势（Ψleaf）、叶片碳氮比（C/N）、选定的萜类化合物和酚类化合物进行定量，以评估相对于对照，对每个水分亏缺水平的反应。
withholding≥30%水分导致叶片ABA水平升高， withholding≥40%水分降低叶片含水量。当 withholding≥60%水分时，Ψleaf变得更负。当 withholding≥80%水分时，植物生物量较低，8周不浇水（0%水分）导致植物死亡。死亡和干枯的幼年蓝桉叶片（0%水分）中总油浓度较低，C/N较高。无论水分亏缺或植物胁迫水平如何，单个酚类和萜类化合物的浓度，以及缩合单宁和总酚浓度均保持稳定。
这些幼年蓝桉在可用水分适度减少时就会受到胁迫，但在高度胁迫或死亡的植物中，大多数PSM的浓度持续存在，这表明在干旱期间，PSM没有重新代谢，并且叶片PSM继续发挥生态作用。
